Musculoskeletal Mark Karen

D. Murphey, M. Simpson,

MD MD

Louis H. Wetzel, MD #{149}John Herbert B. Lindsley, MD

MR

Magnetic resonance (MR) imaging was performed in seven asymptomatic volunteers and i7 patients with clinical and radiologic evidence of sacroiliitis. MR imaging findings were compared with those at computed tomography (CT) to determine the MR imaging appearance of the sacroiliac joint when normal and in sacroiliitis. The normal articulation was well depicted with MR imaging. Findings of sacroiliitis were identifled in 20 sacroiliac joints (12 patients). MR imaging findings characteristic of sacroiiitis included abnormal cartilage signal intensity (95% ofjoints) and erosions (75% of joints) on Ti-weighted images. Areas of increased intensity in the articulation (80% ofjoints) or in erosions (60% ofjoints) were seen on T2weighted images. MR imaging was superior to CT for evaluation of cartilage and detection of erosions. Four sacroiliac joints (20%) and two patients (i7%) with MR imaging findings of sacroiliitis were negative at CT. The authors conclude that MR is a valuable

tecting

sacroillitis,

results

of other

method

for

de-

particularly when imaging techniques

are inconclusive. Index

terms:

studies, 337.9i

Arthritis,

337.1214

337.70

Joints,

#{149}

Joints, MR 337.70,

#{149}

sacroiliac,

MD

Errol

Levine,

#{149}

Imaging

S

Findings’

is a component of the spondyloarthropathies, which include ankylosing spondylitis, psoriatic arthritis, and Reiter syndrome (1). Involvement of the sacroiliac joint can also be seen in gout, rheumatoid arthntis, enteropathic arthropathy, and pyogenic arthritis (particularly in abusers of intravenous drugs). Clinical diagnosis of early sacroiiitis is often difficult. The symptoms of sacroiliitis

ACROILIITIS

may

be indistinguishable

from

those of mechanical causes of low back pain (2). Also, physical findings are frequently obscured by the overlying soft tissues. Consequently, radiologic evaluation plays a major role in the diagnosis of sacroiliitis. Several imaging techniques have been used to examine the sacroiliac joint. These include conventional radiography and tomography, scintigraphy, and computed tomography (CT) (3-6). Recently, magnetic resonance (MR) imaging has been used extensively to evaluate intraarticular abnormalities (7,8). However, MR imaging of the sacroiliac joint has received little attention (9). The purpose of our investigation was to determine the MR imaging appearance of the normal sacroiliac joint and to identify MR imaging findings of sacroiiitis. Comparison with CT examinations or conventiona! tomography (one patient) was performed in all patients.

sacroilhitis

was

1991;

Between 14 sacroiliac volunteers with known evaluated

From the Departments

ogy (M.D.M., L.H.W.,J.M.B., (K.M.S., H.B.L.), University

Center, KS 66103.

Rainbow From

Blvd at the

1988

bly. Received December quested January 24, 1991; March 14; accepted requests to M.D.M. C RSNA, i99i

March

of Diagnostic

Radiol-

EL.) and Medicine of Kansas Medical 39th St. Kansas City, RSNA scientific assem17, 1990; revision rerevision received 21. Address reprint

January

i988 and April

prospectively

All patients matology

1990,

joints of seven asymptomatic and 34 joints of i7 patients or suspected sacroiiitis were

were service

with

referred and

from

fulfilled

MR

imaging.

the rheuat least

two

of the following criteria: (a) clinical evidence of sacroihitis including low back pain and focal sacroiliac tenderness, (b) underlying roiliitis

dence tional

disease

associated

with sac(spondyloarthropathy), or (c) evisuggesting sacroiliitis on convenradiographs. The final diagnosis of

patients

surgical, or of the diag-

!nformed consent was obtained from all patients, and approval for the project was obtained from the Human Subjects Committee. The asymptomatic volunteers consisted

of four

19-42

years

men old

and

three

(mean,

women,

30 years).

Patients

with suspected sacroiliitis consisted of nine men and eight women, 18-70 years old (mean, 37 years). Causes of sacroiliitis included ankylosing spondylitis (n = 5), Reiter syndrome (n = 4), psonatic arthritis (n

6), and

=

study

septic

included

varying

arthritis

patients

(n with

= 2). The sacroiliitis

of

severity.

