1990 Sheila
G. Moore,
MD
George
a
Pediatric
S. Bisset
O
tnast
44.146
a
Joints,
MR
infants
and
in
Soft
neoplasms,
tissues,
Radiology
1991;
studies,
40.1214
children,
the
past
decade,
resolution
of
components
soft
magnetic
tissue
res-
and
mus-
to that of any other imand fatty and cellular
of bone
marrow
PRIMARY BONE
can be
MR portant
pose
DISORDERS MARROW
OF
The
osseous
component
of
marrow is cancellous bone, which provides architectural support for the myeloid and fat cells. Hematopoietic marmow contains approximately 40% water, 40% fat, and 20% protein, while fatty marrow contains approximately 15% water, 80% fat, and 5% protein. Red marrow has a rich sinusoidal system, while yellow marrow is supplied chief-
ly by capillaries, walled I
From
ogy,
the
S-058,
Medicine, ment
Department Stanford
of Diagnostic University
Stanford,
CA
of Radiology,
94305
Children’s
cal Center, Cincinnati stitute of Radiology,
(C.S.B.); Washington
School
St Louis
of Medicine,
partment Hospital,
School, scientific
Northwestern
(S.C.M.);
Depart-
Hospital
Medi-
Mallinckrodt University
University
(J.S.D.).
assembly.
accepted January to S.C.M. “RSNA, 1991
From
Received
29.
MR Appearance Marrow
of
In-
(M.J.S.); and DeChildren’s Memorial
of Radiology, Chicago
Radiol-
School
Address
Medical
the
1990
January
reprint
RSNA 14, 1991;
requests
veins
venules,
and
MD
pelvis, including the are the areas screened
most frequently with MR imaging for primary disorders of marrow, since these areas contain a large percentage of red
marrow
5-mm-thick
throughout images
thin-
(6).
of Normal
The MR appearance of the marrow is dependent on the relative fractions of fat and water. Cortical and trabeculam bone produce very little detectable MR signal. Signal characteristics vary with sequences and technical parameters. This discussion will focus on the use of spin-echo sequences with Ti and T2 weighting.
life.
are
Sagittal
usually
ob-
tamed in the spine, while S-mmto 1cm-thick coronal on transverse images are preferred in the pelvis and proxi-
mal femoma. images, (repetition
For Ti-weighted
a pulse time
is preferred,
for
of 300-500/20 time msec) T2-weighted
im-
or greater images,
intensity
that
spin-echo
sequence msec/echo
while
a signal
than
imaging is recognized diagnostic technique
cells.
S. Donaldson,
The spine and proximal femora,
has
as an imfor evaluating bone marrow because it provides excellent spatial resolution, anatomic detail, and the unique ability to separate hematopoietic (red) marrow from fatty (yellow) marrow (1-6). Bone marnow contains three major components: osseous matrix, myeloid tissue, and adi-
179:345-360
James
Session
ages, 2,000-2,500/70 ferred. On Ti-weighted
a
40.34
a
Focus
Imaging’
imaged.
a
40.34
VER
cle is superior aging modality,
Arthritis, 40.70 #{149}Bone marrow, 40.455, 40.64, 40.65, 40.671, 40.833, 40.92 #{149} Bone marrow, MR studies, 40.1214 #{149} Bone neoplasms, MR studies, 40.1214, 40.34 a Children, skeletal system a Joints, diseases, 40.443, 40.78 #{149} Joints, injuries, 40.41, Neoplasms,
MR
MD
onance (MR) imaging has become increasingly important in the evaluation of pediatric musculoskeletal disease. The advantages of MR imaging in the evaluation of the pediatric patient are many: (a) There is no known deletenious biologic effect; (b) there is no mequirement for intravenous contrast agents; and (c) there is no ionizing madiation. In addition, spatial and con-
terms: 40.21,
40.48,
Special
J. Siegel,
Marilyn
a
Musculoskeletal
In a review of the indications and uses for magnetic resonance (MR) imaging of the pediatric musculoskeletal system, MR evaluation of conditions unique to the pediatric musculoskeletal system were emphasized. Indications for MR imaging of the pediatric musculoskeletal system include evaluation of bone marrow, neoplastic processes, and periarticular disorders. Index 40.144,
III, MD
RSNA
med marrow
equal
of muscle
is pre-
to
or
less
in the newborn
and
greater than that of muscle but less than that of fat in children and adults. On T2-weighted images, the signal in-
tensity
is increased
and
that of subcutaneous which has a short
has a signal
may
be close
fat. Fatty relaxation
Ti
intensity
similar
to
marrow, time,
to that
of
subcutaneous fat on Ti-weighted images. The signal intensity of fatty manmow is decreased slightly on T2-weighted images, resulting in decreased contrast between yellow and cellular marrow when compared with Tiweighted images. If there is a true manrow abnormality, focal areas of low signal intensity on Ti-weighted images have greater signal intensity than that of normal marrow on T2-weighted images. Contrast between red and yellow marrow can be enhanced by low-flipangle gradient-echo imaging, short-tau inversion-recovery (STIR) imaging, and chemical shift imaging (7-10). Fat sig-
nal is decreased
in STIR
and
chemical
shift trast echo
imaging, improving tissue conand lesion conspicuity. Gradientimaging is useful in the evalua-
tion
of paramagnetic
fication,
signal
and
intensity
Abbreviation:
substances,
hemorrhage
(ii).
of the marrow
STIR
=
short
tau
calciThe
reflects
inversion
re-
covery
345
Figure 1. Normal macroscopic conversion of hematopoietic to fatty marrow. The relative amounts of macroscopic red and fatty marrow are shown for different anatomic sites (13).
0
cii 0 0
5
10
15
20
30
40
50
60
70
Age (years)
the presence of surrounding
Conversion Marrow
and
possibly trabeculam
from
Red
the amount bone (12).
to Yellow
Bone marrow, a dynamic organ, changes composition during growth and development (Fig 1). Almost all marrow space in the neonate contains red marrow. Shortly after birth, conversion from med to yellow marrow begins and progresses from the appendiculam to the axial skeleton and from diaphysis to metaphysis in individual long bones (i3,i4). In anatomic sections, theme is complete conversion of marrow in the terminal phalanges by 1 year. Macroscopic fat is observed in the midshaft of the long bones by 12-14 years and in the metaphysis by 20 years of age. The adult pattern is reached by the age of 25 years (Fig 2). Ossifying cartilaginous epiphyses and apophyses are only briefly hematopoietic, undergoing rapid conversion to yellow marmow within 3-4 months after ossification commences (15). Knowledge of the normal MR appearance and distnibution of red and yellow marrow is mequined for accurate interpretation of abnormal bone marrow conditions. Four MR patterns of bone marrow signal and heterogeneity have been descnibed in the long bones: infantile, childhood, adolescent, and adult (16) (Fig 3). The infantile pattern is found in the 1st year of life and is characterized by homogeneous low-signal-intensity marrow in the diaphysis and metaphysis. In children aged 1-10 years,
higher
signal
intensity
is ob-
served in the diaphysis, reflecting conversion of med to yellow marrow. The adolescent pattern is noted in patients aged 11-20 years. In this age group, distal metaphyseal med marrow converts to yellow marrow, producing increased signal intensity in the distal metaphysis. The metaphyseal marrow is heterogeneous due to residual islands of red marrow. The adult pattern
346
a
Radiology
is generally
reached
by
25
years
of age
and is characterized by relatively homogeneous high signal intensity in diaphyseal and metaphyseal marrow. Occasionally, low-signal-intensity foci are noted due to the presence of dense trabecular bone and the physeal scar. In general, the appearance of yellow marrow on MR images occurs at a younger age than would be expected from macroscopic anatomic data (Fig 4). Overall, marrow signal intensity comelates better with the percentage of microscopic fatty marrow than with the fraction of macroscopic fatty marrow (16). The axial skeleton is a primary source of red marrow production. In the first 2 decades of life, the vertebral marrow is rather homogeneous except for linear areas of high-signal-intensity fatty marrow paralleling the basivertebral vein (17). On the basis of anecdotal evidence, the vertebral marrow should be of higher signal intensity than the adjacent disk on Ti-weighted images in children
aged
more
than
10 years.
Mar-
mow signal intensity lower than that of the adjacent disk suggests a diffuse hematopoietic disorder. The spectrum of conversion from med to yellow marrow in the clivus and calvaria has been reported (18). Marrow in the clivus and calvania has a uniform low-to-intermediate signal intensity on Ti-weighted images obtained in most infants aged less than 1 year. Between the
ages
of
1 and
7 years,
this
poietic marrow is converted low- and high-signal-intensity By age iS years, most patients mogeneous high-signal-intensity marrow. Homogeneous lowintermediate-signal-intensity
hemato-
to patchy marrow. have hofatty or low- to marrow
in the skull or in the region of the clivus should be considered abnormal in any child aged more than 7 years. The signal intensity of occipital, panetal, and frontal calvanial marrow in males tends to be somewhat greater than that in females during the 2nd decade only. Two normal patients in this
Figure 2. Normal distribution of adult marrow. Macroscopic red marrow resides in the vertebral bodies, flat bones, and proximal metaphyses of the femora and humeri (shaded areas). The remainder of the skeleton (white areas) contains primarily yellow marrow (6).
study
had
low-
intensity the
to
marrow
2nd
decade
peamance
of
patients
of
lie
limits.
aged
Four
less
region
pelvic
than
mediate of
In
10 years, tensity acetabulum.
Mild
heterogeneity anatomic
20
years,
ity
on
MR
tenor
ilium.
increased signal the years
of
increased
the
anterior
intensity pelvis
in
In
persons
at aged
these 11-
hetemogene-
is not
uncommon,
the
acetabulum
Marrow
signal with
seen
and
marrow
sites.
children
in-
ilium
observed
compared
1 and signal
moderate
marrow
inter-
1st year
between
be
in
to
in the
to
images
in ho-
low
may marked
particularly
of
aged in
of
have
skull.
intensity
is seen
outside
is relatively
children marrow
normal
marrow
the
marrow
signal
life.
two
of
med
ap-
in
1 year
marrow
mogeneous
into MR
percent
fatty
frontal The
the
marrow
high-signal-intensity the
calvamia so
occasionally
accepted
children
the
life,
calvamial
may
these
intermediate-signalin
in
and the
all
aged
an-
intensity
is
marrow
regions less
of than
10
(19).
May
1991
a. 3.
Bone
Marrow
d.
C.
b.
Figure
Normal MR patterns of appendicular marrow. (a) Infantile pattern: Coronal Ti-weighted image of the pelvis and left femur of a 1-year-old boy shows low signal intensity in the diaphysis and metaphysis, reflecting the predominance of hematopoietic marrow. The ossified femora! head is of higher signal intensity because it contains yellow marrow. (b) Childhood pattern: Coronal Ti-weighted image through the distal femur of a 6-year-old girl shows high signal intensity in the diaphysis as well as the epiphysis, reflecting the presence of yellow marrow. The metaphysis has a signal intensity greater than that of muscle but less than that of fat, reflecting a greater red marrow fraction. (c) Adolescent pattern: Coronal Ti-weighted image of the distal femur and proximal tibia of a 16-year-old boy demonstrates high signal intensity in the diaphysis, metaphysis, and epiphysis consistent with distal metaphyseal conversion of red to yellow marrow. The distal metaphyseal marrow is patchy, reflecting residual islands of hematopoietic marrow. (d) Adult pattern: Corona! Ti-weighted image of the pelvis and femora in a 26-year-old woman shows relatively homogeneous high-signal-intensity yellow marrow in the epiphyses and diaphyses. The linear foci of low signal intensity in the metaepiphyseal region of the proximal femora represent the closed physes. The signal intensity of the femora is greater than that of the ilia, reflecting the greater percentage of red marrow in the flat bones.
is not possible on the basis of the MR appearance alone but requires commelation with the clinical context. Iron overload may occur in chronic disorders of erythropoiesis, due to mecurrent hemolysis and frequent blood transfusions. Iron deposition occurs primarily in the liver, spleen, and bone marrow. In these cases, marrow signal intensity decreases on Ti- and T2weighted images (20). Marrow changes may be diffuse or focal (Fig 7).
Disorders
Hematologic disease that affects bone marrow can be divided into four groups: myeloid hyperplasia, marrow replacement, myeloid depletion, and myelofibmosis.
Myeloid
Hyperplasia
Increasing sis
may
demand
stimulate
marrow
for
for
hematopoie-
recruitment
red
of
marrow
This
phenomenon,
sion,
results
from
mias
(sickle
cell
yellow
production.
termed
meconvem-
severe
chronic
anemia,
Marrow Infiltration
thalassemia),
marrow replacement disorders, or cyanotic heart disease. The pattern of meconversion is opposite that of physiologic red-to-yellow marrow conversion (Fig 5). In severe anemias, the epiphyseal marrow, which is normally fatty, may
convert
On nal
on
tissue
images,
than
the
amounts and
subcutaneous
neoplastic
Volume
of cellularity may
be
a
less
greater
than
The is not specific and is of marrow replacement fat
(Fig
processes.
179
and
slightly
or slightly
to,
MR appearance identical to that by
sig-
similar
that of muscle. On T2images, the signal intensity to a variable extent, depend-
equal of
marrow and
Number
6).
Differentiation
2
to
of
both
red
and
yellow
cantly
different
among
marrow by malignant cells will result in intermediate to low signal intensity on Ti-weighted images and increased
groups relaxation nosing
signal
images
mission
diffuse
can help differentiate ease from hypemplastic
intensity
(3,21-23).
marrow.
is decreased
water,
than, that
red
Ti-weighted
intensity
or less weighted increases ing
to
Replacement
ane-
temization and assessment of extent of an abnormality suspected on the basis of marrow aspiration or other imaging studies, evaluation of focal areas of bone pain, and assessment of response to treatment. Ti relaxation times of marrow in leukemia have been reported (22) and may be useful in determining the stage of disease. These marrow relaxation times are significantly longer in children with active disease than in children with leukemia in remission or in agematched controls (Fig 9). T2 relaxation times of bone mammow are not signifi-
The
on
T2-weighted
changes
are
often
in leukemic infiltration, but focal involvement may also be seen, especially in acute myelogeneous leukemia (21). Metastases and lymphoma are usually focal, well-defined lesions (Fig 8), although the margins can be poorly defined if there is marrow edema associated with the lesions (24). Occasionally, there is replacement of the entire marrow by metastases. Although MR imaging is sensitive for
diagnosing
infiltrative
not a practical screening indications for its use
disease,
tool. include
Primary chamac-
it is
Myeloid
(22).
The data times may acute disease, in
patients
these
suggest be useful relapse, with
various
that Ti in diagand me-
leukemia
and
neoplastic disred marrow.
Depletion
Myeloid depletion is characterized by a hypocellular or acellulam marrow with primarily adipose cells and areas of fibrosis. Causes of myeloid depletion include drugs, toxins, viral infections, radiation therapy, and chemotherapy. On Ti- and T2-weighted images, untreated aplastic marrow demonstrates an increased signal intensity, similar to that of subcutaneous fat, reflecting the
Radiology
a
347
Carthage
24
20
12-14
7
Birth
J
Red
Birth
Yellow
Cartilage
Figure 4. row change
MR
appearance
with
macroscopic
age.
sections,
percentage
versus
The
signal
which
of microscopic
reflects fatty
anatomic
intensity
marrow
distribution.
of the marrow
the sensitivity marrow than
Yellow
on (Fig
Ti-
and
T2-weighted
images
ii).
In Gaucher disease, the marrow becomes infiltrated and replaced by glucocerebroside-laden cells as well as fibmosis. Marrow involvement usually follows the distribution of red marrow, occurs first in the spine and flat bones, and then progresses from proximal to distal in long bones, with sparing of the epiphyses. The abnormal tissue produces a low signal intensity on Tiand T2-weighted images (28-30). Acute and chronic marrow infamction, due to marrow packing, are complications of Gauchem disease. Acute bone infarcts are seen as focal areas of decreased signal intensity on Tiweighted images and increased signal intensity on T2-weighted images. Oldem, fibrotic infarcts appear as low-signal-intensity
weighted
a
appearance
and
is greater
to detection fatty marrow.
than
(b)
macroscopic
would
of fatty marrow. (Adapted from
be expected The MR reference
appearance of red and yellow marfrom examination of anatomic appearance correlates better with 14.)
75 0 cii 0 0
50
cc 25
Myelofibrosis is the result of replacement of normal marrow by fibrotic tissue. Although uncommon in childhood, it is most often the sequela of chemotherapy or radiation therapy for leukemia, lymphoma, or metastases on of Gaucher disease. Rarely, it is a primany process characterized by splenomegaly and diffuse stromal marrow meaction. Replacement of the marrow by fibrosis results in decreased signal in-
348
Red
100
Myelofibrosis
tensity
(a) MR
on MR images
of MR imaging with macroscopic
high fatty content and lack of cellular marrow (23,25,26). Myeloid depletion is particularly noticeable in the spine following radiation therapy, with increased signal intensity on Ti-weighted images (Fig iO). With successful treatment, areas of low signal intensity appear in the yellow marrow, representing islands of active red cells.
