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From

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s of the AFIP

Archive This article meets the crzteriafor 1.0 credit hour in Category I of theAMA Physician ‘s RecognitionAward. To obtain credit, see the questionnaire at the end ofthe article.

Typical,

Atypical,

Features

are

Meningiomas

system

Peter MD

with

C. Buetow,

#{149}

CPT,

USA

MC,

the most common nonglial primary tumors and the most common extraaxial neoplasms,

15% ofall characteristic

approximately

plasms,

Misleading

in Meningioma

MicbaelP. Buetow, MD James G. Smirniotopoulos,

nervous

and

are several important ically typical meningioma

intracranial pathologic

histologic can

tumors. They and imaging

of the central accounting for

are usually benign features. However,

variants of meningioma, have unusual or misleading

and even radiologic

neothere a histologfeatures

that may not be suggestive of meningioma. The typical meningioma is a homogeneous, hemispheric, markedly enhancing extraaxial mass located over the cerebral convexity, in the parasagittal region, or arising from the sphenoid wing. Meningiomas may originate in unexpected locations such as the orbit, paranasal sinus, or ventricles or be entirely intraosseous (within the calvaria). Unusual imaging features such as large meningeal cysts, ring enhancement, and various metaplastic changes (including fatty transformation) can be particularly misleading. Because meningiomas are so common, the radiologist must be aware of their less frequent and uncharacteristic imaging features in order to suggest the correct diagnosis in cases that are atypical. INTRODUCTION Meningiomas represent incidental (asymptomatic)

U

approximately intracranial

15% of all symptomatic and neoplasms (1,2). Symptomatic

about 33% of all meningiomas

occur two to three times more commonly in female patients, especially those in the middle age (40-60 years) group, and generally are benign neoplasms that are denived from meningothelial cells (1,3). Meningiomas typically occur as extraaxial lesions attached to the dura mater and exhibit “cortical buckling” of the underlying

Index

terms:

Hemangiopericytoma,

neoplasms,

10.34,

RadloGraphics I

From

1991;

the

and

Fern

shey ton,

Medical Center, DC (P.C.B.); and Bethesda,

accepted

September

The opinions or as reflecting

CRSNA,

Pathology

DC 20306-6000;

0.G.S.), the

CT,

Armed

Department

10.1211

Md

(P.C.B.,

5. Address

J.G.S.). reprint

Receivedjune requests

contained herein of the Department

Forces

of Radiology,

Hershey, Pa (M.P.B.); the Department the Department ofRadiology and

or assertions the views

Health

#{149} Meninges,

#{149} Meninges,

MR studies,

10.1214

#{149} Meninges,

106

of Radiologic

Washington,

Sciences,

sity of the

11:1087-1

Department Sts,

13.3149

10.366

of Radiology, Nuclear Medicine, 7, 1991;

revision

Institute

of Pathology,

Pennsylvania Walter Reed Uniformed requested

Bldg

State

54,

University,

Rm M121, Milton

Alaska S. Her.

Army Medical Center. WashingServices University ofthe Health

August

13 and

received

September

3;

toJ.G.S.

are the private views of the of the Army, the Department

authors and of Defense,

are not to be construed as official or the Uniformed Services Univer-

Sciences.

1991

1087

Figures in the

1, 2. Typical left frontal region

meningioma. (1) CT scans that has high attenuation

of a 55-year-old before contrast

white man demonstrate material administration

geneously enhances afterward (b). Note the sharp margins and associated hyperostosis (arrowheads in a). (2a) Radiograph of a 42-year-old white woman with an enlarging shows marked hyperostosis (arrowhead). (2b) Contrast material-enhanced CT scan dense homogeneous enhancement.

brain. the

The cerebral

noid

wing

mas,

computed

strates sharply

1088

U

most common convexity, regions.