All patients underwent anteroposterior pelvis radiography, 16 underwent CT, and

one underwent

conventional

of the

joints.

ing

sacroiliac

studies

2-week

were

tomography

CT and

performed

interval.

MR imag-

within

Multisection

a

spin-echo

MR imaging was performed with a superconducting imager (Magnetom; Siemens Medical Systems, !selin, NJ) operated at 1.0 T and

view,

an elliptical

30 cm). Images

coronal

long

axis

prescribing

surface

coil (field

were

of the

an oblique

obtained

sacroiliac

plane

of

in the joint

from

by

short

acquisition sagittal “scout views.” For Tiweighted images (600/25 [repetition time msec/echo time msecj), eight acquisitions were averaged and obtained with use of a 256 x 256 matrix. For T2-weighted images

pulse

METHODS

AND

to those

fectious sacroiiitis, histologic, bacterial culture confirmation nosis was obtained.

four

acquisitions

and a 256 x i28

180:239-244

MATERIALS

1

restricted

who, by consensus, had clinical and radiologic evidence of inflammation in the sacroiliac joints. in the two patients with in-

(2,100/90), Radiology

PhD

MD,

#{149}

Sacroiliitis:

imaging

M. Bramble,

#{149}

Radiology

sequences,

were

was

matrix 4-mm

averaged

used.

For all

sections

were

sep-

arated by 1-mm gaps. Patients were exammed supine with their knees flexed for comfort.

The

MR

imaging

time

per

approximately

weighted weighted

sequence, 20 minutes; T2sequence, 18 i rtinutes). CT was with GE 9800 (GE Medical Sys-

performed

tems, mens)

Milwaukee) scanners.

45 minutes

study

averaged

or Somaton The standard

of Carrera

et al and Lawson

used

the gantry

with

(TI-

DR (Sietechnique

et al (4,6) was

angled

to be as par-

allel as possible to the long axis of the upper sacrum. The only exception was case 17, in which

conventional

axial

CT

tomograms

was

performed.

were

The

obtained 239

a.

b.

Figure

Figure

1.

Coronal

MR image

(600/25)

of hg-

amentous part of normal sacroiliac joint in a 42-year-old female volunteer shows high signal intensity representing adipose tissue (solid arrows). Areas of low signal intensity represent loose connective tissue and interosseous sacroiliac ligaments (arrowheads).

There

is a small

“insertion

pit” (open

use

of a Polytome

cal

Systems,

Shelton,

medium

screens

(Eastman

(Philips

Conn),

with

Kodak,

Dihlmann’s

Medi-

Kodak

Kodak

Lanex

TMG

Rochester,

film

NY),

and

(3) technique.

MR images hyzed aging

unit

of the volunteers

were

first to establish the normal appearance of the sacroiliac

Three radiologists reviewed all MR

the CT studies

ana-

MR imjoint.

(M.D.M., L.H.W., images separately

in the

17 patients

J.M.B.) from

with

sus-

pected sacroiliitis for the following findings: (a) abnormal cartilage signal intensity, (b) presence or absence of erosions, (c) appearance of juxtaarticular bone marrow, and ( d) sacroiliac joint space appear-

ance. Results ered abnormal the following mal uniform

of MR imaging were consid(sacroihiitis) if any one of was present: (a) loss of norcartilage signal intensity, (b) Ti-weighted images, or (c)

erosions increased

on signal

erosions

on

mal

intensity

CT findings

dral sclerosis, intraarticuhar

included

CT findings

dicative

of sacroihiitis;

these

changes

was

listed

as equivocal.

pared

with

CT

MR scans

ankylosis,

chondral

sclerosis),

erosions,

and

each

joint

pendently

evaluated,

was superior mality. There cases. In 25%

showed gories,

and

the

a consensus

evaluation. reviewers

which

in two

contradictory

was

For inde-

modality

or fewer

cate-

responses,

used.

RESULTS MR Imaging:

Normal

and

cortices

(arrowheads).

guished increased

and that low signal intensity signal intensity are noted.