(27)
j
24
20
b.
a.
the
12-14
7
foci
images.
Radiology
on
both
Ti-
and
T2-
0 Time Figure 5. undergoes in a proximal
Response Therapy
of the
Reconversion
of yellow to red marrow. The first, followed by the appendicular sequence (13).
reconversion to distal
Marrow
ages, subtle
to
Radiation therapy, marrow transplantation,
chemotherapy, and multiple
transfusions
used
are
each
in
the
on
Ti-weighted
and
STIR
marrow marrow
while on T2-weighted images, patterns of inhomogeneity and
mottling
are
more
difficult
to
appreci-
ate.
treat-
ment of pediatric disease. Each of these treatment modalities may affect the appearance of pediatric bone marrow. The MR appearance of the lumbar spine marrow in the first few weeks following radiation therapy has been reported (31). Theme are no appreciable differences in marrow signal intensity on spin-echo Ti- or T2-weighted images between pmetherapy examinations and those performed at 10-14 days; however, on STIR images, increased signal intensity can be seen at 10 days, corresponding to the marrow edema that predominates at this stage. Within 3 weeks after radiation therapy, there is either an increase in central fat or a mottled appearance to the vertebral marrow
axial
im-
Two “late” marrow patterns on Ti-weighted images: either geneous, increased-signal-intensity vertebral marrow-reflecting ment of red marrow by yellow (32,33)-or
a second
pattern
are seen homoreplacemarrow of
central
increased-signal-intensity fatty and peripheral intermediate-signal-intensity
med
marrow
(31).
marrow
Occasionally,
the marrow may respond primarily with fibrosis. Further studies in children are needed to define both the appeamance of vertebral marrow months to years after radiation therapy and the early appearance of the appendiculam skeleton following radiation therapy. MR changes following chemotherapy
have
been
long bones spond with
reported
(34,35). The hyperplasia
primarily
in
the
marrow may meand fatty me-
May
1991
Figure
7.
Ti-weighted sagitin an adolescent with sickle cell anemia shows diffuse decreased marrow signal intensity. Signal intensity was also diminished on the T2-weighted im-
tal image
b.
a.
Figure 6. Reconversion in sickle cell anemia. (a) Ti-weighted coronal image of the distal extremities shows low-signal-intensity red marrow in the tibial diaphyses, metaphyses, and epiphyses. Patchy foci of high signal intensity in the metaepiphyseal region correspond to residual islands of fatty marrow. (b) On the T2-weighted coronal image, focal areas of high signal intensity in the marrow represent areas of acute medullary infarction. Acute infarct can be difficult to distinguish from osteomyelitis on the basis of MR images alone.
Iron
overload.
of the spine
age.
E
ALL
ALL
Relapsa
b.
a.
Figure 8. Hodgkin lymphoma in an 18-year-old man. (a) Ti-weighted coronal image obtamed through the pelvis and femora shows low-signal-intensity tumor, replacing the marrow in the proximal metadiaphysis of the right femur as well as in the right iliac crest. The left femur and ilium are normal for comparison. (b) On the T2-weighted image, the signal intensity in the femoral and iliac marrow increases slightly more than normal. Marrow infiltration is usually best depicted by shorter rather than longer pulse sequences.
placement, resulting creased-signal-intensity images.
After
the
in diffuse inmammow on transition
from
gions
MR
initial
congestive edema to fibrosis, the marmow may appear as low signal intensity on both Ti- and T2-weighted MR images and may be patchy or homogeneous.
red
Apparent marrow
reconversion following
chemothemapy gmessively intensity
Volume
may
of yellow to treatment with be
decreasing appearing
179
a
seen, marrow
first
Number
in
2
with
pro-
signal marrow
not
expected
be
flat
expected
hematopoiesis
bones) to regions to contain
(eg,
and occasionalthat would med
marrow.
In some patients, areas of osteonecrosis may develop, which is attributed to the use of steroids or cytotoxic drugs (35). Prospective studies describing the appeanance of pediatric lesions of the bone following the administration of either radiation or chemotherapy have not
me-
of
metaphysis, ly progressing
been
Marrow
performed.
transplantation
is an increas-
ALL RemIssion
Normal
Figure 9. Ti relaxation times in children with leukemia. Histogram of the Ti relaxation times of the vertebral marrow in patients with newly diagnosed acute lymphocytic leukemia (ALL), leukemia in relapse (ALL Relapse), leukemia in remission (ALL Remission), and normal age-matched controls. Marrow Ti relaxation times are markedly prolonged in children with active leukemia compared with children with inactive disease and age-matched controls. Standard deviations for the various groups are noted. (Reprinted, with permission, from reference 22.)
ingly
used
form
of
therapy
for
pediat-
nc disease. Following pretmansplantation ablation therapy, marrow cells are infused intravenously and are typically engrafted oven the next 3-4 weeks. The appearance of the vertebral marrow following transplantation in i2 children has been described and consists of a peripheral zone of intermediate signal intensity surrounding a central zone of high signal intensity on Tiweighted images (36). This alternating zone of intermediate and high signal
Radiology
a
349
a. Figure
b. 11.
pharyngeal
Marrow
fibrosis
carcinoma
in a 16-year-old
metastatic
to
the
girl, left
who
ilium.
received
(a)
radiation
Transverse
therapy
for
Tl-weighted
naso-
image
demon-
strates low signal intensity in the marrow of the left ilium (arrow) and the left half of the sacrum (arrowhead). (b) On the T2-weighted image, low-signal-intensity marrow persists in the left ilium (arrow), but increased-signal-intensity marrow is noted in the left half of the sacnum (arrowhead) as well as in the soft tissues adjacent to the ilium. Biopsy revealed fibrotic marrow in the left ilium and recurrent tumor in the sacrum and soft tissues.
Figure 10. Myeloid depletion in a 16-yearold boy who underwent radiation therapy
10 months previously for lymphoma metastatic to the lumbar spine. Sagittal Tiweighted image shows high-signal-intensity marrow in the lower lumbar spine, consistent with fatty replacement. The vertebral marrow outside the radiation port has a more normal intermediate-low signal intensity.
intensity is termed the “band pattern.” This band pattern is detected in almost all children within 90 days following transplantation. Pathologic comrelation of the band pattern shows a peripheral
zone
topoietic
cells
nipheral
of
nepopulating
corresponding
intermediate
hemato
signal
the
pe-
intensity
on MR images. The central zone of increased signal intensity corresponds to fatty marrow surrounding the basivertebmal vein (36). Following transplantation, loss of the band pattern and appearance of a diffuse low-signal-intensity homogeneous marrow may herald a relapse of disease in those children with hematologic malignancies. Further long-term studies are needed to determine whether loss of the band pattern can also represent a normal marrow pattern in the months to years following transplantation.
Marrow
Edema
Marrow eralized
edema response
is a nonspecific, of
the
marrow
gento
stress or injury. While the stimulus of and controlling factors in the initiation of edema are uncertain, it is known that the amount of extracellulam water
350
a
Radiology
Figure
12. Coronal Ti-weighted image of the distal femur in an 8-year-old girl with an osteoid osteoma of the distal right femur. Thickening of the cortex (arrows), which remains of low signal intensity, is seen surrounding the lesion. The low-signal-intensity marrow edema is extensive, with a sharp demarcation between normal and edematous marrow (arrowheads). The presence of marrow edema with thickening of the cortex and no evidence of soft-tissue edema or mass should suggest the diagnosis of osteoid osteoma (3).
Figure
13. left
girl.
The
marrow
farct
is the
row,
with
rim,
which
signal
fined
Ti-weighted
sharp margin between normal marrow (Fig defined and feathery. diagnosis of pediatric
with
a fairly
normal and ab12), or it can be illThe differential marrow edema
same
as
acute
trauma,
reflex
osteoid
osteoma,
“Transient”
been pain
in an
that
of
of
inmar-
bone.
from
edema and
94.)
due
to
ischemia,
chronic and
marin-
infection,
sympathetic
dystrophy, tumor. abnormalities
in children these in
(Re-
reference
osteoporosis,
In
the
low-signal-intensity
marrow
intensity
il-year-old
sclerotic
reported (37).
older the
surrounding
permission,
or
an of
intensity
“transient”
famction,
hip
(arrow) signal
represents
stress
have
and infarct
a serpiginous,
includes row
tibia
with
increases as a result of hypervasculamity and hyperperfusion. The increase in extmacellular water is most likely modulated by the severity of the hypervasculanity and hypemperfusion. The MR image will reflect this increase. Marrow edema is seen as low to intermediate signal intensity on Tiweighted images, which increases on T2-weighted, fat saturation, and STIR images. Marrow edema can be well degeographic,
lymphoma medullary
proximal
printed.
and
Known
therapy-induced
the
images
with
children,
low
femoral
head
eventually
solves,
reverting
to
marrow
signal
intensity.
coincides ment in
with documented the child’s clinical
on
me-
a normal
pattern This
of
reversion
improvecondition.
May
1991
particularly
sensitive
to
marrow
or
soft-
tissue abnormalities. Theme has been some suggestion that the finding of fluid surrounding the bone at ultrasound examination is specific for osteomyelitis; however, recent reports have shown that this finding is not specific for osteomyelitis. While madionuclide bone scanning may be sensitive for detection of osteomyelitis, it is probably
not
as sensitive
as
MR
aging. In one recent study, MR was positive in six of six patients, a.
b.
Figure
14. acute
with ischium
(a) Ti-weighted osteomyelitis
(arrow),
with
intercalation
fat
saturation
image
transverse is seen
throughout
head)
and
into
tis
fat
saturation
on
transverse of the right
the
the
right
soft
tissues.
image ischium. of
infection
obtained ischial
The
just
scintigmaphy
through the femoral Low signal intensity through
the
inferior
marrow,
extending
increased
signal
to the
head in a 2-year-old is seen within the
cortical
of a. High
through
the
intensity
(b) T2-weighted
bone.
plane
signal
cortical
is typical
boy right
intensity
bone
for
(arrow-
acute
osteomyeli-
images.
was
teomyelitis
is marrow signal
ed images specific marrow changes. Children with sickle cell anemia, Gaucher disease, or hematopoietic malignancies and those undergoing steroid therapy can all be first seen with medullary infarction. Differentiation between early acute medullary ischemia and transient marrow edema based on the MR appearance alone is not
Figure
15.
(200/i5,
Coronal
30#{176} flip
gradient-echo angle)
image
obtained
through
the distal femur in a boy with Ewing ma. The low-signal-intensity Codman gle (arrow) and the calcified Sharpey (arrowheads) extending through the sue mass can clearly be seen.
possible,
While sarcotrianfibers soft-tis-
sient
bone
some
unknown
are marrow
and
has
acute
Calv#{233}-Perthes diogmaphs mild
symptoms
disease)
by
would On
dence,
the
normal osteoporosis.
pain specific
basis MR
of
(low
tensity
Volume
a
that or
anecdotal of on images),
representing
seen The
gain
on
a signal of
the
diagnosis
sity
that
myelitis.
While
diatnic
osteomyelitis
me-
is equal
is increasingly
to
used
evaluation most
of
cases
are
metaphyseal
in
osteo-
in
interface mal
marrow
Marrow become duration peniosteal
Theme
or
the
articular
epiphysis.
tive
for
tion
and
capsule of
the
earlier
reports
ing
was
of
evaluating
While
early
detection
peniosteal
CT
may of bone
reaction,
be
cortical
for
thickening,
Cortical
sensi-
seen
as
it is not
fat
be
and
pemios-
bone
and
evaluated or
edema,
bone with
will
usu-
transverse
associated
lesions width
is often of
spin-echo,
images.
pen-
with
be
thickening
on
with con-
lesions,
should
increased
saturation
method
evaluated
evaluated
nonaggressive
imag-
good bone
Cortical
with
bone
MR
While
infiltration
and
cortical
that
(42). musculoskeletal bone
best
severity
experience lesions
cortical can
MR imaging In pediatric the
the
a particularly
both
the ab-
infection.
cortical
either
images;
pemiosteal
with the
be
MR
or
teal reaction, further pediatric musculoskeletal that
destruc-
on
suggested
not
images.
in pacan
abnormal
of
cel-
pemiosteum
increases
reaction
encloses
metaphysis
associated
a be
abscess.
and
duration
may
by the time there will abnommali-
either
of cortical
be
the
defined.
osteomyelitis
firmed
in
abnor-
inflammation
be
cortex with
ally
ankle
the
and
poorly
soft-tissue
as
and
infection,
Usually, imaging, of soft-tissue
may
or
destruction.
shoulder,
of
normal
soft-tissue
be appreciated. child undergoes MR evidence
and
14).
is often
and
hip,
but
signal increases and margins better defined with increasing of infection. Surrounding
spread across the growth plate and involve the epiphysis, especially in infants and young children. The epiphysis can also be involved in joints such the
low images
abnormality,
course
between
osteal
can
of infection,
(Fig
the
pe-
infection
sig-
images.
Ti-weighted
MR
is increased
to the
of acute
confined
only
normality
usually
to increased
hours on
de-
Ti-weight-
T2-weighted
few
the
Early
The
unaffected
and
a portion
with-
be
tients
(Fig
will
intensity
marrow. MR imaging
both
in-
may
ty.
sclerotic
madiographs
marrow
surrounding
which
Ti-
plain
central
transient effu-
difficult
six
as the infection progresses and the time between the onset of infection and performance of an MR examination increases, increasing signal intensity will be seen on the T2-weighted images (41). On T2-weighted fat saturation and STIR images, the marrow signal inten-
likelihood
rim
hip signal
2
tu-
evi-
increased
Number
accom-
trauma,
intensity
T2-weighted
179
not
of a simple
images, on
The
be
intensity
the
a serpiginous
metaphysis,
show
symptoms
appearance
signal
of ma-
may
first
normal
the
cases
or
are
infection,
consists
weighted
In
of
acute
(38)
edema,
be
the
synovitis
(39).
marrow
other
associ-
(Legg-
degree
suggest
mor.
to
been
should of
panied
also
necrosis
pediatric
some
secondary
infarcts
of
with
on
normal on
In the
low-signal-in-
with
13).
tran-
osteoporosis
avasculam
transient
to
are
and
signal
ities,
that
aggressive
early
sion
edema
edema
with
due
stimulus.
Transient
ated
likely
entities
five
edema,
intensity
intensity
lulitis
bone changes
both
nal
to diagnose definitely, older infamcts have a much more typical appearance. These are seen as geographic abnormaltensity
These
since
seen on MR images as marrow edema. While early medullary infarction will be seen as an ill-defined region of low signal intensity on Ti-weighted images and increased signal intensity on T2weighted images, medullary infanctions usually become well defined and geographic in appearance fairly quickly (Fig 6). Depending on the cause, marrow infarction can be peniarticulam or present anywhere within the medullamy cavity.
in
patients (40). In addition, scintigraphy does not accurately define the full extent of infection, and it is sometimes difficult to separate soft tissue from bone infection (41). The earliest MR finding of acute oscreased
out
positive
im-
imaging while
the
black
STIR, This
can
Radiology
and be
seen
a
351
with
cortical
sions
buttressing
that
such
result
in
as osteoid
and
cortical
with
le-
thickening,
osteoma
(Fig
12).
Edema
of the cortical bone or involvement of the cortical bone by a pathologic process such as infection or intercalation of tumor through haversian canals will be seen as intermediate signal intensity within the normally black cortical bone. The MR appearance of peniosteal meaction has been described (42,43). On spin-echo MR images, peniosteal reaction can be appreciated as either intermediate signal intensity on Ti-weighted images that increases on T2-weighted images on low signal intensity on both Ti- and T2-weighted images (Fig 15). Peniosteal reaction that is low signal
intensity
on
both
Ti-
and
T2-
weighted images represents lamellam pemiosteal reaction. Complex peniosteal reaction, such as spiculated peniosteal reaction or lesions with new bone formation (such as osteogenic sarcoma), may not be appmeciated as calcified on MR images, since complex pemiosteal reactions comprise structurally disorganized bone embedded in a protein and/or tumor matrix.
Figure
16. Transverse proton-density image obtained through the distal a child with chronic osteomyelitis. cortical thickening is present, and course and depth of the sinus tract the cortex can be identified. Increased intensity
and
in
the
marrow
surrounding
musculature
represents
persistent
tion
will
reveal
abscess,
The
can
nal.
drainage. In healed bone marrow may
Pitfalls
in
the
evaluation
bone,
of
mined the
pemioste-
al reaction on MR images include partial volume averaging in regions of rapidly tapering bone and of cartilaginous epiphyses and muscle attachments, the presence of a soft-tissue mass adjacent to the bone, and postemion femonal hypemostosis. The MR examination should never be interpreted
with size
This
the
of
the
MR
as
ing
tion
of
image,
minimizing
necessary
low
signal
to
intensity
The
for
intensity
soft
images. intensity
In may
these
entities
sions
such
signal
both
Ti-
Areas as low
intensity
on
and
T2-
of active infecto intermediate
Ti-weighted
im-
ages, with increased signal intensity on T2-weighted images (41,44). The course and depth of sinus tracts can be appreciated within both soft tissues and contical
bone
(Fig
elitis,
the
often
well
ty,
theme
osteomy-
infection and
tissues
are
marrow
bone,
Soft
in
are
cavithe
soft
almost
in-
imaging
is useful
of
pediatric
osteomyelitis,
the
planning evaluating
sion
to
known
a
a role
for
MR
need
for
surgical
the surgical the response
therapy.