typical

In 72%-85%

tomography diagnostic

circumscribed

RadioGraphics

locations parasagittal, (CT) features,

Buetow

tamed

dural

without

of the overlying bone occipital protuberance depicts the mass with

attachment.

contrast

On

material,

scans

ob-

the mass

appears

as an area

of homogeneous

hyperat-

demon-

tenuation;

after

administration

of contrast

mass

Ct

broad-based

mass homo-

of meningioincluding

unilobular

U

include and sphe-

an extraaxial (a) and that

at

with

a

material,

a

(Figs

the 1, 2)

the

mass

(3,4).

images,

the

typical

include

a unilobar

homogeneously

On

magnetic features

mass

enhances

resonance

(MR)

of meningiomas

with

sharply

Volume

circum-

11

Number

6

d.

Figure

3.

Vascular

woman

with

meningioma.

a 6-week

history

Ti-weighted of headache

(a) and T2-weighted and

papilledema

around the tumor (arrow) that may be produced ated edema (* in b) is well seen on the T2-weighted tensity. (c) Selective external carotid arteriogram supplying

dural

the

tumor

attachment

scnibed

margins

and

an unusually

(arrowheads).

and

inward

dense

Fresh

by arteries

displacement

November

the

mass

1991

homogeneously

enhances

blush.

reflects

of

the cortical gray matter (5,6). On MR images obtained without contrast material enhancement, meningiomas are characteristically hypointense to isointense with Ti-weighted pulse sequences and isointense to hyperintense with T2-weighted pulse sequences (Fig 3) (6). On MR images obtained with gadolmnium,

and

the

demonstrates

tumor

Meningiomas 3),

itself

middle

Photograph

hypervascularity

nent

of the

meningeal cut

Associ-

increased

signal

artery

specimen

in-

(arrow)

shows

the

of the tumor.

persistent the

white

(jseudocapsule)

of the lesion.

exhibits

usually

and and

rim

in the periphery tumor

a dilated (d)

of a 34-year-old

a low-signal-intensity

or veins

image,

bleeding

(b) MR images

reveal

most

demonstrate

blush frequent

a promi-

on angiograms calvanial

hyperostosis of the adjacent be seen on plain radiographs, and MR images (Figs 1 2).

change

(Fig is

skull, which may as well as on CT

,

(5).

Buetow

et at

U

RadioGrapbics

U

1089

However, 15% benign or typical

or more of histologically meningiomas may exhibit

certain uncommon imaging features such as heterogeneous enhancement, large cysts, ring enhancement, hemorrhage, and fat attenuation values (3). In addition, meningiomas may also be found in less typical locations, away from the large dural sinuses and skull base where they most commonly occur. Such less frequent sites include the orbit (optic nerve sheath), the paranasal sinus, the choroid plexus (intraventricular), and the diploic space of the calvaria. It is important to recognize both the atypical locations and unusual imaging features of these common neoplasms in order to avoid misdiagnosis. This article highlights some unusual features of morphology and location for meningiomas, presents imaging findings that may suggest certain benign histologic variants and malignant meningeal neoplasms, and correlates imaging with gross pathologic findings where appropriate. U LOCATION Histologically, true meningiomas arise from meningothelial cells (arachnoid “cap” cells), and the tumors occur more frequently where these cells are most numerous. The arachnoid granulations or villi have large numbers of cap cells and therefore are a common site of origin

for

meningiomas,

especially

where

the

viii

are concentrated along the dural venous sinuses. Other sites of origin include the arachnoid associated with cranial nerves as they exit the cranial vault and even the choroid plexus (since the arachnoid participates in its formation). In fact, any meningothelial cell, whether intracranial, spinal, or ectopic, can potentially result in the formation of a meningioma. Excluding those in spinal locations, which constitute

approximately

12%

ofall

meningio-

mas, intracranial and juxtacranial meningiomas arise in the following locations in descending order of frequency: convexity (lateral hemisphere) (20%-34%); parasagittal