(b) Coronal

Note

MR image

(2,100/90) is present

sharp

sacroiliac

joint

in a 32-year-old

fe-

thin zone between

of intermediate signal intenadjacent low-signal-inten-

definition

of adjacent

shows

that

within

the

seven volunteers. The ligamentous portion of the joint is posterior and obliquely oriented and contains adipose tissue with focal areas of low

mography.

signal

four

intensity,

marrow

the cartilage

sacroiliac

cannot

joint

margins

be distin-

(arrows);

no areas

of

representing

loose

MR imaging clearly distinguished the synovial and ligamentous cornpartments of the sacroiliac joint in all

All of these plus four addiarticulations totaling 20 joints

tional

(12 patients) had tive of sacroiliitis

patients

2; Reiter

ties and marrow defects (insertion pits) at the attachment of these ligaments. The synovial compartment of

Table

the sacroiliac joint is anterior and more vertically oriented, corresponding to the inferior one-half to twothirds on plain radiographs. MR irnaging allowed direct identification of the cartilage in the synovial cornpartment as a thin zone of intermediate signal intensity on Ti-weighted images in all 14 articulations of the volunteers (Fig 2a). In 12 of the 14 normal sacroiliac joints (86%), the sacral

osteoarthntis cally suspected

mm).

The

were

identified

iliac

and

sacral

as areas

on

either

side

cortices

of low of the

signal carti-

lage. The bone marrow on both sides of the sacroiliac joint was sharply defined, without marginal irregularity. Ti-weighted images were best for depicting anatomic detail. On T2weighted images, the cartilage was not

consistently

distinguished,

which case low signal observed (Fig 2b).

in

intensity

Abnormal

clinical

ing

Sacroiliac

were

patients,

considered or, in one

16 (10

to have patient,

patients)

sacroiliitis at conventional

CT

with

15; and

the basis

of the

findings,

three

as having

clinical

and

MR imagsacroiliac initial cliniTwo

suggesting normal

CT and MR imaging In 19 of 20 joints

examination. (95%) with

iliitis,

images

novial

pa-

conventional

findings considered

Ti-weighted

and in

patients

and not the sacroiliitis.

radiographic roiliitis were

sep-

17), sacroilii-

(Fig 3). Clinical are summarized

diagnosed

tients

compartment

sacafter

sacro-

in the

showed

sy-

loss

of

the normal, thin zone of intermediate signal intensity representing cartilage (Fig 3). This was replaced by areas of inhomogeneous tissue with mixed signal intensity. Cartilage loss was not complete throughout each involved sacroiliac intensity

Focal

joint. similar

areas

to that

of signal

of cartilage

remained in 18 of the (90%) with sacroiliitis.

20 articulations Eleven of these

sacroiliac creased

showed inin areas of

joints signal

thickening one patient loss

was

(61%) intensity

on T2-weighted (case 12), such the

only

MR

images. cartilage

imaging

In

finding,

and the normal.

corresponding CT study was In 16 (10 patients) of the 20 articulations (80%), there were focal or linear areas within the synovial

the in our

16 and

1. On and

In case

compartment that showed abnormal high signal intensity on T2-weighted images (Fig 4). Both cases of infectious sacroiliitis showed increased signal intensity on T2-weighted images in

was

Joint 34 articulations

case

cases

unilateral findings

indica-

arthritis,

syndrome,

tic arthritis, tis was imaging

abnormalities at MR imaging.

(psoriatic

connective tissue and the interosseous sacroiliac ligaments (Fig 1). Seven normal sacroiliac joints (50%) showed prominent sacral irregulari-

Of the

#{149} Radiology

sacral

arrows).

MR Imaging: Sacroiliac

Joint

240

iliac

(curved

intensity

for each category of abnorwas unanimity in 75% of of cases, one respondent

a difference without

production abnormalities,

joint

determined

toor sub-

cartilage

overall

was

were

osteophytes,

sity

of normal

(a) Coronal MR image (600/25) shows cartilage (straight arrows) sandwiched

somewhat thinner anteriorly and inferiorly (mean, 2.4 mm; range, 2-3

in-

or conventional

of bone

volunteer. sity representing

compartment

com-

or two

one

the study images

male

of synovial

of

subchonerosions, Any

only

images

and iliac components of the cartilage were focally separated by an intervening linear zone of low signal intensity. The cartilage had a maximum thickness of 4-5 mm posteriorly (mean, 3.1 mm; range, 2-5 mm), being

considered

when

seen,

or

Abnor-

sacral

were

for findings

(osseous

joint

images.

joint space loss, osseous ankylosis.

of these

mograms

in the

T2-weighted

MR

arrow)

in the left sacrum.

with

2.