In
osteomyelitis,
Radiology
a case
in
fatty
The the
appropriate
presence
will
will
in
approach, of the of suspected
examina-
le-
child
marrow,
the
images
with
predom-
be
confined
the not
be and
to
cortical
the
bone,
accompanied
and by
joint
effusion
fractures
can
do
may
not
or
soft-tissue be
on The osteoid
as
and
involve
The
nidus
and
have
signal
bone images.
on
both When
Tistress
and
T2fractures
signal that
can of
of
the
shaft
(Fig
appearances: Ti-
decreased
low and
T2-
signal
and
in-
T2-weighted
signal images on
exten-
identified
increased
intensity
accom-
be
be
both
Ti-
the
which T2-weighted
often
on
Ti-weighted
intensity
and
increased
T2-weighted
im-
ages. Cortical
“edema”
has
osteoid
osteoma
(46).
in ence
of
sive
cortical of
or
no
should osteoma,
can
a
child
ed
the be
be
extensive.
presents of
is usually after cortical more
osteoid the plain
the
cortical
accompanied
by
edema this
clinical than
imaging
and
the
may
or
reason, computMR
imag-
modality
radiography,
if
symptoms
osteoma,
rather
abnormality easily
suggest
For
with
tomography,
ing,
be
pres-
exten-
thickening, marrow
not
the
and
edema
cortical
reported
While
osteoid
osteoma
little
been
thickening
marrow
diagnosis
choice
weighted
and
much can
both
or
at
in by
edema
images,
signal
osteoma
as decreased
a variety
on
low-signal-intensity
to cortical
frac-
setting,
Ti-
intensity
suggestive
perpendicular
stress
thickening,
osteoma
i2).
nonspecific “marrow edema.” They can be accompanied by extensive marrow edema, or they can be seen as a focal line
image of
osteoid
marrow
sive
may seen
pres-
be suggested,
both
accompanying
(45). also
of
appreciated
images,
marrow,
the
T2-weighted
clinical
images.
osteoid
are
and
diagnosis
cortical
panies
tures
involve
How-
low-signal-in-
should of
tensity
trabecular
le-
tumor.
bone
diagnosis
imaging
The
T2-weighted
aggressive or
the
the
MR
on
Stress drain-
on
In an older
on
distinguish
tume.
micmofmactume is best seen on Tiweighted images. In an infant or youngem child with predominantly hematopoietic marrow, a trabecular microfractune may not be appreciated on the Tiweighted images. These lesions will be seen as increased signal intensity on T2weighted images. Tmabeculam microfrac-
injury
the
imaging
MR
intensity
i7).
inantly
may
MR is also
assessing
352
the
in the
cortical
diagnosis
or
chronic
abnormal.
While
age, and
of
defined
(4i).
variably
In
margins
within
tissues
i6).
(Fig
more
cortical
line
marrow to
infection
suggest
weighted
on
images. be seen
ma-
plain
permission,
extensive
from as
intact
signal
intensity
weighted tion will
plain
mi-
a negative
difficult
of a perpendicular
signal
of a recent
by be
ence
diogmaphic examination. Chronic osteomyelitis can be chamacterized by areas of overgrowth of bone and sclerosis, which will be seen as low
benefit
trabecular
with with
ever,
by deposireturn
in
3.)
it can
heal tissues
mar-
a ski-
image.
extensive
a patient
surrounded
edema,
can
hu-
following
T2-weighted
(Reprinted,
tensity on
the an
in reference
intensity
the
on
represented
normal.
occasionally fat.
for
be deter-
boy
A region of low signal intensity the marrow on the Tiimage (arrow), which increased
weighted
are
for
osteomyelitis, the heal with scarring.
return
may
of
Ti-weighted proximal
within
to normal. Medullary trauma will also be accompanied by marrow edema. In children, tmabecular fractures or bone contusion will result in an ill-defined area of low to intermediate signal intensity on Ti-weighted images and increased
without
a 17-year-old
injury.
is seen
This
need
approach
also
and T2-weighted marrow signal
completely
row
the
incision
appears
both Tichildren,
foci
indicating
drainage
lamellam
of
signal
infection.
well-defined
marrow
drainage.
in
merus
from
surgical
protons
17. Oblique coronal obtained through the
radiograph.
surgical
the
Figure image
crofracture
which do not resonate during clinical proton MR imaging, these protons are free to resonate and will result in sig-
Unlike
MR femur in Marked the through signal
of
since and
nidus
may
appreciated.
May
1991
PEDIATRIC MUSCULOSKELETAL TUMORS Bone
Figure 19. Transverse proton-density fat saturation image obtained through the left side of the chest of a 7-year-old boy with a soft-tissue abscess. A focal region of highsignal-intensity infection is seen (arrow), and edema extends anteriorly around the chest wall.
seen on “transient,” Figure
18. Coronal Ti-weighted image obtamed through the distal femur in a boy with primary bone lymphoma. Note the sharp delineation between intramedullary tumor and normal fatty marrow (arrow). Also demonstrated is transphyseal extension
of tumor
into
the distal
heads). The distal with intercalation
epiphysis
(arrow-
cortical bone of tumor.
is thinned,
Finally, diffuse medullamy tumors, such as Ewing sarcoma or lymphoma, can be difficult to distinguish from fuse marrow edema. Intramedullary mom
is usually
normal
sharply
marrow,
companying
demarcated
and
there
endosteal
thinning,
and
diftufrom
is often
cortical
involvement
ac-
erosion, of cortical
the
MR examination may be secondary to mild osteopo-
rosis,
infarction,
ulan
micmofnactume
trauma or
such bone
as
trabec-
contusion,
or reflex sympathetic dystrophy. The presence or absence of soft-tissue
edema
is similarly
important
margins,
in
the
differential diagnosis of marrow edema. Recent studies have suggested that more aggressive processes are accompanied by marrow edema, while slowgrowing tumors and less aggressive processes are accompanied by less softtissue edema (47). If there is extensive soft-tissue edema surrounding an area of marrow edema, acute trauma and acute inflammation should be considemed. If theme is a moderate to small amount of edema surrounding the marrow abnormality, slow-growing tumor, chronic infection, and subacute trauma
bone (Fig 18). A soft-tissue mass should suggest either tumor or infection. When a marrow abnormality is identified on a pediatric MR examination, the clinical history, physical examination, and plain radiogmaphs are pivotal in the differential diagnosis. If the marrow edema is pemiarticular, one can
should
consider
Hemorrhage caused by acute trauma can also masquerade as a soft-tissue mass. MR imaging is the examination of choice in the evaluation of soft-tissue infection. On Ti-weighted images, softtissue infection will be seen as low to intermediate signal intensity with increased signal intensity on T2-weighted images (Fig i9). The adjacent marrow will be normal unless there has been tmanscortical spread. In cases of
the
crofracture infarct.
diagnosis
and If the
of
trabeculam
peniarticulam marrow
mi-
medullary
edema
is diffuse
and well defined, one can consider infection, osteoid osteoma, and tumor. Finally, the presence of cortical thickening,
soft-tissue
edema,
and
a soft-tissue
mass can be helpful in the differential diagnosis of marrow edema. If the cortex is eroded or theme is increased tex
signal
intensity
indicating
gressive
within
intercalation process
the of
through
the
an
corag-
cortical
be
rounding
row
considered.
If theme
soft-tissue
edema
represent
edema,
identified
edema,
tumor
and
cellulitis,
infection
the
are
cal
diagnostic
Volume
179
a
Number
the
marrow
2
edema
intensity. signal
that
signal
likely
to
bone
con-
signal images
intensity
conform
on
to the of
fasciitis.
likely.
intensity
while abscess can be displace normal tisareas of fluid signal
Intermediate
on Ti-weighted
most
abnormal
can be ill defined, well defined, will sues, and can have
is normal,
sun-
mar-
tusion, stress fracture, or medullany infanction. Finally, if there is a soft-tissue mass associated with the abnormality,
bone, tumor, infection, and aggressive osteoporosis are more likely. If the cortical bone is thickened but maintains a signal void on both Ti- and T2-weighted images, diagnosis of osteoid osteoma, stress fracture, and chronic infection should be considered. If the cortibone
is more
“transient”
is no the
and
intensity increased
T2-weighted
fascial
images
planes
Tumors
The evaluation and treatment of musculoskeletal tumors in the pediatric population has changed dramatically in recent years, partially as a result of significant developments in imaging studies. The advent of MR imaging and the refinement of limb-salvage surgical techniques have contributed significantly to improved survival (48-50). The role of imaging in bone tumors includes lesion detection and characterization, staging, treatment planning, and postthenapy follow-up. Plain radiography remains a reliable method for predicting the histopathologic nature of a specific skeletal lesion. Detection and characterization of a skeletal lesion rely on localization of a lesion, assessment of lesion extent and
are
evaluation
of
cortical
destruc-
tion and pemiosteal reaction, presence of adjacent soft-tissue mass, and identification of lesion matrix. These findings can usually be accurately assessed with plain radiography, and a working differential diagnosis can be generated. Currently, the role of MR imaging in diagnosing a specific lesion is somewhat limited. The technique, although sensitive, is nonspecific. Early attempts to predict lesion histologic findings at MR imaging have been disappointing (Si,S2). Although this shortcoming may be partially related to the nonspecificity of proton imaging, an even greater drawback may be the relative lack of experience with MR imaging (Fig i5). As experience and scientific research in the MR appearance of bone lesions
accumulate,
the
predictive
val-
ue of this modality may improve. To determine the need for further imaging studies in the case of a pediatnc skeletal lesion, the plain radiograph is first evaluated. A “do-no-evil” lesion (eg, fibrous cortical defect) requires no further evaluation. Some lesions (eg, osteochondromas)
may
require
follow-
up radiography and possibly MR evaluation, particularly with clinical changes in size or symptoms. On the MR examination, malignant degeneration of an osteochondroma to a chondrosarcoma is characterized by disruption of the cartilaginous
cap
and
presence
soft-tissue mass that is contiguous the osteochondroma. This mass as intermediate signal intensity weighted images and increased intensity on T2-weighted images. There has been some suggestion the degree of thickening of the laginous cap can be suggestive lignant nous
cap
change.
In
more
than
adults,
of
a
with is seen on Tisignal that cartiof ma-
a cantilagi-
3 cm
thick
RadioIoQv.a
is con-
Figure
20.
obtained
Transverse through
with osteosarcoma. tercalated through tibial
cortex
heads). This disease.
proximal
image tibia
Although the anterior
(arrow), by the indicates
be contained
Ti-weighted
the
in a girl
tumor has inaspect of the
the tumor appears periosteum (arrowintracompartmental
to
a.
b.
Figure 21. (a) Transverse T2-weighted with primary bone lymphoma. There sive extracompartmental quence 4 months
planes
and
after
disease. the initial
no evidence
image
obtained
are obliteration
(b) Follow-up image image demonstrates
of significant
residual
through
the
distal
of intermuscular
thigh
in a boy
fat planes
obtained with reestablishment
an
and
exten-
identical pulse of intermuscular
sefat
tumor.
sidemed suspicious for malignant degeneration (53). However, thick camtilaginous caps are generally seen in children, and there have been, to our knowledge, no prospective studies measuring the normal thickness of the cartilaginous cap in pediatric osteochondroma. Therefore, it is less likely that this criterion will be useful in the evaluation of possible malignant degeneration in pediatric osteochondroma. Other lesions (eg, large unicameral or aneurysmal bone cysts) require cunettement with possible bone grafting to prevent pathologic fractures. Finally, when biopsy and possible surgical memoval of a lesion are deemed necessany,
MR
imaging
plays
a crucial
role
in
staging and treatment planning. The goals of such planning relate to preserving limb function and minimizing the chances of local recurrence. Both the intmaosseous and extraosseous components of aggressive bone tumors can be demonstrated with MR imaging (50,54-58). Intnaosseous assessment includes estimation of intramedullary extent, cortical involvement, and epiphyseal and joint space invasion and evaluation for same-bone and transanticular skip lesions (Fig i8). MR imaging is particularly well suited for the evaluation of the extraosseous component,
including
partmental
separation
intracom-
extnacompartmental 2ia), and delineation of ligamentous, tendinous, neumovascular bundle, and joint space involvement (S6-S9). The MR evaluation may facilitate decisions concerning limb salvage versus amputation, improve surgical confidence, and permit reliable assessment of patient prognosis. The development of adjuvant and
disease
from
of
(Figs
a
Ra1in1nav
20,
a.
b.
Figure
22.
(a) Ti-weighted
as in Figure
i8.
coronal
Although
there
has
sue mass, there is still extensive (b) Coronal T2-weighted image was demonstrated at biopsy, ullary portion of the bone. the same patient demonstrates ullary bone.
c. image been
obtained an
extensive
through reduction
tion
ing
and
signal
assessment
enhancement of gadopentetate
in
the
same
patient
extraosseous
portion no
soft-tis-
of the bone.
residual
tumor
there are residual areas of high signal intensity within the med(c) STIR image (1,800/30; inversion time, 150 msec) obtained in the nonspecificity of the diffuse high signal in the intramed-
demonstration
of volume
femur
in the
abnormality within the intramedullary obtained in the same patient. Although
neoadjuvant chemotherapy for bone tumors has led to a greater need for diagnostic modalities that predict response. MR imaging has played a critical mole in evaluating bone tumors after preoperative chemotherapy and irradiation. This modality has been used to assess tumor response through estimachanges,
the
intensity
of residual
following dimeglumine,
areas
administration and
of
of
changes
in
the
phos-
phorus-3i MR spectmoscopic findings. A good tumor response has been fined as devitalization of more than 90% of tumor cells (60,61). Although this
percentage
quantitated ity, MR trends.
cannot
be
de-
accurately
uniformly with any modalevaluation may help in predictWhile
not
an
absolute
indi-
cator of histopathologic response, a decrease in tumor volume after therapy is the best indicator of a favorable meMay
1991
b.
Figure
23.
Transverse
brous
histiocytoma.
ficult
to
distinguish
al viable tumor. eas of enhancement the area of cystic
Figure
24.
nonenhanced
the
large
Transverse
has sharp
peritumoral
obtained
On
through
cystic
central
borders,
area
size,
of
image
and
no
edema.
sponse (accuracy > 75%) (60). In most responders, theme is a reduction in the extraosseous component, with meestablishment of intemmusculam fat planes (Fig 21) (60,62). The relative inelasticity of the med-
necrosis
This
diminished
highly ton
not
specific of
malignant
images,
the
fi-
it is dif-
more
peripher-
intensity.
T2 signal
intensity
nonsensitive
(67).
high with
(high but
signal but
response
tissues mom)
may
from
decreased
demonstrate times
component
(arrows)
and
per-
tumor
(b)
image (c) demonstrates peripheral This would guide the biopsy away
tons,
mit a decrease in size of the intmaosseous component on MR images (Fig 22). In some cases, an apparent increased tumor volume may be associated with favorable histologic response (63). This finding is related to probable
ullany
in a boy with
T2-weighted
amfrom
any pulse sequence may be related to the sampling time (following therapy) and tissue heterogeneity. Ti relaxation values have been uniformly disappointing in predicting tumor response. T2 signal intensities have been vanable. The early tumor response has included replacement of tumor by a watery myxoid matrix and granulation tissue (64). Early fibrosis in this group consists primarily of fibmoblasts, vascular endothelial cells, and little collagen deposition. Each of these tissue types contributes to increased signal intensity on a T2-weighted image (63,66). This increased signal intensity is difficult to differentiate from recurrent tumor. “Late” fibrosis results in decreased extracelluiam water, increased binding of intracellular water to macromolecules, and high concentrations of collagen. These components result in a paucity of cells and water, hence few mobile pro-
thigh in a girl aggressive synolesion (am-
small
thigh
(a) and
Ti-weighted tumor tissue.
T2-weighted
the distal proved well-defined
the distal
Ti-weighted
A gadolinium-enhanced indicating viable necrosis.
obtained through with histologically vial sarcoma. The
row)
images
C.
STIR
Ti
sensitivity have
little
for
residual (Fig
(8). The role of gadopentetate mine in follow-up of bone not
been
completely
dimeglutumors has
defined.
Preopem-
Signal intensities may have some utility in tumor follow-up, although theme is disagreement about the value of these measurements (62-65). Responses to chemotherapy and irradiation are time dependent and vary with
atively, this agent has had a limited mole in determining biopsy sites in necrotic tumors (Fig 23) (60). Following chemotherapy and irradiation, gadopentetate dimeglumine has played an even more limited mole (68-70). As with STIR imaging, contrast enhancement is highly sensitive but nonspecific. Viable tumor, vasculanized granulation tissue,
the
and
necrosis
and
hemorrhage
within
the
tumor.
cell
type
general, py
the
is tumor
edema) and
first, finally
Volume
and
specific
response
tumor
necrosis
(±
then
granulation
fibrosis.