1090

U

RadioGrapbics

U

Buetow

et at

(medial falcine below

hemisphere) meningiomas the superior

(18%-22%) [5%J, which sagittal sinus

extend

to both sides);

cranial posterior torium

fossa (17%-25%); fossa (9%-15%), cerebelli (2%-4%),

ity

(5%),

sphenoid

(includes are located and usually

and middle

frontobasal including cerebellar

cerebellopontine

angle

(10%); the tenconvex(2%-4%),

clivus ( < 1%); intraventricular (2%-5%); orbital (< 1%-2%); and ectopic (< 1%) (4,7). Because complete surgical resection is the definitive treatment for meningiomas, the single most important feature regarding therapy is tumor location, as it substantially affects surgical accessibility. Consequently, it is important to recognize the potential atypical and

locations

proper U

of these

diagnosis

UNUSUAL

neoplasms

and

to ensure

both

treatment.

LOCATIONS

Cerebellopontine Angle Meningioma The meningioma is the second most common mass lesion of the cerebellopontine angle, with 13%-18% ofall neoplastic lesions in this location being meningioma (8,9). Less than 5% of all intracranial meningiomas occur in the cerebellopontine angle (8,9). The acoustic schwannoma, from which meningiomas must be distinguished, is by far the most common tumor in this region. Meningiomas, however, tend to be larger, more hemispheric in shape rather than spherical, and more homogeneously enhancing (Fig 4). Meningiomas may I

be associated with hyperostosis. They do not have a propensity to involve the internal auditory canal (which is a fairly constant feature of schwannomas) (10). .

Orbital

Meningioma

Orbital meningiomas account for less than 2% ofcnanial meningiomas but constitute 10% of all intraonbital neoplasms (5). Most of these tumors arise from the optic nerve sheath between the globe and the optic canal (5). They may produce diffuse thickening of the optic nerve, a well-defined and rounded mass, or even an eccentric lesion with an irregular bonden (Fig 5a). Calcification along the optic nerve sheath is highly suggestive of meningioma (Fig Sb).

Volume

11

Number

6

Figures

4, 5. (4) Cerebellopontine angle meningioma. (a) Contrast-enhanced CT scan of a 58-year-old woman shows a homogeneously enhancing, well-circumscribed mass in the left cerebellopontine angi e and a second smaller component in the left middle fossa. The fourth ventricle (*) is compressed and deviated from the midline. (b) Coronal T2-weighted MR image of a 66-year-old white woman demonstrates white

extraaxial

nature

of the meningioma

and

the mass

effect

on the brain

stem.

(5) Orbital

meningioma.

(a) Con-

trast-enhanced CT scan of a 57-year-old white woman with decreased vision in her left eye shows a lobulated mass surrounding the optic nerve and associated proptosis. At surgery, the tumor was found to extend near to, but not involve, the optic chiasm. (b) CT scan obtained with bone windows of a 47-year-old white woman with slowly progressive loss ofvision in her left eye demonstrates excessive calcification and thickening

around

November

the optic

1991

nerve.

Optic

nerve

sheath

meningioma

was proved

at surgery.

Buetow

et at

U

RadioGrapbics

U

1091

Figures

6, 7. Multiple meningiomas. (6a) Contrast-enhanced CT scan of a 75-year-old black woman who experienced loss of consciousness shows a carpeting of the left inner table of the skull and petrous

bone

by an extensive

frontoparietal

meningioma. There is associated hyperostosis (arrowheads) but no associated edema. Note the small right subfrontal and left tentorial meningiomas (*). (6b) Another scan obtained at a more cephalic level reveals the upper extent of the largest tumor, as well as an additional meningioma along the night parietal bone (arrow). Note the left-sided hyperostosis (anrowheads). (7) Selective external carotid artenogram of a 30-year-old white woman with headaches demonstrates three separate frontoparietal meningiomas (arrows). Each has a dense vascular blush.

7-

1092

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RadioGrapbics

U

Buetow

et at

Volume

11

Number

6

a. Figure

8.