17

soft

rounding

were

at CT to-

tissues the

and sacroiliac

the

marrow joint.

surThe

adi-

pose tissue of the ligamentous compartment was involved by the inflammatory process in only four July

1991

Table

i of

Summary

Imaging

Findings

in Patients

with

Suspected

Sacroillitis MR Findings

Cause of Sacroiliitis

Case NoJ Age (y)/

Abnormal Cartilage Signal Intensity

Conventional

CT

T2 Abnormality

Gender

Radiographs

(R/L)

(R/L)

(RJL)

(R/L)

Erosions

Consensus Diagnosis

Psoriatic arthritis 1/47/F

+

+1+

+1+

+1+

+1+

2/47/F

+ + + +

+1± +1+ +1+

+1+1+ +1+

+1+1+ +1+

+1+1+ +1+

Sacroihitis Unilateral Sacroiliitis Sacroiliitis

+1+ ±1±

+1+

-I-

-I-

Sacroiliitis

-I-

-I-

-I-

Osteoarthritis

+1+

+1+

+1+

+1+

+1+

-I-

-I-

-I-

Sacroiiitis Sacroiliitis Normal

1Q’2a’M

+/+ +1+ -I+1-

+1+

+ ± +

+1+

+1+

+1+

11/42/F

±

±1±;

-I-

-I-

-I-

Sacroilhitis Osteoarthritis

i2,’lWF ia’45i’M i4/19/M 15/28/M

±

-I-I--I-I-

+1+ -I-I-I-

-I-I-I-1+

-I-I-I-1+

Sacroiiitis Osteoarthritis Normal Unilateral

sacroihiitis

16/43/F

+ +

+1-

+1-

+1-

+1-

-1+

-1+

-1+

-1+

Infectious Infectious

sacroiliitis sacroihiitis

3/31/F 4/571M 5/Sl/M 6/70/M

±

sacroilhitis

Ankylosing spondyhitis 7t2&fl 8/40/M 9120,’M

-I-

Reiter syndrome

Septic

± ± ±

arthritis 17/40/F

Note.-R/L * Conventional

Figure lateral

=

tight/left, + tomography.

=

presence

of abnormality,

3. Coronal MR image (600/25) of unisacroiliitis associated with psoriatic

arthritis in a 47-year-old woman. There is loss of cartilage in right sacroiliac joint with replacement by inhomogeneous mixed-signal-intensity tissue (large straight arrow) and widening of right sacroiliac joint. Cortex has areas of increased signal intensity (small straight arrows), and the marrow margin adjacent to right sacroiliac joint is irregular, representing erosions (open arrows). Contralat-

-

of abnormality,

absence

=

4.

MR images

of psoriatic

of sacroiliac (six

heads).

increased sions (Fig

cortex

as well

as deeper

defects. Erosions were most prominent on the iliac side of the joint, anteriorly and inferiorly, and caused the Volume

180

#{149} Number

1

findings.

sacroiliitis

in a 31-year-old woman. (a) Coronal MR image (600/25) shows cartilage replacement bilaterally. Adjacent irregularity of marrow margin and increased intensity in cortex representing erosions (large straight arrows) result in sacroiliac joint space widening. Deeper erosion (small straight arrow) is noted on heft, as is hypenntense reactive bone marrow (curved arrows). (b) Coronal MR image (2,iOO/90) shows both focal (solid arrows) and linear (arrowhead) increased signal intensity in sacroiliac joints and in most inferior erosion on heft (open arrow).

ing.

to the

equivocal

b.

Figure

appearance

cent

=

a.

eral joint shows normal cartilage (curved arrow), cortex, and marrow margin (arrow-

joints (cases 16 and 17, infectious sacroiliitis; and case 5, psoriatic arthritis with bilateral osseous ankylosis). Erosions were demonstrated in 15 (nine patients) of the 20 articulations with sacroillitis (75%) as areas of increased signal intensity in the normally low-signal-intensity sacral and iliac cortices on Ti-weighted images (Fig 4a). Erosions also resulted in irregularity of the marrow margin adja-

±

In nine

(60%),

joint

patients)