179
therapy. of
a
Number
In to
hemorrhage,
Shortcomings
2
hanced.
thera±
tissue, with
inflammatory
changes
Dynamic
studies
strated
some
promise
tumor
tissue
types,
tent,
worrisome
in
but overlap
all have
are
en-
demon-
characterizing
theme between
is persis-
nal-intensity
represents with time
space-occupying
residual following
Soft-Tissue
mass
tumor increases therapy.
Tumors
capability
of
relaxation
specificity
defined.
22)
resolution T2
being
From a practical standpoint, posttherapeutic MR evaluation should indude Ti- and T2-weighted sequences. Low signal intensity with both sequences indicates a small likelihood of residual or recurrent tumor. Increased signal intensity on T2-weighted images may represent posttherapy changes or residual tumor. If a discrete mass is not demonstrable, tumor is less likely. At times, the initial postthemapy image is used as a baseline examination. Resultant focal areas of high signal intensity are noted and followed on subsequent studies. The likelihood that a high-sig-
tu-
sequences
and
still
The role of plain radiography in evaluation of soft-tissue masses is limited to situations in which adjacent bone involvement is suspected. MR imaging is considered, in most cases, to be the initial imaging modality of choice. The
indica-
contrast
long
is a
benign and malignant lesions. There has been little agreement about the mole of P-3i MR spectroscopy in tumor follow-up (7i-7S). Rapidly evolving and variable techniques have resulted in contradictory data. The litenatune has indicated a nonuniformity in localizing techniques, a relatively small, heterogeneous group of tumors studied, and varying sampling intervals. The evolution of such multivoxel techniques as one-dimensional chemical shift imaging has resulted in some optimism (71). Early attempts to chamactemize phospholipid membrane-related peaks (phosphomonoesters, phosphodiestems) have been successful (71-76) and show a decrease in these peaks with successful therapy. These values and measurements of inorganic phosphate and phosphocreatine signal intensities may provide clues to help predict tumor response. The mole of MR spectroscopy in this group of patients is
of
MR
imaging
to
demon-
strate the presence or prove the absence of a mass cannot be underrated. This modality offers a 100% negative predictive value in cases in which softtissue masses are suspected. MR imaging may help in diffenentiating benign from malignant masses in more than 90% of cases (SO). Benign masses are generally sharply defined, sometimes encapsulated, homogeneous, and void of penitumoral edema (59,77,78).
Malignant
demonstrate margins,
indistinct, inhomogeneous
sity,
penitumomal
and
masses
frequently
infiltrating signal edema
inten-
(59,78).
Unfortunately, theme is overlap tween these groups. In many imaging is limited to predicting
Radiolov
becases, MR domi-
a
355
Figure
a.
b.
Figure
25.
weighted at the
(a) Radiograph
image joint
line
depicts and
of a lateral
the fracture
condyle
line.
There
even
infiltrating ing
when muscle
fascial
planes.
the or
hemangioma bone
Finally,
or
is is cross-
atrophy
on
hypoplasia of surrounding musculature can be seen in pediatric soft-tissue hemangiomas. Phleboliths are not readily identified on MR images, and therefore, plain madiogmaphs are a useful supplement to the MR evaluation. 356
a
Radiology
Sagittal
gradient-echo
image
of
fracture
(Milch
is rotation
type
and
II).
(b)
Coronal
displacement
Ti-
of the fragment
metaphysis.
nant histopathologic composition mathem than histologic diagnosis, and biopsy is often needed (Fig 24). On occasion, MR imaging may be melatively specific. Certain characteristic lesions exist, including lipomas, hemangiolymphangiomas, hematomas, subcutaneous fat necrosis, and popliteal cysts. In these instances, biopsy may be obviated (77). A lipoma will typically be seen as a well-defined, circumscribed lesion of the same signal intensity as subcutaneous fat. Septations within the lesion can be prominent, but theme is usually a lack of surrounding edema. The MR appearance of pediatric muscular hemangioma has recently been reported (79). Hemangiomas most often appear heterogeneous and are typically seen as intenmediate signal intensity on Tiweighted images with increased signal intensity on T2-weighted images. A serpentine lesion appearance is typical. The presence of fat within the lesion is highly suggestive of hemangioma, since the matrix of hemangioma is eithem fat or fibrous tissueoand few pediatmic tumors contain significant amounts of fat. However, the absence of a fatty matrix does not exclude the diagnosis of hemangioma. There is a lack of edema in the surrounding soft tissues,
26.
a posttraumatic physeal bone bar. The highsignal open physis is seen anteriorly. The posterior closed physis and the anterior convex bowing deformity are appreciated.
PERIARTICULAR IN
and late
DISORDERS CHILDREN
Most applications of MR imaging in around the joints of children meto trauma: acute injuries, chronic
stress,
and
old
are unique also occur most often childhood section.
Acute
injuries.
Some
disorders
to children; other injuries in adults. The entities that induce symptoms during will be discussed in this
Fractures
Management of acute fractures depends on the presence of displacement or notation of fracture fragments and whether there is dislocation at a joint. Most fractures involving a joint are meduced and pinned if there is more than 2 mm of displacement at the joint. In young children, delineating a fracture on a plain radiograph may be difficult, since the large amount of cartilage present is not seen. Elbow fractures can be particularly complex, and arthmogmaphy
can
be
required
for
fracture
delin-
eation and characterization. If alignment is in question, ing
is our
ing
complex
preferred
method
intraamticular
MR of
imag-
evaluat-
fractures
and unstable fractures after closed meduction. Ti-weighted or gradient-echo sequences will define bone and cantilage and allow accurate assessment of both the bony and cartilaginous components of the fracture as well as the precise alignment of bone and cartilaginous fragments (Fig 25).
Figure the
27.
knee
ment
Sagittal shows
of
the of
the
bone
fluid
cartilage
and
A highline
fragment
of frag-
dissecans. synovial
rounding
image
nondisplaced
osteochondritis
signal-intensity ture
Ti-weighted
a loose,
sur-
indicates loosening
fracof
the
piece.
Physeal
Injury
One
to
involve damage plate,
two
percent
the physis to a portion with
a resultant
bar. A physeal growth at the shortening. the less
than
physis,
If a bone
there
will
left
to allow
of
bar be
the can
bone
the
amount
develop
physis bar total be
as
continues
to
accounts areas
mesected
sufficient further
that
further bone
may
open 50%
the
determine
physeal
Deformity (80).
fractures
bar prevents site and causes
remaining
grow
of
result in permanent of the growth
normal bone
for of
the
and physis
growth.
of physis
To
in-
May
1991
pair. This can make interpretation of signal within the peripheral meniscus on postthenapeutic MR evaluation unreliable (88). Deutsch et al have shown that grade III signal may persist as long as 27 months after an injury despite healing confirmed on follow-up amthroscopic examinations (88). Persistent signal intensity at the site of previous injuries
b.
Figure 28.
Bilateral discoid lateral menisci seen in coronal and (b) left knees. On the right, there is increased
(a) right coid
lateral
discoid
meniscus.
meniscus
A torn is seen
and
on
the
macerated left.
No
meniscus discrete
volved, MR mapping can be performed (81). Images should be acquired pempendiculam to the deformed physis in two planes
and
will
show
interruption
of
the low-signal-intensity physis on Tiweighted images or high-signal-intensity physis on T2-weighted and gradient-echo images. The physeal line is lost
when
a complete
bone
ban
devel-
ops (Fig 26). If the growth plate is damaged but not closed, the physeal line will be distorted but the signal intensity will remain normal. Oblique growth lines indicate asymmetric growth across the physis.
Osteochondritis
Dissecans
Osteochondnitis dissecans is considemed a traumatic lesion that occurs most often at the knee, the ankle, and the elbow. The abnormalities occur at the sites
of
impact
for
these
joints
(82-84).
Irregularity of the nonarticulating postenor aspect of the condyles should not be mistaken for osteochondral lesions (85). Treatment of osteochondral fractures varies with lesion severity. Complete displacement of the osteochondral fragment from its site of origin requires removal of the loose body. If the fragment
is not
displaced
cartilage is cracked fragment may be moved, or treated Treatment varies dral fragment is lying cartilage is will
drill
flow
and
choose Lesion should planes: images weighted Ti-weighted the bone
Volume
such
but
lesions
promote
the
overlying
on fissured, the pinned in place, meconservatively. when an osteochonin place and the overintact. Some surgeons to
increase
healing.
blood
Others
to treat them conservatively. staging with MR imaging be done by imaging in two T2-weighted or gradient-echo in at least one plane and Tiimages in the other. On the or proton-density image, defect is delineated and the
179
a
Number
2
was
tear
was
gradient-echo signal intensity found seen
images within
at surgery. at
MR
of the the dis-
The
thickened
examination.
overlying cartilage assessed. Loss of signal intensity in the articular cartilage on Ti-weighted images indicates degeneration. At arthnoscopy, the cartilage will appear intact but will be soft and spongy when probed. High-signal-intensity synovial fluid or granulation tissue detected around the bone defect on T2weighted on gradient-echo images mdicates a crack or fissure has occurred around the fragment and therefore the fragment is loose (Fig 27). At surgery, the lesion may have the appearance of a “linoleum flap.” A crack or fissure of the cartilage only without loosening of bone fragment will best be determined on T2-weighted images, since fluid cannot always be distinguished from cartilage on gradient-echo images.
Internal Deranement, and Tendon Injury
in
Meniscal
injuries
children
and
common that
Ligament, are
may
not
become
as participation
result
in
a high
uncommon even
degree
of joint
stress at an earlier age accuracy of MR imaging
increases. in the
tion
with
of
menisci
more
in activities
is 95%,
The evalua-
a false-neg-
ative mate of 4.8% (sensitivity, 95%; specificity, 91%). For the anterior cruciate ligament, the overall accuracy is 95%. T2-weighted sequences are associated with greater sensitivity, specificity, and accuracy than are Ti-weighted sequences for the evaluation of anterior cruciate ligaments; the false-negative mate approaches 0% (86,87). In children, horizontal, linear high signal intensity will be seen in the region of the chondroid matrix. This is a normal finding and does not represent degenerative change. Because
of
the
peripheral
blood
sup-
ply, a tear in the outer third of the meniscus may heal with conservative management as well as operative me-
may
account
for
some
reported
cases of disagreement between MR and arthroscopic findings. Theme is a spectrum of normal MR appearances after partial meniscectomy (89). Standard MR criteria can be used to diagnose tears in the absence of marked contour irregularity; however, the diagnosis of tears of segments with marked contour irregularity must be made cautiously, since this irregularity can mimic a tear and may not be predictive of an arthroscopically visible tear. Ligament and tendon injuries are well shown with MR imaging (90). An imaging plane parallel to a large tendon such as the patellar tendon will adequately show the integrity of the tendon. Sections perpendicular to small tendons and ligaments will more accumately reveal abnormalities in these structures. Fluid in tendon sheaths and within
the
nitis.
Fraying
fibers
tendons
is seen
Discoid
is seen
or rupture with
partial
with
tendi-
of the
tendon
teams.
Meniscus
The discoid meniscus occurs developmentally when the meniscus fails to perforate centrally, resulting in a slablike appearance instead of the normal semilunar configuration. It occurs almost exclusively in the lateral compartment and is prone to easy tearing (Fig 28a). In the young child, it may cause pain and instability and can elicit snapping on clunking on examination. Indirect signs of a discoid meniscus on radiogmaphs include a high-riding fibula,
hypoplastic
lateral
condyle,
and
widened lateral joint compartment. On MR images, asymmetric meniscal height of more than 2 mm, as well as three or more “bow ties” on S-mmthick contiguous sagittal images, has been described as diagnostic of a discoid meniscus (91). The complete slab can be seen on coronal images and is the
most
agnosis
reliable
(Fig
way
to
confirm
the
di-
28).
Legg-Calv#{233}-Perthes Avascular Necrosis
Disease!
In advanced stages of Penthes disease, MR imaging is useful for the evaluation of the thickness and shape of nonosseous structures such as the femoral and acetabulam cartilage. This modality may also provide positional evalRadiolo2vc7
Figure the
29.
hips
disease.
Coronal
in a boy There
Ti-weighted
with
image
of
Legg-Calv#{233}-Perthes
is complete
loss
of
signal
and
collapse of the left femoral epiphysis. Thickening of both the left femoral epiphyseal and the tilaginous
acetabular femoral
cartilage is seen. The head is not deformed,
and there is no loss of containment cated by the position of the labrum
car-
as indi(arrow).
b.
a. Figure clearly uation of the to determine
femomal head and loss of containment
subluxation.
These
findings
labrum and
are
same more
30.
Legg
demonstrate
Calv#{233}-Perthes
a cold
child shows subtle difficult to appreciate
disease
epipyhysis. decreased than
of the
right
femoral
(b) Ti-weighted
signal intensity the scintigraphic
epiphysis.
coronal
(a)
image
of the right abnormality.
Bone
scintigrams
of the hips
in the
femora! epiphysis, Radiographs were
which normal.
is
mdi-
rectly assessed on plain madiogmaphs but are otherwise seen only with amthrography. The decision to perform surgery
in
a child
with
advanced
Perthes disease depends on the severity of the femoral head deformity, the degree of labmal eversion, and the loss of containment with subluxation. MR abduction views of the hip will help determine reducibility, but the gantry size limits how much abduction can be achieved. The dynamics of the hip are somewhat better assessed with anthrography than with MR imaging. Most cases of Perthes disease are found at advanced stages. Seldom do we have the opportunity to make the diagnosis early. The typical MR appearance of Perthes disease is loss of signal intensity
within
the
femoral
epiphysis
on Ti-weighted images (Fig 29). The appearance may be variable, with patchy loss of signal intensity or only slight decrease in signal intensity (3). In some cases, the abnormality is subtle and the lesion, difficult to detect (Fig 30). Scintigmaphy can be more specific than MR imaging, and the moles of MR and scintigraphy for early diagnosis are not yet defined. At present they are complementary.
Arthritis Cartilage
thickness,
joint
358a_Radiology
Figure
b. 31.
sification
Proximal focal femoral deficiency of the femoral neck is seen on the
tamed through the left hip shows fracture. Marrow signal intensity and proximal surrounding
femur marrow
as a result seen on
of the magnetic gradient-echo
described as being useful in diffementiating synovial hypentrophy from joint effusion. The greatest value of MR imaging may be in evaluating response to therapy sooner than it can be detected clinically or radiographicaily.
Congenital
on the radiograph.
left
an intact cartilaginous is suppressed in the
effusion,
synovial hypertrophy, and subchondral cysts are all better evaluated with MR imaging than with any other modality (92,93). In the young child, radiographic assessment of cartilage loss is particularly difficult because of the large amount of growth cartilage present. Contrast enhancement with gadopentetate dimeglummne has been
-
a.
Disorders
Complex and late diagnostic cases of congenital dysplasia of the hip are often difficult to reduce and treat. MR imaging may be useful in evaluating and identifying the causes of failed reduction, such as a thickened ligamentum teres or an infolded labmum. Fatty
(Aitken (b) Coronal
type
femoral
neck,
ilium,
effect
of trabecular
tissue
is easily
identified
may
be a cause
tion
to complete
within
MR
does
not
require
verse
head.
spica
Other be well
cast
There on
is no MR
congenital delineated
several
surgical
me-
has been apit may be
reduction. or
Trans-
gradient-echo
aging can be performed tion to document position ral
a hip.
after
cast hip,
to confirm Ti-weighted
and
obstrucof
“melt”
of
acetabulum imaging
reduction
will
section. After a spica plied for an unstable necessary
bone
the
at
osobhead, on
femoral
of temporary
tissue and
Incomplete image
no evidence
ossified
pulvmnar
weeks
with
ischium,
susceptibility images.
Pulvinar
A). (a) gradient-echo
artifact
imaging
im-
without of the
sedafemo-
from
a
(94).
disorders with MR
may also imaging.
May
1991
In some forms of proximal focal femoma! deficiency, there may be a cartilaginous femonal neck that is delayed in ossifying. The cartilage is clearly defined with MR imaging when images are angled parallel to the femomal neck (Fig
14.
31).
15.
Parker et a! have described identification with MR imaging of the anterior tibia! tendon hypoplasia in clubfoot defommity (95). We have shown increased tibial cartilage thickness after external fixator distraction in a child with chondroectodemmal dysplasia. Evaluation of Madelung deformity and Blount disease for physeal injury and growth amrest has not shown a primary physeal abnormality. MR imaging will continue to play a dominant mole in the diagnosis and pretherapeutic, postthemapeutic, and follow-up evaluation of pediatric musculoskeletal disease. Further experience with this modality will likely bring additional applications of MR imaging for the evaluation of pediatric musculoskeletal disorders. U
with
advancing
ative 1932; Kricun sion: italy
response to stimuli. J Lab Clin Med 17:960-962. ME. Red-yellow marrow converits effect on the location of some so!bone lesions. Skeletal Radio! 1985;
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siona!