T2-weighted

widen-

row

images

signal intensity 4b). Erosions

showed

intensity

was

sequences,

within erowere associ-

ated with cartilage loss, with ception. In this patient (case

signal

articulation

articulations

one ex15, Reiter

dral ing

with

corresponding

sclerosis can

adjacent

seen

accentuates

to subchon-

on CT scans.

be subtle the

on

to the

all pulse

MR

appearance

This

find-

images

and

of joint

present with adjacent slightly thickened cartilage signal intensity (Fig 5). The corresponding CT scan was con-

In three patients (cases 6, 13), CT scans demonstrated osteophytes, subchondral sclerosis, and areas of ill-defined subchondral bone; however, corresponding MR

sidered normal. The marrow to erosions showed increased

images showed sity and absence

syndrome),

a solitary

intensity

with

i4 of the

15 joints

erosion

all pulse (93%).

was

adjacent signal

sequences This

in in-

volved a minority of erosions within each joint and was seldom a prominent finding. In 21 of the 34 sacroiliac joints suspected sacroiliitis, decreased

with mar-

widening. ii, and

cartilage signal intenof erosions. By corn-

paring results of the two imaging modalities, these three patients were judged to have osteoarthritis (Fig 6). Extensive osseous ankylosis in one patient with psoriatic arthritis (case 4) showed marrow signal intensity bridging

both

compartments

of the

Radiology

241

#{149}

a.

sacroiliac patients

joint (cases

possible

focal

areas

MR imaging crossing case, the

these tissue

between on

repetition lack

marrow

and the

in one cartilage,

bone,

became with long findings sug-

images

times.

These

of true

osseous

Comparison

fusion.

to show

regions, replacing

hyperintense gest

of osseous

failed

interposed

tional tomography and CT have the advantage of improved delineation of the complex anatomy of the sacroiliac joint (10,11). CT is considered the method of choice due to its availability, ease of examination technically, lesser interobserver variation in interpretation, and decreased radiation

at MR imaging. In two 3 and 8), CT revealed

exposure

tional

ankylosis.

of CT and

MR

imaging

lidity

compared of some

results for findings of bone production (osseous ankylosis, osteophytes,

considered

and

these

subchondral

abnormality, joint evaluation

Table were

sclerosis), erosions, are

itis

cartilage

MR imaging were and

ulations. was

in all patients.

conspicuity

improved

at MR

of affected joints. proved detection

Ero-

imaging

gle patient (case 17)

with infectious (Fig 7). Overall

tion

was

superior

59%

of sacroiliac

equivalent

in 81%

MR imaging

joints

with

imin a sin-

while

both

being

modalities

in

of early

sacroili-

DISCUSSION itis

assessment

is often

difficult,

and

the

diagnosis

on radiologic evaluation. Plain radiography remains the most widely accepted and available initial screening method. There is significant interand intraobserver variation in interpretation of plain radiographs (10). In one series, frequently

20%

depends

of plain

radiographic

(predominantly incorrect results

when (2). This

other

techniques

tional with

tomography suspected

242

#{149} Radiology

and sacroiliitis.

were

convenCT

in patients Conven-

individuals

of

in

and

in paC.

Figure 5. with Reiter

cartilage in the synovial as a thin zone of inter-

sharply

margin.

defined

that

hyaline

marrow

The

demonstrate

surface

the

sacral

to be covered

cartilage

(up

ar-

with

to 4 mm

thick),

while on the iliac side thinner fibrocartilage (up to 2 mm thick) is present (i,i3). It is likely that there is volume averaging of cartilage signal intensity, although sacral and iliac cartilages were distinguished focally in 86% of articulations. MR imaging directly enables distinction of the two cornpartments of the sacroiliac joint, with the ligamentous segment containing adipose tissue and only the synovial compartment demonstrating cartilage signal intensity. This is unlike CT, in which

the

compartments

fled only by their sition (4). The

with CT to the use of

including

can be identified

with an adjacortex and a

readings

false-negative) compared has led

as several

mediate signal intensity cent low-signal-intensity

ticular in

41%.

Clinical

findings

mens

sacroiliitis joint evalua-

with

of sacroili-

questioned,

appearance suggests hyaline cartilage (maximum thickness, 5 mm). This correlates well with pathologic speci-

of erosions

CT provided of erosions

the vapreviously

to be indicative been

strate the compartment

equally shown on CT MR images in 12% of artic-

The

findings

tients with osteoarthritis (12). The normal sacroiliac joint is well depicted with MR imaging. Tiweighted images directly demon-

in

71% of joints and equally well with both modalities in 29% . Cartilage abnormalities were best demonstrated sions scans

conven-

Recently, CT

asymptomatic

and overall summarized

2. Changes in bone production best demonstrated with CT in

with

has

with

tomography.

most

are

orientation

and

of involved replaced

remainder

of heft joint

po-

finding

of

images.