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May
1991
G. Moore,
MD
George
a
Pediatric
S. Bisset
O
tnast
44.146
a
Joints,
MR
infants
and
in
Soft
neoplasms,
tissues,
Radiology
1991;
studies,
40.1214
children,
the
past
decade,
resolution
of
components
soft
magnetic
tissue
res-
and
mus-
to that of any other imand fatty and cellular
of bone
marrow
PRIMARY BONE
can be
MR portant
pose
DISORDERS MARROW
OF
The
osseous
component
of
marrow is cancellous bone, which provides architectural support for the myeloid and fat cells. Hematopoietic marmow contains approximately 40% water, 40% fat, and 20% protein, while fatty marrow contains approximately 15% water, 80% fat, and 5% protein. Red marrow has a rich sinusoidal system, while yellow marrow is supplied chief-
ly by capillaries, walled I
From
ogy,
the
S-058,
Medicine, ment
Department Stanford
of Diagnostic University
Stanford,
CA
of Radiology,
94305
Children’s
cal Center, Cincinnati stitute of Radiology,
(C.S.B.); Washington
School
St Louis
of Medicine,
partment Hospital,
School, scientific
Northwestern
(S.C.M.);
Depart-
Hospital
Medi-
Mallinckrodt University
University
(J.S.D.).
assembly.
accepted January to S.C.M. “RSNA, 1991
From
Received
29.
MR Appearance Marrow
of
In-
(M.J.S.); and DeChildren’s Memorial
of Radiology, Chicago
Radiol-
School
Address
Medical
the
1990
January
reprint
RSNA 14, 1991;
requests
veins
venules,
and
MD
pelvis, including the are the areas screened
most frequently with MR imaging for primary disorders of marrow, since these areas contain a large percentage of red
marrow
5-mm-thick
throughout images
thin-
(6).
of Normal
The MR appearance of the marrow is dependent on the relative fractions of fat and water. Cortical and trabeculam bone produce very little detectable MR signal. Signal characteristics vary with sequences and technical parameters. This discussion will focus on the use of spin-echo sequences with Ti and T2 weighting.
life.
are
Sagittal
usually
ob-
tamed in the spine, while S-mmto 1cm-thick coronal on transverse images are preferred in the pelvis and proxi-
mal femoma. images, (repetition
For Ti-weighted
a pulse time
is preferred,
for
of 300-500/20 time msec) T2-weighted
im-
or greater images,
intensity
that
spin-echo
sequence msec/echo
while
a signal
than
imaging is recognized diagnostic technique
cells.
S. Donaldson,
The spine and proximal femora,
has
as an imfor evaluating bone marrow because it provides excellent spatial resolution, anatomic detail, and the unique ability to separate hematopoietic (red) marrow from fatty (yellow) marrow (1-6). Bone marnow contains three major components: osseous matrix, myeloid tissue, and adi-
179:345-360
James
Session
ages, 2,000-2,500/70 ferred. On Ti-weighted
a
40.34
a
Focus
Imaging’
imaged.
a
40.34
VER
cle is superior aging modality,
Arthritis, 40.70 #{149}Bone marrow, 40.455, 40.64, 40.65, 40.671, 40.833, 40.92 #{149} Bone marrow, MR studies, 40.1214 #{149} Bone neoplasms, MR studies, 40.1214, 40.34 a Children, skeletal system a Joints, diseases, 40.443, 40.78 #{149} Joints, injuries, 40.41, Neoplasms,
MR
MD
onance (MR) imaging has become increasingly important in the evaluation of pediatric musculoskeletal disease. The advantages of MR imaging in the evaluation of the pediatric patient are many: (a) There is no known deletenious biologic effect; (b) there is no mequirement for intravenous contrast agents; and (c) there is no ionizing madiation. In addition, spatial and con-
terms: 40.21,
40.48,
Special
J. Siegel,
Marilyn
a
Musculoskeletal
In a review of the indications and uses for magnetic resonance (MR) imaging of the pediatric musculoskeletal system, MR evaluation of conditions unique to the pediatric musculoskeletal system were emphasized. Indications for MR imaging of the pediatric musculoskeletal system include evaluation of bone marrow, neoplastic processes, and periarticular disorders. Index 40.144,
III, MD
RSNA
med marrow
equal
of muscle
is pre-
to
or
less
in the newborn
and
greater than that of muscle but less than that of fat in children and adults. On T2-weighted images, the signal in-
tensity
is increased
and
that of subcutaneous which has a short
has a signal
may
be close
fat. Fatty relaxation
Ti
intensity
similar
to
marrow, time,
to that
of
subcutaneous fat on Ti-weighted images. The signal intensity of fatty manmow is decreased slightly on T2-weighted images, resulting in decreased contrast between yellow and cellular marrow when compared with Tiweighted images. If there is a true manrow abnormality, focal areas of low signal intensity on Ti-weighted images have greater signal intensity than that of normal marrow on T2-weighted images. Contrast between red and yellow marrow can be enhanced by low-flipangle gradient-echo imaging, short-tau inversion-recovery (STIR) imaging, and chemical shift imaging (7-10). Fat sig-
nal is decreased
in STIR
and
chemical
shift trast echo
imaging, improving tissue conand lesion conspicuity. Gradientimaging is useful in the evalua-
tion
of paramagnetic
fication,
signal
and
intensity
Abbreviation:
substances,
hemorrhage
(ii).
of the marrow
STIR
=
short
tau
calciThe
reflects
inversion
re-
covery
345
Figure 1. Normal macroscopic conversion of hematopoietic to fatty marrow. The relative amounts of macroscopic red and fatty marrow are shown for different anatomic sites (13).
0
cii 0 0
5
10
15
20
30
40
50
60
70
Age (years)
the presence of surrounding
Conversion Marrow
and
possibly trabeculam
from
Red
the amount bone (12).
to Yellow
Bone marrow, a dynamic organ, changes composition during growth and development (Fig 1). Almost all marrow space in the neonate contains red marrow. Shortly after birth, conversion from med to yellow marrow begins and progresses from the appendiculam to the axial skeleton and from diaphysis to metaphysis in individual long bones (i3,i4). In anatomic sections, theme is complete conversion of marrow in the terminal phalanges by 1 year. Macroscopic fat is observed in the midshaft of the long bones by 12-14 years and in the metaphysis by 20 years of age. The adult pattern is reached by the age of 25 years (Fig 2). Ossifying cartilaginous epiphyses and apophyses are only briefly hematopoietic, undergoing rapid conversion to yellow marmow within 3-4 months after ossification commences (15). Knowledge of the normal MR appearance and distnibution of red and yellow marrow is mequined for accurate interpretation of abnormal bone marrow conditions. Four MR patterns of bone marrow signal and heterogeneity have been descnibed in the long bones: infantile, childhood, adolescent, and adult (16) (Fig 3). The infantile pattern is found in the 1st year of life and is characterized by homogeneous low-signal-intensity marrow in the diaphysis and metaphysis. In children aged 1-10 years,
higher
signal
intensity
is ob-
served in the diaphysis, reflecting conversion of med to yellow marrow. The adolescent pattern is noted in patients aged 11-20 years. In this age group, distal metaphyseal med marrow converts to yellow marrow, producing increased signal intensity in the distal metaphysis. The metaphyseal marrow is heterogeneous due to residual islands of red marrow. The adult pattern
346
a
Radiology
is generally
reached
by
25
years
of age
and is characterized by relatively homogeneous high signal intensity in diaphyseal and metaphyseal marrow. Occasionally, low-signal-intensity foci are noted due to the presence of dense trabecular bone and the physeal scar. In general, the appearance of yellow marrow on MR images occurs at a younger age than would be expected from macroscopic anatomic data (Fig 4). Overall, marrow signal intensity comelates better with the percentage of microscopic fatty marrow than with the fraction of macroscopic fatty marrow (16). The axial skeleton is a primary source of red marrow production. In the first 2 decades of life, the vertebral marrow is rather homogeneous except for linear areas of high-signal-intensity fatty marrow paralleling the basivertebral vein (17). On the basis of anecdotal evidence, the vertebral marrow should be of higher signal intensity than the adjacent disk on Ti-weighted images in children
aged
more
than
10 years.
Mar-
mow signal intensity lower than that of the adjacent disk suggests a diffuse hematopoietic disorder. The spectrum of conversion from med to yellow marrow in the clivus and calvaria has been reported (18). Marrow in the clivus and calvania has a uniform low-to-intermediate signal intensity on Ti-weighted images obtained in most infants aged less than 1 year. Between the
ages
of
1 and
7 years,
this
poietic marrow is converted low- and high-signal-intensity By age iS years, most patients mogeneous high-signal-intensity marrow. Homogeneous lowintermediate-signal-intensity
hemato-
to patchy marrow. have hofatty or low- to marrow
in the skull or in the region of the clivus should be considered abnormal in any child aged more than 7 years. The signal intensity of occipital, panetal, and frontal calvanial marrow in males tends to be somewhat greater than that in females during the 2nd decade only. Two normal patients in this
Figure 2. Normal distribution of adult marrow. Macroscopic red marrow resides in the vertebral bodies, flat bones, and proximal metaphyses of the femora and humeri (shaded areas). The remainder of the skeleton (white areas) contains primarily yellow marrow (6).
study
had
low-
intensity the
to
marrow
2nd
decade
peamance
of
patients
of
lie
limits.
aged
Four
less
region
pelvic
than
mediate of
In
10 years, tensity acetabulum.
Mild
heterogeneity anatomic
20
years,
ity
on
MR
tenor
ilium.
increased signal the years
of
increased
the
anterior
intensity pelvis
in
In
persons
at aged
these 11-
hetemogene-
is not
uncommon,
the
acetabulum
Marrow
signal with
seen
and
marrow
sites.
children
in-
ilium
observed
compared
1 and signal
moderate
marrow
inter-
1st year
between
be
in
to
in the
to
images
in ho-
low
may marked
particularly
of
aged in
of
have
skull.
intensity
is seen
outside
is relatively
children marrow
normal
marrow
the
marrow
signal
life.
two
of
med
ap-
in
1 year
marrow
mogeneous
into MR
percent
fatty
frontal The
the
marrow
high-signal-intensity the
calvamia so
occasionally
accepted
children
the
life,
calvamial
may
these
intermediate-signalin
in
and the
all
aged
an-
intensity
is
marrow
regions less
of than
10
(19).
May
1991
a. 3.
Bone
Marrow
d.
C.
b.
Figure
Normal MR patterns of appendicular marrow. (a) Infantile pattern: Coronal Ti-weighted image of the pelvis and left femur of a 1-year-old boy shows low signal intensity in the diaphysis and metaphysis, reflecting the predominance of hematopoietic marrow. The ossified femora! head is of higher signal intensity because it contains yellow marrow. (b) Childhood pattern: Coronal Ti-weighted image through the distal femur of a 6-year-old girl shows high signal intensity in the diaphysis as well as the epiphysis, reflecting the presence of yellow marrow. The metaphysis has a signal intensity greater than that of muscle but less than that of fat, reflecting a greater red marrow fraction. (c) Adolescent pattern: Coronal Ti-weighted image of the distal femur and proximal tibia of a 16-year-old boy demonstrates high signal intensity in the diaphysis, metaphysis, and epiphysis consistent with distal metaphyseal conversion of red to yellow marrow. The distal metaphyseal marrow is patchy, reflecting residual islands of hematopoietic marrow. (d) Adult pattern: Corona! Ti-weighted image of the pelvis and femora in a 26-year-old woman shows relatively homogeneous high-signal-intensity yellow marrow in the epiphyses and diaphyses. The linear foci of low signal intensity in the metaepiphyseal region of the proximal femora represent the closed physes. The signal intensity of the femora is greater than that of the ilia, reflecting the greater percentage of red marrow in the flat bones.
is not possible on the basis of the MR appearance alone but requires commelation with the clinical context. Iron overload may occur in chronic disorders of erythropoiesis, due to mecurrent hemolysis and frequent blood transfusions. Iron deposition occurs primarily in the liver, spleen, and bone marrow. In these cases, marrow signal intensity decreases on Ti- and T2weighted images (20). Marrow changes may be diffuse or focal (Fig 7).
Disorders
Hematologic disease that affects bone marrow can be divided into four groups: myeloid hyperplasia, marrow replacement, myeloid depletion, and myelofibmosis.
Myeloid
Hyperplasia
Increasing sis
may
demand
stimulate
marrow
for
for
hematopoie-
recruitment
red
of
marrow
This
phenomenon,
sion,
results
from
mias
(sickle
cell
yellow
production.
termed
meconvem-
severe
chronic
anemia,
Marrow Infiltration
thalassemia),
marrow replacement disorders, or cyanotic heart disease. The pattern of meconversion is opposite that of physiologic red-to-yellow marrow conversion (Fig 5). In severe anemias, the epiphyseal marrow, which is normally fatty, may
convert
On nal
on
tissue
images,
than
the
amounts and
subcutaneous
neoplastic
Volume
of cellularity may
be
a
less
greater
than
The is not specific and is of marrow replacement fat
(Fig
processes.
179
and
slightly
or slightly
to,
MR appearance identical to that by
sig-
similar
that of muscle. On T2images, the signal intensity to a variable extent, depend-
equal of
marrow and
Number
6).
Differentiation
2
to
of
both
red
and
yellow
cantly
different
among
marrow by malignant cells will result in intermediate to low signal intensity on Ti-weighted images and increased
groups relaxation nosing
signal
images
mission
diffuse
can help differentiate ease from hypemplastic
intensity
(3,21-23).
marrow.
is decreased
water,
than, that
red
Ti-weighted
intensity
or less weighted increases ing
to
Replacement
ane-
temization and assessment of extent of an abnormality suspected on the basis of marrow aspiration or other imaging studies, evaluation of focal areas of bone pain, and assessment of response to treatment. Ti relaxation times of marrow in leukemia have been reported (22) and may be useful in determining the stage of disease. These marrow relaxation times are significantly longer in children with active disease than in children with leukemia in remission or in agematched controls (Fig 9). T2 relaxation times of bone mammow are not signifi-
The
on
T2-weighted
changes
are
often
in leukemic infiltration, but focal involvement may also be seen, especially in acute myelogeneous leukemia (21). Metastases and lymphoma are usually focal, well-defined lesions (Fig 8), although the margins can be poorly defined if there is marrow edema associated with the lesions (24). Occasionally, there is replacement of the entire marrow by metastases. Although MR imaging is sensitive for
diagnosing
infiltrative
not a practical screening indications for its use
disease,
tool. include
Primary chamac-
it is
Myeloid
(22).
The data times may acute disease, in
patients
these
suggest be useful relapse, with
various
that Ti in diagand me-
leukemia
and
neoplastic disred marrow.
Depletion
Myeloid depletion is characterized by a hypocellular or acellulam marrow with primarily adipose cells and areas of fibrosis. Causes of myeloid depletion include drugs, toxins, viral infections, radiation therapy, and chemotherapy. On Ti- and T2-weighted images, untreated aplastic marrow demonstrates an increased signal intensity, similar to that of subcutaneous fat, reflecting the
Radiology
a
347
Carthage
24
20
12-14
7
Birth
J
Red
Birth
Yellow
Cartilage
Figure 4. row change
MR
appearance
with
macroscopic
age.
sections,
percentage
versus
The
signal
which
of microscopic
reflects fatty
anatomic
intensity
marrow
distribution.
of the marrow
the sensitivity marrow than
Yellow
on (Fig
Ti-
and
T2-weighted
images
ii).
In Gaucher disease, the marrow becomes infiltrated and replaced by glucocerebroside-laden cells as well as fibmosis. Marrow involvement usually follows the distribution of red marrow, occurs first in the spine and flat bones, and then progresses from proximal to distal in long bones, with sparing of the epiphyses. The abnormal tissue produces a low signal intensity on Tiand T2-weighted images (28-30). Acute and chronic marrow infamction, due to marrow packing, are complications of Gauchem disease. Acute bone infarcts are seen as focal areas of decreased signal intensity on Tiweighted images and increased signal intensity on T2-weighted images. Oldem, fibrotic infarcts appear as low-signal-intensity
weighted
a
appearance
and
is greater
to detection fatty marrow.
than
(b)
macroscopic
would
of fatty marrow. (Adapted from
be expected The MR reference
appearance of red and yellow marfrom examination of anatomic appearance correlates better with 14.)
75 0 cii 0 0
50
cc 25
Myelofibrosis is the result of replacement of normal marrow by fibrotic tissue. Although uncommon in childhood, it is most often the sequela of chemotherapy or radiation therapy for leukemia, lymphoma, or metastases on of Gaucher disease. Rarely, it is a primany process characterized by splenomegaly and diffuse stromal marrow meaction. Replacement of the marrow by fibrosis results in decreased signal in-
348
Red
100
Myelofibrosis
tensity
(a) MR
on MR images
of MR imaging with macroscopic
high fatty content and lack of cellular marrow (23,25,26). Myeloid depletion is particularly noticeable in the spine following radiation therapy, with increased signal intensity on Ti-weighted images (Fig iO). With successful treatment, areas of low signal intensity appear in the yellow marrow, representing islands of active red cells.
(27)
j
24
20
b.
a.
the
12-14
7
foci
images.