This

occurred

articulations, with by areas of inhomo-

show

normal

marrow

margin, cortex (open arrows), and cartilage (arrows). (b) Coronal MR image (2,100/90) shows increased signal intensity in erosion, suggesting edema and inflammation (arrow). No other areas of high signal intensity are seen, and the cartilage cannot be defined. (c) Corresponding coronal CT scan shows equivocal cortical irregularity (arrowhead) in

area of erosion. plane

Differences

of imaging

the sacral

can

in the coronal

be seen

appearance

by comparing

in a.

geneous mixed-signal-intensity We assume these correspond of cartilage destruction is seen pathologically

loarthropathies lage appeared sent

an

earlier

presence

stage

This

as expected No analogous

as

where cartimay repre-

of synovial

is supported

of linear

by the

increased

images for

tissue. to areas

by pannus, in the spondy-

(1). Areas thickened

on T2-weighted

characteristic

Ti-weighted

in 95% cartilage

Images of sacroiliitis associated syndrome in a 28-year-old man. (a) Coronal MR image (600/25) reveals solitary erosion on iliac side of left sacroiliac joint (arrowhead). Cartilage (straight solid arrows) is intact although slightly thickened adjacent to erosion. Right sacroiliac joint and

proliferation.

identi-

sacroiliitis at MR imaging was loss of the normal thin band of intermediate signal intensity representing cartilage on

b.

intensity

in these

inflammatory finding was

areas,

tissue. seen with

other imaging modalities, because with those techniques cartilage cannot be directly imaged. MR imaging was

superior

sessment

to CT of the

in all cases

cartilage.

The

in as-

cause July

of 1991

a.

b.

Figure 7. (2,iOO/90) intraarticular

Images reveals

of infectious sacroiliitis extensive paraarticuhar

in a 40-year-old woman. marrow and soft-tissue

(a) Coronal edema (solid

MR image arrows) and

inflammation with fluid (open arrows), which were confirmed surgically. (b ) Axial CT scan more clearly demonstrates erosions of both sacral and iliac surfaces (arrowheads) with widened sacroiliac joint and adjacent soft-tissue inflammation and fluid collection (arrow). Figure 6. Images of osteoarthritis of the sacroiliac joints in a 42-year-old woman with suspected ankylosing spondylitis. (a) Coro-

nal CT scan drah

shows

sclerosis

chondral present

iliac and

(straight

areas (curved

sacral

arrows).

of lower arrows),

subchon-

Several

attenuation suggesting

sub-

are erosions

or subchondral (600/25) shows

area

cysts. (b) Coronal MR image iliac subchondral sclerosis as of how signal intensity (straight solid

arrows);

sharp

(curved arrows)

arrows) confirm

cortical-medullary

junction

and intact cartilage (open the absence of inflammatory

changes.

ing in a true coronal plane may also have been a factor. In one case (infectious sacroiliitis), erosions were demonstrated better with CT than with MR imaging because diffuse marrow edema with decreased signal intensity on Ti-weighted images obscured the focal erosions. Higher signal intensity in bone marrow, seen with all pulse sequences adjacent to a minority of erosions,

the sacroiliitis distinguished

lateral in the to the throsis was

generally with MR

cannot imaging.

be Uni-

disease with prominent edema soft tissue and marrow adjacent sacroiliac joint suggests pyarand osteomyelitis (14,15). This seen

in our

patients

tious sacroiliitis. Increased signal sacral

and

iliac

with

intensity

cortices

with

infec-

in the adjacent

marginal irregularity and deeper defects in the juxtaposed marrow represented erosions on Ti-weighted MR images. These were seen in 75% of involved articulations and caused widening of the sacroiliac joint. Erosions were more prominent anteroinferiorly and on the iliac side of the synovial compartment, where cartilage is normally thinner and subchondral bone less protected. Erosions were associated with cartilage loss in all but

one

instance,

in which

a soli-

tary erosion had adjacent, slightly thickened cartilage. This may have been due to buds of granulation tissue from beneath the articular cartilage, as has been described in seronegative spondyloarthropathies. This can occur with or without other inflammatory synovial changes (i6). There was improved conspicuity of erosions in 8i% of articulations at MR imaging. We believe this was due largely to the superior contrast resolulion

Volume

of MR 180

imaging, #{149} Number

although 1

imag-

suggested

focal

reactive

at-

rophy with increased marrow fat. This is similar to findings noted in the lumbar spine adjacent to chronic degenerative disk disease (17) and may relate to chronic erosions. Areas of increased signal intensity on T2-weighted images were seen in the synovial compartment of the sacroiliac joint (80%) and in erosions (60%). This suggests a more edematous acute inflammatory tissue, with intraarticular fluid corresponding to linear components. The increased signal intensity on T2-weighted images is less than that expected for a purely inflammatory process. Fibrous proliferation within pannus, seen patholog-

ically

in the

may lower CT was

spondyloarthropathies, the signal intensity (3,8). superior to MR imaging in

detection of subchondral sclerosis and osteophytes. However, CT identification of subchondral sclerosis or illdefined subarticular bone may be misinterpreted

as sacroiliitis.

changes patients

have with

asymptomatic

imaging tory by

focal there sity

described and

individuals

permitted

tween

These

also been osteoarthritis

changes showing

(12,18).

distinction

degenerative

and

in three that

no

in in MR

be-

of our

patients loss

or

erosions were present and that was no increased signal intenon

T2-weighted

patients were teoarthritis.

classified

images.

These

as having

os-

ankylosis

is a sign

sacroiliitis long-standing

of (1,13). bone

At

ankylosis may demonstrate marrow signal intensity crossing the sacroiliac joint, without the presence of normal cartilage

or inflammatory

tissue.

MR

imaging disproved the presence focal areas of osseous ankylosis suggested by CT in two patients, sibly as a result of an improved nal

imaging

of as poscoro-

plane.

Several advantages of the sacroiliac joint These include direct

of MR imaging are apparent. visualization of

cartilage abnormalities trast resolution, allowing

and

high detection

conof

edema in the sacroiliac joint, erosions, and adjacent marrow and soft tissues. The coronal plane has been established as optimal for evaluation of the synovial compartment of the sacroiliac joint because of its vertical orientation

(6). CT may

obtaining

a direct

ing

by

plane

scanner MR

be restricted

true

sacral

type

on

from

coronal

orientation

(allowable

imaging,

unrestricted nal imaging These factors the fact that

the

and

gantry other

imag-

hand,

tilt). is

in performing true coroof the sacroiliac joint. may be responsible for two of our patients with

MR imaging findings of sacroiliitis (17%) and four sacroiliac joints (20%) would have been considered negative by CT criteria (Table 1). MR imaging

showed cases

inflamma-

cartilage

Osseous postinflammatory MR imaging,

changes where

CT

mal. MR imaging tection of erosions. ing was considered evaluation of the 59%

of articulations

of sacroiliitis findings

in all

were

abnor-

also improved deOverall, MR imagsuperior to CT in sacroiliac joint in (Table

2). Lack

of

ionizing radiation (15-20 mGy per CT examination) is also a distinct advantage, since many patients with sacroiliitis are young and of reproductive age (4). MR imaging may have a parRadiology

#{149} 243

ticular application in adolescents, in whom the normal sacroiliac joint often simulates sacroiliitis on radiographs (10). CT has not been as extensively investigated in adolescents, and scintigraphy overlap

is less

helpful

of normal

and

with

the

abnormal

sac-

roiliac joint advantages

ratios in this age (i9). Disof MR imaging include

cost,

of imaging

length

time

required,

imager availability, and some limitations on imaging patients with claustrophobia, ferromagnetic surgical clips, or cardiac pacemakers. Limitations the relatively

of this study small number

tis, we necessarily with

varying

included

stages

of disease

patients and

compared findings with other imaging techniques. CT remains an excellent and proved method to evaluate sacroiliitis. Further studies in more closely defined populations with early sacroiliitis are necessary to provide on the sensitivity and specificity of MR imaging relative to CT in diagnosing sacroiliitis. In conclusion, although sacroiiitis is frequently apparent from plain radiographs, uncertainty remains after initial imaging in a significant number of patients. MR imaging is a valuable joint.

for evaluating Furthermore,

discovered

while

the sacroiliitis

performing

may

be

changes

difficult cases conventional

a unique

early

ability

in sac8.

secondary ized with

before

9.

in

10.

cartilage

the

occurrence

script

expertise

and Fern Winter

i.