Radiology
on
both
Ti-
and
T2-
0 Time Figure 5. undergoes in a proximal
Response Therapy
of the
Reconversion
of yellow to red marrow. The first, followed by the appendicular sequence (13).
reconversion to distal
Marrow
ages, subtle
to
Radiation therapy, marrow transplantation,
chemotherapy, and multiple
transfusions
used
are
each
in
the
on
Ti-weighted
and
STIR
marrow marrow
while on T2-weighted images, patterns of inhomogeneity and
mottling
are
more
difficult
to
appreci-
ate.
treat-
ment of pediatric disease. Each of these treatment modalities may affect the appearance of pediatric bone marrow. The MR appearance of the lumbar spine marrow in the first few weeks following radiation therapy has been reported (31). Theme are no appreciable differences in marrow signal intensity on spin-echo Ti- or T2-weighted images between pmetherapy examinations and those performed at 10-14 days; however, on STIR images, increased signal intensity can be seen at 10 days, corresponding to the marrow edema that predominates at this stage. Within 3 weeks after radiation therapy, there is either an increase in central fat or a mottled appearance to the vertebral marrow
axial
im-
Two “late” marrow patterns on Ti-weighted images: either geneous, increased-signal-intensity vertebral marrow-reflecting ment of red marrow by yellow (32,33)-or
a second
pattern
are seen homoreplacemarrow of
central
increased-signal-intensity fatty and peripheral intermediate-signal-intensity
med
marrow
(31).
marrow
Occasionally,
the marrow may respond primarily with fibrosis. Further studies in children are needed to define both the appeamance of vertebral marrow months to years after radiation therapy and the early appearance of the appendiculam skeleton following radiation therapy. MR changes following chemotherapy
have
been
long bones spond with
reported
(34,35). The hyperplasia
primarily
in
the
marrow may meand fatty me-
May
1991
Figure
7.
Ti-weighted sagitin an adolescent with sickle cell anemia shows diffuse decreased marrow signal intensity. Signal intensity was also diminished on the T2-weighted im-
tal image
b.
a.
Figure 6. Reconversion in sickle cell anemia. (a) Ti-weighted coronal image of the distal extremities shows low-signal-intensity red marrow in the tibial diaphyses, metaphyses, and epiphyses. Patchy foci of high signal intensity in the metaepiphyseal region correspond to residual islands of fatty marrow. (b) On the T2-weighted coronal image, focal areas of high signal intensity in the marrow represent areas of acute medullary infarction. Acute infarct can be difficult to distinguish from osteomyelitis on the basis of MR images alone.
Iron
overload.
of the spine
age.
E
ALL
ALL
Relapsa
b.
a.
Figure 8. Hodgkin lymphoma in an 18-year-old man. (a) Ti-weighted coronal image obtamed through the pelvis and femora shows low-signal-intensity tumor, replacing the marrow in the proximal metadiaphysis of the right femur as well as in the right iliac crest. The left femur and ilium are normal for comparison. (b) On the T2-weighted image, the signal intensity in the femoral and iliac marrow increases slightly more than normal. Marrow infiltration is usually best depicted by shorter rather than longer pulse sequences.
placement, resulting creased-signal-intensity images.
After
the
in diffuse inmammow on transition
from
gions
MR
initial
congestive edema to fibrosis, the marmow may appear as low signal intensity on both Ti- and T2-weighted MR images and may be patchy or homogeneous.
red
Apparent marrow
reconversion following
chemothemapy gmessively intensity
Volume
may
of yellow to treatment with be
decreasing appearing
179
a
seen, marrow
first
Number
in
2
with
pro-
signal marrow
not
expected
be
flat
expected
hematopoiesis
bones) to regions to contain
(eg,
and occasionalthat would med
marrow.
In some patients, areas of osteonecrosis may develop, which is attributed to the use of steroids or cytotoxic drugs (35). Prospective studies describing the appeanance of pediatric lesions of the bone following the administration of either radiation or chemotherapy have not
me-
of
metaphysis, ly progressing
been
Marrow
performed.
transplantation
is an increas-
ALL RemIssion
Normal
Figure 9. Ti relaxation times in children with leukemia. Histogram of the Ti relaxation times of the vertebral marrow in patients with newly diagnosed acute lymphocytic leukemia (ALL), leukemia in relapse (ALL Relapse), leukemia in remission (ALL Remission), and normal age-matched controls. Marrow Ti relaxation times are markedly prolonged in children with active leukemia compared with children with inactive disease and age-matched controls. Standard deviations for the various groups are noted. (Reprinted, with permission, from reference 22.)
ingly
used
form
of
therapy
for
pediat-
nc disease. Following pretmansplantation ablation therapy, marrow cells are infused intravenously and are typically engrafted oven the next 3-4 weeks. The appearance of the vertebral marrow following transplantation in i2 children has been described and consists of a peripheral zone of intermediate signal intensity surrounding a central zone of high signal intensity on Tiweighted images (36). This alternating zone of intermediate and high signal
Radiology
a
349
a. Figure
b. 11.
pharyngeal
Marrow
fibrosis
carcinoma
in a 16-year-old
metastatic
to
the
girl, left
who
ilium.
received
(a)
radiation
Transverse
therapy
for
Tl-weighted
naso-
image
demon-
strates low signal intensity in the marrow of the left ilium (arrow) and the left half of the sacrum (arrowhead). (b) On the T2-weighted image, low-signal-intensity marrow persists in the left ilium (arrow), but increased-signal-intensity marrow is noted in the left half of the sacnum (arrowhead) as well as in the soft tissues adjacent to the ilium. Biopsy revealed fibrotic marrow in the left ilium and recurrent tumor in the sacrum and soft tissues.
Figure 10. Myeloid depletion in a 16-yearold boy who underwent radiation therapy
10 months previously for lymphoma metastatic to the lumbar spine. Sagittal Tiweighted image shows high-signal-intensity marrow in the lower lumbar spine, consistent with fatty replacement. The vertebral marrow outside the radiation port has a more normal intermediate-low signal intensity.
intensity is termed the “band pattern.” This band pattern is detected in almost all children within 90 days following transplantation. Pathologic comrelation of the band pattern shows a peripheral
zone
topoietic
cells
nipheral
of
nepopulating
corresponding
intermediate
hemato
signal
the
pe-
intensity
on MR images. The central zone of increased signal intensity corresponds to fatty marrow surrounding the basivertebmal vein (36). Following transplantation, loss of the band pattern and appearance of a diffuse low-signal-intensity homogeneous marrow may herald a relapse of disease in those children with hematologic malignancies. Further long-term studies are needed to determine whether loss of the band pattern can also represent a normal marrow pattern in the months to years following transplantation.
Marrow
Edema
Marrow eralized
edema response
is a nonspecific, of
the
marrow
gento
stress or injury. While the stimulus of and controlling factors in the initiation of edema are uncertain, it is known that the amount of extracellulam water
350
a
Radiology
Figure
12. Coronal Ti-weighted image of the distal femur in an 8-year-old girl with an osteoid osteoma of the distal right femur. Thickening of the cortex (arrows), which remains of low signal intensity, is seen surrounding the lesion. The low-signal-intensity marrow edema is extensive, with a sharp demarcation between normal and edematous marrow (arrowheads). The presence of marrow edema with thickening of the cortex and no evidence of soft-tissue edema or mass should suggest the diagnosis of osteoid osteoma (3).
Figure
13. left
girl.
The
marrow
farct
is the
row,
with
rim,
which
signal
fined
Ti-weighted
sharp margin between normal marrow (Fig defined and feathery. diagnosis of pediatric
with
a fairly
normal and ab12), or it can be illThe differential marrow edema
same
as
acute
trauma,
reflex
osteoid
osteoma,
“Transient”
been pain
in an
that
of
of
inmar-
bone.
from
edema and
94.)
due
to
ischemia,
chronic and
marin-
infection,
sympathetic
dystrophy, tumor. abnormalities
in children these in
(Re-
reference
osteoporosis,
In
the
low-signal-intensity
marrow
intensity
il-year-old
sclerotic
reported (37).
older the
surrounding
permission,
or
an of
intensity
“transient”
famction,
hip
(arrow) signal
represents
stress
have
and infarct
a serpiginous,
includes row
tibia
with
increases as a result of hypervasculamity and hyperperfusion. The increase in extmacellular water is most likely modulated by the severity of the hypervasculanity and hypemperfusion. The MR image will reflect this increase. Marrow edema is seen as low to intermediate signal intensity on Tiweighted images, which increases on T2-weighted, fat saturation, and STIR images. Marrow edema can be well degeographic,
lymphoma medullary
proximal
printed.
and
Known
therapy-induced
the
images
with
children,
low
femoral
head
eventually
solves,
reverting
to
marrow
signal
intensity.
coincides ment in
with documented the child’s clinical
on
me-
a normal
pattern This
of
reversion
improvecondition.
May
1991
particularly
sensitive
to
marrow
or
soft-
tissue abnormalities. Theme has been some suggestion that the finding of fluid surrounding the bone at ultrasound examination is specific for osteomyelitis; however, recent reports have shown that this finding is not specific for osteomyelitis. While madionuclide bone scanning may be sensitive for detection of osteomyelitis, it is probably
not
as sensitive
as
MR
aging. In one recent study, MR was positive in six of six patients, a.
b.
Figure
14. acute
with ischium
(a) Ti-weighted osteomyelitis
(arrow),
with
intercalation
fat
saturation
image
transverse is seen
throughout
head)
and
into
tis
fat
saturation
on
transverse of the right
the
the
right
soft
tissues.
image ischium. of
infection
obtained ischial
The
just
scintigmaphy
through the femoral Low signal intensity through
the
inferior
marrow,
extending
increased
signal
to the
head in a 2-year-old is seen within the
cortical
of a. High
through
the
intensity
(b) T2-weighted
bone.
plane
signal
cortical
is typical
boy right
intensity
bone
for
(arrow-
acute
osteomyeli-
images.
was
teomyelitis
is marrow signal
ed images specific marrow changes. Children with sickle cell anemia, Gaucher disease, or hematopoietic malignancies and those undergoing steroid therapy can all be first seen with medullary infarction. Differentiation between early acute medullary ischemia and transient marrow edema based on the MR appearance alone is not
Figure
15.
(200/i5,
Coronal
30#{176} flip
gradient-echo angle)
image
obtained
through
the distal femur in a boy with Ewing ma. The low-signal-intensity Codman gle (arrow) and the calcified Sharpey (arrowheads) extending through the sue mass can clearly be seen.
possible,
While sarcotrianfibers soft-tis-
sient
bone
some
unknown
are marrow
and
has
acute
Calv#{233}-Perthes diogmaphs mild
symptoms
disease)
by
would On
dence,
the
normal osteoporosis.
pain specific
basis MR
of
(low
tensity
Volume
a
that or
anecdotal of on images),
representing
seen The
gain
on
a signal of
the
diagnosis
sity
that
myelitis.
While
diatnic
osteomyelitis
me-
is equal
is increasingly
to
used
evaluation most
of
cases
are
metaphyseal
in
osteo-
in
interface mal
marrow
Marrow become duration peniosteal
Theme
or
the
articular
epiphysis.
tive
for
tion
and
capsule of
the
earlier
reports
ing
was
of
evaluating
While
early
detection
peniosteal
CT
may of bone
reaction,
be
cortical
for
thickening,
Cortical
sensi-
seen
as
it is not
fat
be
and
pemios-
bone
and
evaluated or
edema,
bone with
will
usu-
transverse
associated
lesions width
is often of
spin-echo,
images.
pen-
with
be
thickening
on
with con-
lesions,
should
increased
saturation
method
evaluated
evaluated
nonaggressive
imag-
good bone
Cortical
with
bone
MR
While
infiltration
and
cortical
that
(42). musculoskeletal bone
best
severity
experience lesions
cortical can
MR imaging In pediatric the
the
a particularly
both
the ab-
infection.
cortical
either
images;
pemiosteal
with the
be
MR
or
teal reaction, further pediatric musculoskeletal that
destruc-
on
suggested
not
images.
in pacan
abnormal
of
cel-
pemiosteum
increases
reaction
encloses
metaphysis
associated
a be
abscess.
and
duration
may
by the time there will abnommali-
either
of cortical
be
the
defined.
osteomyelitis
firmed
in
abnor-
inflammation
be
cortex with
ally
ankle
the
and
poorly
soft-tissue
as
and
infection,
Usually, imaging, of soft-tissue
may
or
destruction.
shoulder,
of
normal
soft-tissue
be appreciated. child undergoes MR evidence
and
14).
is often
and
hip,
but
signal increases and margins better defined with increasing of infection. Surrounding
spread across the growth plate and involve the epiphysis, especially in infants and young children. The epiphysis can also be involved in joints such the
low images
abnormality,
course
between
osteal
can
of infection,
(Fig
the
pe-
infection
sig-
images.
Ti-weighted
MR
is increased
to the
of acute
confined
only
normality
usually
to increased
hours on
de-
Ti-weight-
T2-weighted
few
the
Early
The
unaffected
and
a portion
with-
be
tients
(Fig
will
intensity
marrow. MR imaging
both
in-
may
ty.
sclerotic
madiographs
marrow
surrounding
which
Ti-
plain
central
transient effu-
difficult
six
as the infection progresses and the time between the onset of infection and performance of an MR examination increases, increasing signal intensity will be seen on the T2-weighted images (41). On T2-weighted fat saturation and STIR images, the marrow signal inten-
likelihood
rim
hip signal
2
tu-
evi-
increased
Number
accom-
trauma,
intensity
T2-weighted
179
not
of a simple
images, on
The
be
intensity
the
a serpiginous
metaphysis,
show
symptoms
appearance
signal
of ma-
may
first
normal
the
cases
or
are
infection,
consists
weighted
In
of
acute
(38)
edema,
be
the
synovitis
(39).
marrow
other
associ-
(Legg-
degree
suggest
mor.
to
been
should of
panied
also
necrosis
pediatric
some
secondary
infarcts
of
with
on
normal on
In the
low-signal-in-
with
13).
tran-
osteoporosis
avasculam
transient
to
are
and
signal
ities,
that
aggressive
early
sion
edema
edema
with
due
stimulus.
Transient
ated
likely
entities
five
edema,
intensity
intensity
lulitis
bone changes
both
nal
to diagnose definitely, older infamcts have a much more typical appearance. These are seen as geographic abnormaltensity
These
since
seen on MR images as marrow edema. While early medullary infarction will be seen as an ill-defined region of low signal intensity on Ti-weighted images and increased signal intensity on T2weighted images, medullary infanctions usually become well defined and geographic in appearance fairly quickly (Fig 6). Depending on the cause, marrow infarction can be peniarticulam or present anywhere within the medullamy cavity.
in
patients (40). In addition, scintigraphy does not accurately define the full extent of infection, and it is sometimes difficult to separate soft tissue from bone infection (41). The earliest MR finding of acute oscreased
out
positive
im-
imaging while
the
black
STIR, This
can
Radiology
and be
seen
a
351
with
cortical
sions
buttressing
that
such
result
in
as osteoid
and
cortical
with
le-
thickening,
osteoma
(Fig
12).
Edema
of the cortical bone or involvement of the cortical bone by a pathologic process such as infection or intercalation of tumor through haversian canals will be seen as intermediate signal intensity within the normally black cortical bone. The MR appearance of peniosteal meaction has been described (42,43). On spin-echo MR images, peniosteal reaction can be appreciated as either intermediate signal intensity on Ti-weighted images that increases on T2-weighted images on low signal intensity on both Ti- and T2-weighted images (Fig 15). Peniosteal reaction that is low signal
intensity
on
both
Ti-
and
T2-
weighted images represents lamellam pemiosteal reaction. Complex peniosteal reaction, such as spiculated peniosteal reaction or lesions with new bone formation (such as osteogenic sarcoma), may not be appmeciated as calcified on MR images, since complex pemiosteal reactions comprise structurally disorganized bone embedded in a protein and/or tumor matrix.
Figure
16. Transverse proton-density image obtained through the distal a child with chronic osteomyelitis. cortical thickening is present, and course and depth of the sinus tract the cortex can be identified. Increased intensity
and
in
the
marrow
surrounding
musculature
represents
persistent
tion
will
reveal
abscess,
The
can
nal.
drainage. In healed bone marrow may
Pitfalls
in
the
evaluation
bone,
of
mined the
pemioste-
al reaction on MR images include partial volume averaging in regions of rapidly tapering bone and of cartilaginous epiphyses and muscle attachments, the presence of a soft-tissue mass adjacent to the bone, and postemion femonal hypemostosis. The MR examination should never be interpreted
with size
This
the
of
the
MR
as
ing
tion
of
image,
minimizing
necessary
low
signal
to
intensity
The
for
intensity
soft
images. intensity
In may
these
entities
sions
such
signal
both
Ti-
Areas as low
intensity
on
and
T2-
of active infecto intermediate
Ti-weighted
im-
ages, with increased signal intensity on T2-weighted images (41,44). The course and depth of sinus tracts can be appreciated within both soft tissues and contical
bone
(Fig
elitis,
the
often
well
ty,
theme
osteomy-
infection and
tissues
are
marrow
bone,
Soft
in
are
cavithe
soft
almost
in-
imaging
is useful
of
pediatric
osteomyelitis,
the
planning evaluating
sion
to
known
a
a role
for
MR
need
for
surgical
the surgical the response
therapy.