15.

D, Niwayama C. Diagnosis of disorders. 2nd ed. Philadelphia: Saunders, i988; 695-6%, 932-953. Ryan L, Carrera C, Lightfoot RW, Hoffman RG, Kozin F. The radiographic diagnosis of sacroiliitis: a comparison of different views with computed tomograms of the

Resnick

bone and joint 2.

sacroiliac 3.

4.

5.

6.

joint. Arthritis

Rheum

1985; 8:1028-i034. Klein MA, Winalski CS, Wax MR, PiwnicaWorms DR. MR imaging of septic sacroiliitis. J Comput Assist Tomogr 199i; i5:i26132.

16.

Pasion

17.

ing spondylitis: histopathohogical Ann Rheum Dis 1975; 34:92-97. Modic MT, Steinberg PM, RossJS,

EC, Coodfellow

TJ, Carter

1983; 26:

760-763. Dihlmann W. Diagnostic radiology of the sacroiliac joints. Chicago: Year Book Medical, 1980; 1-26. Carrera GF, Foley WD, Kozin F, Ryan L, Lawson TL. CT of sacroihiitis. AJR 198i; 136:41-46. De Smet An, GardnerJD, Lindshey HB, Coin JE, Fritz SL. Tomography for evaluation of sacroihiitis. AJR 1982; 139:577-581. Lawson IL, Foley WD, Carrera CF. Berhand LL. The sacroiliac joints: anatomic, plain roentgenographic, and computed tomographic analysis. J Comput Assist Tomogr

diag-

14.

for manu-

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Acknowledgments: The authors thank Rick Lintner, RST, and Doris Carr, RST, for their

technical

and wrist. II. Pathohogic correlations and clinical relevance. Radiology 1986; 160:147152. Beltran J, CaudillJL, Herman LA, et al. Rheumatoid arthritis: MR imaging manifestations. Radiology 1987; 165:153-157. Hoffman A, Theissen P, Zeidler H, et aL Magnetic resonance imaging of sacroiliitis (abstr). Arthritis Rheum 1989; 32(suppl): 112. Forrester DM, Hollingsworth PN, Dawkins nosis of sacroiliitis. Chin Rheum Dis 1983; 9:323-332. De Somer F, De QuekerJ, Baert AL. Comparison of computed and conventional tomogranis in the evaluation of sacroiliitis. JBR-BTR 1985; 68:351-354. Vogler JB, Brown WH, Helms CA, Cenant HK. The normal sacroiliac joint: a CT study of asymptomatic patients. Radiology i984; 151:433-437. Sashin D. A critical analysis of the anat-

and noninvadetection of

osseous changes other modalities.

Weill KL, BeltranJ, Lubbers LM. Highfield MR surface-coil imaging of the hand

RL.

in conjuncmethods and

to image

directly may allow

synovitis

of

sacroiliac MR im-

7.

back

use of MR to be familiar

T2-weighted images, areas of increased signal intensity may be present. MR imaging can be helpful

information

method

of low

findings for identification of sacroiliitis on Tiweighted images are loss of the thin zone of cartilage and erosions. On

abnormalities sively. This

MR imsacroilii-

causes

with the MR imaging roihitis. MR imaging

has

include of pa-

To characterize resulting from

for other

pain. With the increased imaging, it is important

clarifying tion with

tients examined and the absence of histologic confirmation, except in two patients with infectious sacroiliitis. Investigation of larger groups of patients will be necessary to corroborate our findings. aging changes

aging

18.

19.

JR.

JW.

Degenerative

Pre-ankyhosreport. Masaryk

disk disease:

assessment of changes in vertebral body marrow with MR imaging. Radiology 1988; 166:193-199. Resnick D, Niwayama C, Coergen TC. Degenerative disease of the sacroiliac joint. Invest Radiol 1975; 10:608-621. Miron SD, Khan MA, Wiesen EJ, Kushner I,

Bellon

EM.

The vahue of quantitative sacin detection of sacroilii-

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244

Radiology

#{149}

July

199i