In
osteomyelitis,
Radiology
a case
in
fatty
The the
appropriate
presence
will
will
in
approach, of the of suspected
examina-
le-
child
marrow,
the
images
with
predom-
be
confined
the not
be and
to
cortical
the
bone,
accompanied
and by
joint
effusion
fractures
can
do
may
not
or
soft-tissue be
on The osteoid
as
and
involve
The
nidus
and
have
signal
bone images.
on
both When
Tistress
and
T2fractures
signal that
can of
of
the
shaft
(Fig
appearances: Ti-
decreased
low and
T2-
signal
and
in-
T2-weighted
signal images on
exten-
identified
increased
intensity
accom-
be
be
both
Ti-
the
which T2-weighted
often
on
Ti-weighted
intensity
and
increased
T2-weighted
im-
ages. Cortical
“edema”
has
osteoid
osteoma
(46).
in ence
of
sive
cortical of
or
no
should osteoma,
can
a
child
ed
the be
be
extensive.
presents of
is usually after cortical more
osteoid the plain
the
cortical
accompanied
by
edema this
clinical than
imaging
and
the
may
or
reason, computMR
imag-
modality
radiography,
if
symptoms
osteoma,
rather
abnormality easily
suggest
For
with
tomography,
ing,
be
pres-
exten-
thickening, marrow
not
the
and
edema
cortical
reported
While
osteoid
osteoma
little
been
thickening
marrow
diagnosis
choice
weighted
and
much can
both
or
at
in by
edema
images,
signal
osteoma
as decreased
a variety
on
low-signal-intensity
to cortical
frac-
setting,
Ti-
intensity
suggestive
perpendicular
stress
thickening,
osteoma
i2).
nonspecific “marrow edema.” They can be accompanied by extensive marrow edema, or they can be seen as a focal line
image of
osteoid
marrow
sive
may seen
pres-
be suggested,
both
accompanying
(45). also
of
appreciated
images,
marrow,
the
T2-weighted
clinical
images.
osteoid
are
and
diagnosis
cortical
panies
tures
involve
How-
low-signal-in-
should of
tensity
trabecular
le-
tumor.
bone
diagnosis
imaging
The
T2-weighted
aggressive or
the
the
MR
on
Stress drain-
on
In an older
on
distinguish
tume.
micmofmactume is best seen on Tiweighted images. In an infant or youngem child with predominantly hematopoietic marrow, a trabecular microfractune may not be appreciated on the Tiweighted images. These lesions will be seen as increased signal intensity on T2weighted images. Tmabeculam microfrac-
injury
the
imaging
MR
intensity
i7).
inantly
may
MR is also
assessing
352
the
in the
cortical
diagnosis
or
chronic
abnormal.
While
age, and
of
defined
(4i).
variably
In
margins
within
tissues
i6).
(Fig
more
cortical
line
marrow to
infection
suggest
weighted
on
images. be seen
ma-
plain
permission,
extensive
from as
intact
signal
intensity
weighted tion will
plain
mi-
a negative
difficult
of a perpendicular
signal
of a recent
by be
ence
diogmaphic examination. Chronic osteomyelitis can be chamacterized by areas of overgrowth of bone and sclerosis, which will be seen as low
benefit
trabecular
with with
ever,
by deposireturn
in
3.)
it can
heal tissues
mar-
a ski-
image.
extensive
a patient
surrounded
edema,
can
hu-
following
T2-weighted
(Reprinted,
tensity on
the an
in reference
intensity
the
on
represented
normal.
occasionally fat.
for
be deter-
boy
A region of low signal intensity the marrow on the Tiimage (arrow), which increased
weighted
are
for
osteomyelitis, the heal with scarring.
return
may
of
Ti-weighted proximal
within
to normal. Medullary trauma will also be accompanied by marrow edema. In children, tmabecular fractures or bone contusion will result in an ill-defined area of low to intermediate signal intensity on Ti-weighted images and increased
without
a 17-year-old
injury.
is seen
This
need
approach
also
and T2-weighted marrow signal
completely
row
the
incision
appears
both Tichildren,
foci
indicating
drainage
lamellam
of
signal
infection.
well-defined
marrow
drainage.
in
merus
from
surgical
protons
17. Oblique coronal obtained through the
radiograph.
surgical
the
Figure image
crofracture
which do not resonate during clinical proton MR imaging, these protons are free to resonate and will result in sig-
Unlike
MR femur in Marked the through signal
of
since and
nidus
may
appreciated.
May
1991
PEDIATRIC MUSCULOSKELETAL TUMORS Bone
Figure 19. Transverse proton-density fat saturation image obtained through the left side of the chest of a 7-year-old boy with a soft-tissue abscess. A focal region of highsignal-intensity infection is seen (arrow), and edema extends anteriorly around the chest wall.
seen on “transient,” Figure
18. Coronal Ti-weighted image obtamed through the distal femur in a boy with primary bone lymphoma. Note the sharp delineation between intramedullary tumor and normal fatty marrow (arrow). Also demonstrated is transphyseal extension
of tumor
into
the distal
heads). The distal with intercalation
epiphysis
(arrow-
cortical bone of tumor.
is thinned,
Finally, diffuse medullamy tumors, such as Ewing sarcoma or lymphoma, can be difficult to distinguish from fuse marrow edema. Intramedullary mom
is usually
normal
sharply
marrow,
companying
demarcated
and
there
endosteal
thinning,
and
diftufrom
is often
cortical
involvement
ac-
erosion, of cortical
the
MR examination may be secondary to mild osteopo-
rosis,
infarction,
ulan
micmofnactume
trauma or
such bone
as
trabec-
contusion,
or reflex sympathetic dystrophy. The presence or absence of soft-tissue
edema
is similarly
important
margins,
in
the
differential diagnosis of marrow edema. Recent studies have suggested that more aggressive processes are accompanied by marrow edema, while slowgrowing tumors and less aggressive processes are accompanied by less softtissue edema (47). If there is extensive soft-tissue edema surrounding an area of marrow edema, acute trauma and acute inflammation should be considemed. If theme is a moderate to small amount of edema surrounding the marrow abnormality, slow-growing tumor, chronic infection, and subacute trauma
bone (Fig 18). A soft-tissue mass should suggest either tumor or infection. When a marrow abnormality is identified on a pediatric MR examination, the clinical history, physical examination, and plain radiogmaphs are pivotal in the differential diagnosis. If the marrow edema is pemiarticular, one can
should
consider
Hemorrhage caused by acute trauma can also masquerade as a soft-tissue mass. MR imaging is the examination of choice in the evaluation of soft-tissue infection. On Ti-weighted images, softtissue infection will be seen as low to intermediate signal intensity with increased signal intensity on T2-weighted images (Fig i9). The adjacent marrow will be normal unless there has been tmanscortical spread. In cases of
the
crofracture infarct.
diagnosis
and If the
of
trabeculam
peniarticulam marrow
mi-
medullary
edema
is diffuse
and well defined, one can consider infection, osteoid osteoma, and tumor. Finally, the presence of cortical thickening,
soft-tissue
edema,
and
a soft-tissue
mass can be helpful in the differential diagnosis of marrow edema. If the cortex is eroded or theme is increased tex
signal
intensity
indicating
gressive
within
intercalation process
the of
through
the
an
corag-
cortical
be
rounding
row
considered.
If theme
soft-tissue
edema
represent
edema,
identified
edema,
tumor
and
cellulitis,
infection
the
are
cal
diagnostic
Volume
179
a
Number
the
marrow
2
edema
intensity. signal
that
signal
likely
to
bone
con-
signal images
intensity
conform
on
to the of
fasciitis.
likely.
intensity
while abscess can be displace normal tisareas of fluid signal
Intermediate
on Ti-weighted
most
abnormal
can be ill defined, well defined, will sues, and can have
is normal,
sun-
mar-
tusion, stress fracture, or medullany infanction. Finally, if there is a soft-tissue mass associated with the abnormality,
bone, tumor, infection, and aggressive osteoporosis are more likely. If the cortical bone is thickened but maintains a signal void on both Ti- and T2-weighted images, diagnosis of osteoid osteoma, stress fracture, and chronic infection should be considered. If the cortibone
is more
“transient”
is no the
and
intensity increased
T2-weighted
fascial
images
planes
Tumors
The evaluation and treatment of musculoskeletal tumors in the pediatric population has changed dramatically in recent years, partially as a result of significant developments in imaging studies. The advent of MR imaging and the refinement of limb-salvage surgical techniques have contributed significantly to improved survival (48-50). The role of imaging in bone tumors includes lesion detection and characterization, staging, treatment planning, and postthenapy follow-up. Plain radiography remains a reliable method for predicting the histopathologic nature of a specific skeletal lesion. Detection and characterization of a skeletal lesion rely on localization of a lesion, assessment of lesion extent and
are
evaluation
of
cortical
destruc-
tion and pemiosteal reaction, presence of adjacent soft-tissue mass, and identification of lesion matrix. These findings can usually be accurately assessed with plain radiography, and a working differential diagnosis can be generated. Currently, the role of MR imaging in diagnosing a specific lesion is somewhat limited. The technique, although sensitive, is nonspecific. Early attempts to predict lesion histologic findings at MR imaging have been disappointing (Si,S2). Although this shortcoming may be partially related to the nonspecificity of proton imaging, an even greater drawback may be the relative lack of experience with MR imaging (Fig i5). As experience and scientific research in the MR appearance of bone lesions
accumulate,
the
predictive
val-
ue of this modality may improve. To determine the need for further imaging studies in the case of a pediatnc skeletal lesion, the plain radiograph is first evaluated. A “do-no-evil” lesion (eg, fibrous cortical defect) requires no further evaluation. Some lesions (eg, osteochondromas)
may
require
follow-
up radiography and possibly MR evaluation, particularly with clinical changes in size or symptoms. On the MR examination, malignant degeneration of an osteochondroma to a chondrosarcoma is characterized by disruption of the cartilaginous
cap
and
presence
soft-tissue mass that is contiguous the osteochondroma. This mass as intermediate signal intensity weighted images and increased intensity on T2-weighted images. There has been some suggestion the degree of thickening of the laginous cap can be suggestive lignant nous
cap
change.
In
more
than
adults,
of
a
with is seen on Tisignal that cartiof ma-
a cantilagi-
3 cm
thick
RadioIoQv.a
is con-
Figure
20.
obtained
Transverse through
with osteosarcoma. tercalated through tibial
cortex
heads). This disease.
proximal
image tibia
Although the anterior
(arrow), by the indicates
be contained
Ti-weighted
the
in a girl
tumor has inaspect of the
the tumor appears periosteum (arrowintracompartmental
to
a.
b.
Figure 21. (a) Transverse T2-weighted with primary bone lymphoma. There sive extracompartmental quence 4 months
planes
and
after
disease. the initial
no evidence
image
obtained
are obliteration
(b) Follow-up image image demonstrates
of significant
residual
through
the
distal
of intermuscular
thigh
in a boy
fat planes
obtained with reestablishment
an
and
exten-
identical pulse of intermuscular
sefat
tumor.
sidemed suspicious for malignant degeneration (53). However, thick camtilaginous caps are generally seen in children, and there have been, to our knowledge, no prospective studies measuring the normal thickness of the cartilaginous cap in pediatric osteochondroma. Therefore, it is less likely that this criterion will be useful in the evaluation of possible malignant degeneration in pediatric osteochondroma. Other lesions (eg, large unicameral or aneurysmal bone cysts) require cunettement with possible bone grafting to prevent pathologic fractures. Finally, when biopsy and possible surgical memoval of a lesion are deemed necessany,
MR
imaging
plays
a crucial
role
in
staging and treatment planning. The goals of such planning relate to preserving limb function and minimizing the chances of local recurrence. Both the intmaosseous and extraosseous components of aggressive bone tumors can be demonstrated with MR imaging (50,54-58). Intnaosseous assessment includes estimation of intramedullary extent, cortical involvement, and epiphyseal and joint space invasion and evaluation for same-bone and transanticular skip lesions (Fig i8). MR imaging is particularly well suited for the evaluation of the extraosseous component,
including
partmental
separation
intracom-
extnacompartmental 2ia), and delineation of ligamentous, tendinous, neumovascular bundle, and joint space involvement (S6-S9). The MR evaluation may facilitate decisions concerning limb salvage versus amputation, improve surgical confidence, and permit reliable assessment of patient prognosis. The development of adjuvant and
disease
from
of
(Figs
a
Ra1in1nav
20,
a.
b.
Figure
22.
(a) Ti-weighted
as in Figure
i8.
coronal
Although
there
has
sue mass, there is still extensive (b) Coronal T2-weighted image was demonstrated at biopsy, ullary portion of the bone. the same patient demonstrates ullary bone.
c. image been
obtained an
extensive
through reduction
tion
ing
and
signal
assessment
enhancement of gadopentetate
in
the
same
patient
extraosseous
portion no
soft-tis-
of the bone.
residual
tumor
there are residual areas of high signal intensity within the med(c) STIR image (1,800/30; inversion time, 150 msec) obtained in the nonspecificity of the diffuse high signal in the intramed-
demonstration
of volume
femur
in the
abnormality within the intramedullary obtained in the same patient. Although
neoadjuvant chemotherapy for bone tumors has led to a greater need for diagnostic modalities that predict response. MR imaging has played a critical mole in evaluating bone tumors after preoperative chemotherapy and irradiation. This modality has been used to assess tumor response through estimachanges,
the
intensity
of residual
following dimeglumine,
areas
administration and
of
of
changes
in
the
phos-
phorus-3i MR spectmoscopic findings. A good tumor response has been fined as devitalization of more than 90% of tumor cells (60,61). Although this
percentage
quantitated ity, MR trends.
cannot
be
de-
accurately
uniformly with any modalevaluation may help in predictWhile
not
an
absolute
indi-
cator of histopathologic response, a decrease in tumor volume after therapy is the best indicator of a favorable meMay
1991
b.
Figure
23.
Transverse
brous
histiocytoma.
ficult
to
distinguish
al viable tumor. eas of enhancement the area of cystic
Figure
24.
nonenhanced
the
large
Transverse
has sharp
peritumoral
obtained
On
through
cystic
central
borders,
area
size,
of
image
and
no
edema.
sponse (accuracy > 75%) (60). In most responders, theme is a reduction in the extraosseous component, with meestablishment of intemmusculam fat planes (Fig 21) (60,62). The relative inelasticity of the med-
necrosis
This
diminished
highly ton
not
specific of
malignant
images,
the
fi-
it is dif-
more
peripher-
intensity.
T2 signal
intensity
nonsensitive
(67).
high with
(high but
signal but
response
tissues mom)
may
from
decreased
demonstrate times
component
(arrows)
and
per-
tumor
(b)
image (c) demonstrates peripheral This would guide the biopsy away
tons,
mit a decrease in size of the intmaosseous component on MR images (Fig 22). In some cases, an apparent increased tumor volume may be associated with favorable histologic response (63). This finding is related to probable
ullany
in a boy with
T2-weighted
amfrom
any pulse sequence may be related to the sampling time (following therapy) and tissue heterogeneity. Ti relaxation values have been uniformly disappointing in predicting tumor response. T2 signal intensities have been vanable. The early tumor response has included replacement of tumor by a watery myxoid matrix and granulation tissue (64). Early fibrosis in this group consists primarily of fibmoblasts, vascular endothelial cells, and little collagen deposition. Each of these tissue types contributes to increased signal intensity on a T2-weighted image (63,66). This increased signal intensity is difficult to differentiate from recurrent tumor. “Late” fibrosis results in decreased extracelluiam water, increased binding of intracellular water to macromolecules, and high concentrations of collagen. These components result in a paucity of cells and water, hence few mobile pro-
thigh in a girl aggressive synolesion (am-
small
thigh
(a) and
Ti-weighted tumor tissue.
T2-weighted
the distal proved well-defined
the distal
Ti-weighted
A gadolinium-enhanced indicating viable necrosis.
obtained through with histologically vial sarcoma. The
row)
images
C.
STIR
Ti
sensitivity have
little
for
residual (Fig
(8). The role of gadopentetate mine in follow-up of bone not
been
completely
dimeglutumors has
defined.
Preopem-
Signal intensities may have some utility in tumor follow-up, although theme is disagreement about the value of these measurements (62-65). Responses to chemotherapy and irradiation are time dependent and vary with
atively, this agent has had a limited mole in determining biopsy sites in necrotic tumors (Fig 23) (60). Following chemotherapy and irradiation, gadopentetate dimeglumine has played an even more limited mole (68-70). As with STIR imaging, contrast enhancement is highly sensitive but nonspecific. Viable tumor, vasculanized granulation tissue,
the
and
necrosis
and
hemorrhage
within
the
tumor.
cell
type
general, py
the
is tumor
edema) and
first, finally
Volume
and
specific
response
tumor
necrosis
(±
then
granulation
fibrosis.
179
therapy. of
a
Number
In to
hemorrhage,
Shortcomings
2
hanced.
thera±
tissue, with
inflammatory
changes
Dynamic
studies
strated
some
promise
tumor
tissue
types,
tent,
worrisome
in
but overlap
all have
are
en-
demon-
characterizing
theme between
is persis-
nal-intensity
represents with time
space-occupying
residual following
Soft-Tissue
mass
tumor increases therapy.
Tumors
capability
of
relaxation
specificity
defined.
22)
resolution T2
being
From a practical standpoint, posttherapeutic MR evaluation should indude Ti- and T2-weighted sequences. Low signal intensity with both sequences indicates a small likelihood of residual or recurrent tumor. Increased signal intensity on T2-weighted images may represent posttherapy changes or residual tumor. If a discrete mass is not demonstrable, tumor is less likely. At times, the initial postthemapy image is used as a baseline examination. Resultant focal areas of high signal intensity are noted and followed on subsequent studies. The likelihood that a high-sig-
tu-
sequences
and
still
The role of plain radiography in evaluation of soft-tissue masses is limited to situations in which adjacent bone involvement is suspected. MR imaging is considered, in most cases, to be the initial imaging modality of choice. The
indica-
contrast
long
is a
benign and malignant lesions. There has been little agreement about the mole of P-3i MR spectroscopy in tumor follow-up (7i-7S). Rapidly evolving and variable techniques have resulted in contradictory data. The litenatune has indicated a nonuniformity in localizing techniques, a relatively small, heterogeneous group of tumors studied, and varying sampling intervals. The evolution of such multivoxel techniques as one-dimensional chemical shift imaging has resulted in some optimism (71). Early attempts to chamactemize phospholipid membrane-related peaks (phosphomonoesters, phosphodiestems) have been successful (71-76) and show a decrease in these peaks with successful therapy. These values and measurements of inorganic phosphate and phosphocreatine signal intensities may provide clues to help predict tumor response. The mole of MR spectroscopy in this group of patients is
of
MR
imaging
to
demon-
strate the presence or prove the absence of a mass cannot be underrated. This modality offers a 100% negative predictive value in cases in which softtissue masses are suspected. MR imaging may help in diffenentiating benign from malignant masses in more than 90% of cases (SO). Benign masses are generally sharply defined, sometimes encapsulated, homogeneous, and void of penitumoral edema (59,77,78).
Malignant
demonstrate margins,
indistinct, inhomogeneous
sity,
penitumomal
and
masses
frequently
infiltrating signal edema
inten-
(59,78).
Unfortunately, theme is overlap tween these groups. In many imaging is limited to predicting
Radiolov
becases, MR domi-
a
355
Figure
a.
b.
Figure
25.
weighted at the
(a) Radiograph
image joint
line
depicts and
of a lateral
the fracture
condyle
line.
There
even
infiltrating ing
when muscle
fascial
planes.
the or
hemangioma bone
Finally,
or
is is cross-
atrophy
on
hypoplasia of surrounding musculature can be seen in pediatric soft-tissue hemangiomas. Phleboliths are not readily identified on MR images, and therefore, plain madiogmaphs are a useful supplement to the MR evaluation. 356
a
Radiology
Sagittal
gradient-echo
image
of
fracture
(Milch
is rotation
type
and
II).
(b)
Coronal
displacement
Ti-
of the fragment
metaphysis.
nant histopathologic composition mathem than histologic diagnosis, and biopsy is often needed (Fig 24). On occasion, MR imaging may be melatively specific. Certain characteristic lesions exist, including lipomas, hemangiolymphangiomas, hematomas, subcutaneous fat necrosis, and popliteal cysts. In these instances, biopsy may be obviated (77). A lipoma will typically be seen as a well-defined, circumscribed lesion of the same signal intensity as subcutaneous fat. Septations within the lesion can be prominent, but theme is usually a lack of surrounding edema. The MR appearance of pediatric muscular hemangioma has recently been reported (79). Hemangiomas most often appear heterogeneous and are typically seen as intenmediate signal intensity on Tiweighted images with increased signal intensity on T2-weighted images. A serpentine lesion appearance is typical. The presence of fat within the lesion is highly suggestive of hemangioma, since the matrix of hemangioma is eithem fat or fibrous tissueoand few pediatmic tumors contain significant amounts of fat. However, the absence of a fatty matrix does not exclude the diagnosis of hemangioma. There is a lack of edema in the surrounding soft tissues,
26.
a posttraumatic physeal bone bar. The highsignal open physis is seen anteriorly. The posterior closed physis and the anterior convex bowing deformity are appreciated.
PERIARTICULAR IN
and late
DISORDERS CHILDREN
Most applications of MR imaging in around the joints of children meto trauma: acute injuries, chronic
stress,
and
old
are unique also occur most often childhood section.
Acute
injuries.
Some
disorders
to children; other injuries in adults. The entities that induce symptoms during will be discussed in this
Fractures
Management of acute fractures depends on the presence of displacement or notation of fracture fragments and whether there is dislocation at a joint. Most fractures involving a joint are meduced and pinned if there is more than 2 mm of displacement at the joint. In young children, delineating a fracture on a plain radiograph may be difficult, since the large amount of cartilage present is not seen. Elbow fractures can be particularly complex, and arthmogmaphy
can
be
required
for
fracture
delin-
eation and characterization. If alignment is in question, ing
is our
ing
complex
preferred
method
intraamticular
MR of
imag-
evaluat-
fractures
and unstable fractures after closed meduction. Ti-weighted or gradient-echo sequences will define bone and cantilage and allow accurate assessment of both the bony and cartilaginous components of the fracture as well as the precise alignment of bone and cartilaginous fragments (Fig 25).
Figure the
27.
knee
ment
Sagittal shows
of
the of
the
bone
fluid
cartilage
and
A highline
fragment
of frag-
dissecans. synovial
rounding
image
nondisplaced
osteochondritis
signal-intensity ture
Ti-weighted
a loose,
sur-
indicates loosening
fracof
the
piece.
Physeal
Injury
One
to
involve damage plate,
two
percent
the physis to a portion with
a resultant
bar. A physeal growth at the shortening. the less
than
physis,
If a bone
there
will
left
to allow
of
bar be
the can
bone
the
amount
develop
physis bar total be
as
continues
to
accounts areas
mesected
sufficient further
that
further bone
may
open 50%
the
determine
physeal
Deformity (80).
fractures
bar prevents site and causes
remaining
grow
of
result in permanent of the growth
normal bone
for of
the
and physis
growth.
of physis
To
in-
May
1991
pair. This can make interpretation of signal within the peripheral meniscus on postthenapeutic MR evaluation unreliable (88). Deutsch et al have shown that grade III signal may persist as long as 27 months after an injury despite healing confirmed on follow-up amthroscopic examinations (88). Persistent signal intensity at the site of previous injuries
b.
Figure 28.
Bilateral discoid lateral menisci seen in coronal and (b) left knees. On the right, there is increased
(a) right coid
lateral
discoid
meniscus.
meniscus
A torn is seen
and
on
the
macerated left.
No
meniscus discrete
volved, MR mapping can be performed (81). Images should be acquired pempendiculam to the deformed physis in two planes
and
will
show
interruption
of
the low-signal-intensity physis on Tiweighted images or high-signal-intensity physis on T2-weighted and gradient-echo images. The physeal line is lost
when
a complete
bone
ban
devel-
ops (Fig 26). If the growth plate is damaged but not closed, the physeal line will be distorted but the signal intensity will remain normal. Oblique growth lines indicate asymmetric growth across the physis.
Osteochondritis
Dissecans
Osteochondnitis dissecans is considemed a traumatic lesion that occurs most often at the knee, the ankle, and the elbow. The abnormalities occur at the sites
of
impact
for
these
joints
(82-84).
Irregularity of the nonarticulating postenor aspect of the condyles should not be mistaken for osteochondral lesions (85). Treatment of osteochondral fractures varies with lesion severity. Complete displacement of the osteochondral fragment from its site of origin requires removal of the loose body. If the fragment
is not
displaced
cartilage is cracked fragment may be moved, or treated Treatment varies dral fragment is lying cartilage is will
drill
flow
and
choose Lesion should planes: images weighted Ti-weighted the bone
Volume
such
but
lesions
promote
the
overlying
on fissured, the pinned in place, meconservatively. when an osteochonin place and the overintact. Some surgeons to
increase
healing.
blood
Others
to treat them conservatively. staging with MR imaging be done by imaging in two T2-weighted or gradient-echo in at least one plane and Tiimages in the other. On the or proton-density image, defect is delineated and the
179
a
Number
2
was
tear
was
gradient-echo signal intensity found seen
images within
at surgery. at
MR
of the the dis-
The
thickened
examination.
overlying cartilage assessed. Loss of signal intensity in the articular cartilage on Ti-weighted images indicates degeneration. At arthnoscopy, the cartilage will appear intact but will be soft and spongy when probed. High-signal-intensity synovial fluid or granulation tissue detected around the bone defect on T2weighted on gradient-echo images mdicates a crack or fissure has occurred around the fragment and therefore the fragment is loose (Fig 27). At surgery, the lesion may have the appearance of a “linoleum flap.” A crack or fissure of the cartilage only without loosening of bone fragment will best be determined on T2-weighted images, since fluid cannot always be distinguished from cartilage on gradient-echo images.
Internal Deranement, and Tendon Injury
in
Meniscal
injuries
children
and
common that
Ligament, are
may
not
become
as participation
result
in
a high
uncommon even
degree
of joint
stress at an earlier age accuracy of MR imaging
increases. in the
tion
with
of
menisci
more
in activities
is 95%,
The evalua-
a false-neg-
ative mate of 4.8% (sensitivity, 95%; specificity, 91%). For the anterior cruciate ligament, the overall accuracy is 95%. T2-weighted sequences are associated with greater sensitivity, specificity, and accuracy than are Ti-weighted sequences for the evaluation of anterior cruciate ligaments; the false-negative mate approaches 0% (86,87). In children, horizontal, linear high signal intensity will be seen in the region of the chondroid matrix. This is a normal finding and does not represent degenerative change. Because
of
the
peripheral
blood
sup-
ply, a tear in the outer third of the meniscus may heal with conservative management as well as operative me-
may
account
for
some
reported
cases of disagreement between MR and arthroscopic findings. Theme is a spectrum of normal MR appearances after partial meniscectomy (89). Standard MR criteria can be used to diagnose tears in the absence of marked contour irregularity; however, the diagnosis of tears of segments with marked contour irregularity must be made cautiously, since this irregularity can mimic a tear and may not be predictive of an arthroscopically visible tear. Ligament and tendon injuries are well shown with MR imaging (90). An imaging plane parallel to a large tendon such as the patellar tendon will adequately show the integrity of the tendon. Sections perpendicular to small tendons and ligaments will more accumately reveal abnormalities in these structures. Fluid in tendon sheaths and within
the
nitis.
Fraying
fibers
tendons
is seen
Discoid
is seen
or rupture with
partial
with
tendi-
of the
tendon
teams.
Meniscus
The discoid meniscus occurs developmentally when the meniscus fails to perforate centrally, resulting in a slablike appearance instead of the normal semilunar configuration. It occurs almost exclusively in the lateral compartment and is prone to easy tearing (Fig 28a). In the young child, it may cause pain and instability and can elicit snapping on clunking on examination. Indirect signs of a discoid meniscus on radiogmaphs include a high-riding fibula,
hypoplastic
lateral
condyle,
and
widened lateral joint compartment. On MR images, asymmetric meniscal height of more than 2 mm, as well as three or more “bow ties” on S-mmthick contiguous sagittal images, has been described as diagnostic of a discoid meniscus (91). The complete slab can be seen on coronal images and is the
most
agnosis
reliable
(Fig
way
to
confirm
the
di-
28).
Legg-Calv#{233}-Perthes Avascular Necrosis
Disease!
In advanced stages of Penthes disease, MR imaging is useful for the evaluation of the thickness and shape of nonosseous structures such as the femoral and acetabulam cartilage. This modality may also provide positional evalRadiolo2vc7
Figure the
29.
hips
disease.
Coronal
in a boy There
Ti-weighted
with
image
of
Legg-Calv#{233}-Perthes
is complete
loss
of
signal
and
collapse of the left femoral epiphysis. Thickening of both the left femoral epiphyseal and the tilaginous
acetabular femoral
cartilage is seen. The head is not deformed,
and there is no loss of containment cated by the position of the labrum
car-
as indi(arrow).
b.
a. Figure clearly uation of the to determine
femomal head and loss of containment
subluxation.
These
findings
labrum and
are
same more
30.
Legg
demonstrate
Calv#{233}-Perthes
a cold
child shows subtle difficult to appreciate
disease
epipyhysis. decreased than
of the
right
femoral
(b) Ti-weighted
signal intensity the scintigraphic
epiphysis.
coronal
(a)
image
of the right abnormality.
Bone
scintigrams
of the hips
in the
femora! epiphysis, Radiographs were
which normal.
is
mdi-
rectly assessed on plain madiogmaphs but are otherwise seen only with amthrography. The decision to perform surgery
in
a child
with
advanced
Perthes disease depends on the severity of the femoral head deformity, the degree of labmal eversion, and the loss of containment with subluxation. MR abduction views of the hip will help determine reducibility, but the gantry size limits how much abduction can be achieved. The dynamics of the hip are somewhat better assessed with anthrography than with MR imaging. Most cases of Perthes disease are found at advanced stages. Seldom do we have the opportunity to make the diagnosis early. The typical MR appearance of Perthes disease is loss of signal intensity
within
the
femoral
epiphysis
on Ti-weighted images (Fig 29). The appearance may be variable, with patchy loss of signal intensity or only slight decrease in signal intensity (3). In some cases, the abnormality is subtle and the lesion, difficult to detect (Fig 30). Scintigmaphy can be more specific than MR imaging, and the moles of MR and scintigraphy for early diagnosis are not yet defined. At present they are complementary.
Arthritis Cartilage
thickness,
joint
358a_Radiology
Figure
b. 31.
sification
Proximal focal femoral deficiency of the femoral neck is seen on the
tamed through the left hip shows fracture. Marrow signal intensity and proximal surrounding
femur marrow
as a result seen on
of the magnetic gradient-echo
described as being useful in diffementiating synovial hypentrophy from joint effusion. The greatest value of MR imaging may be in evaluating response to therapy sooner than it can be detected clinically or radiographicaily.
Congenital
on the radiograph.
left
an intact cartilaginous is suppressed in the
effusion,
synovial hypertrophy, and subchondral cysts are all better evaluated with MR imaging than with any other modality (92,93). In the young child, radiographic assessment of cartilage loss is particularly difficult because of the large amount of growth cartilage present. Contrast enhancement with gadopentetate dimeglummne has been
-
a.
Disorders
Complex and late diagnostic cases of congenital dysplasia of the hip are often difficult to reduce and treat. MR imaging may be useful in evaluating and identifying the causes of failed reduction, such as a thickened ligamentum teres or an infolded labmum. Fatty
(Aitken (b) Coronal
type
femoral
neck,
ilium,
effect
of trabecular
tissue
is easily
identified
may
be a cause
tion
to complete
within
MR
does
not
require
verse
head.
spica
Other be well
cast
There on
is no MR
congenital delineated
several
surgical
me-
has been apit may be
reduction. or
Trans-
gradient-echo
aging can be performed tion to document position ral
a hip.
after
cast hip,
to confirm Ti-weighted
and
obstrucof
“melt”
of
acetabulum imaging
reduction
will
section. After a spica plied for an unstable necessary
bone
the
at
osobhead, on
femoral
of temporary
tissue and
Incomplete image
no evidence
ossified
pulvmnar
weeks
with
ischium,
susceptibility images.
Pulvinar
A). (a) gradient-echo
artifact
imaging
im-
without of the
sedafemo-
from
a
(94).
disorders with MR
may also imaging.
May
1991
In some forms of proximal focal femoma! deficiency, there may be a cartilaginous femonal neck that is delayed in ossifying. The cartilage is clearly defined with MR imaging when images are angled parallel to the femomal neck (Fig
14.
31).
15.
Parker et a! have described identification with MR imaging of the anterior tibia! tendon hypoplasia in clubfoot defommity (95). We have shown increased tibial cartilage thickness after external fixator distraction in a child with chondroectodemmal dysplasia. Evaluation of Madelung deformity and Blount disease for physeal injury and growth amrest has not shown a primary physeal abnormality. MR imaging will continue to play a dominant mole in the diagnosis and pretherapeutic, postthemapeutic, and follow-up evaluation of pediatric musculoskeletal disease. Further experience with this modality will likely bring additional applications of MR imaging for the evaluation of pediatric musculoskeletal disorders. U
with
advancing
ative 1932; Kricun sion: italy
response to stimuli. J Lab Clin Med 17:960-962. ME. Red-yellow marrow converits effect on the location of some so!bone lesions. Skeletal Radio! 1985;
1.
16.
H,
imaging
Dietrich
RB,
of bone
marrow
Assist SC,
Tomogr
Sebag
children.
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May
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