En plaque

meningioma.

(a) Radiograph

b. of a 45-year-old

black

woman

shows

of the left parietal calvaria. Paget disease, chronic osteomyelitis, fibrous dysplasia, all possibilities in the differential diagnosis. (b) CT scan demonstrates the nodular of the calvaria on the left, indicating the extnaaxial location of the lesion. Without

were

.

not available,

Multiple

the tumor

cannot

be easily

distinguished

Meningiomas

from

S

extensive

and metastatic mass along bone-window

thickening

disease are the inner table scans, which

the hypenostosis.

En Plaque

Meningioma

In one series (1 1), CT demonstrated multiple tumors in about 9% of patients with intracranial meningioma (Figs 6, 7) This approaches the 16% frequency of multiplicity found in an autopsy series (2). As with solitary examples, multiple meningiomas are more commonly

En plaque meningiomas cloak the inner table of the skull, where they may infiltrate both the dura mater and underlying bone. On CT

seen mas

tosis

.

type

in women. are associated 2 (“central”

jonity

of patients

istic features Further quired giomas

tosis

Although multiple meningiowith neurofibromatosis neurofibromatosis), the mado

not

other

character-

as multiple research with genetic to determine whether

schwannomas. testing is remultiple menin-

are

neunofibroma-

type

inherited

without

2 Secondary the subanachnoid space explanation for multiple

November

have

such

1991

.

spread of tumor via is a less well-accepted meningiomas (1).

scans,

especially

those

obtained

trast material, it may the tumor itself from (Fig

8).

perostosis

The

has

extent

little

without

con-

be difficult to distinguish the associated hyperosof radiographic

relation

to the

hydegree

or

presence of bone invasion and may occur secondary to local hypervascularity (1,5). Penitumoral edema is less common with en plaque tumors.

MR

images

enhancement enable to be easily distinguished bone changes (5,12).

Buetow

obtained

this

et at

with

type from

U

gadolinium

of meningioma the associated

RadioGrapbics

U

1093

a.

b.

Figure

9.

seizures

quent

Intraventnicular shows

finding

Ti-weighted

tumor

U

RadioGrapbics

meningioma. globular

in intraventnicular (b)

and

coronal

(*) in the trigone.

peniventnicular rior choroidal arrow).

1094

a large

(a) Contrast-enhanced

of a 36-year-old

white

woman

with

enhancing

is associated

edema. (d) Left internal carotid artery (curved arrow) and mild

U

CT scan

mass in the region of the left trigone. Calcification, a fremeningiomas, was noted on unenhanced CT scans (not shown). Sagittal T2-weighted (c) MR images clearly demonstrate the low signal intensity of this

There

densely

Buetow

et at

hydrocephalus, arteriogram tumor blush

dilatation

ofthe

shows characteristic in the region of the

entrapped

temporal

enlargement ventricular

horn,

and

of the left antetnigone (straight

Volume

11

Number

6

#{149}#{149}_‘4”_’S_

+_

r:;4

Figures 10-12. Intradiploic meningioma. (10) Radiograph of a 34-year-old black man, who complained of a bump on his head and orbital pressure, reveals a central radiolucent lesion with partial loss of the outer table of the skull (arrows) and with extension into the frontal sinus. The tu-

mon arose within bone but had extended through the dura mater and involved the frontal sinus. (ii) Lateral image from an external carotid arteriognam of a 20-year-old reveals marked

man with hypenostosis

mild

frontal headaches of the frontal bone

and anterior aspect of the parietal bone. There is marked widening of the diploic space with penpendicular proved spaces brous

spiculation (arrowhead). Radiolucent areas at microscopic examination to be medullary of lamellar bone, filled with tumor cells, fitissue, and a few osteoclasts. (12) CT scan of

a 69-year-old white man, who complained bump on his head for the past 10 years, strates

. Intraventricular Intraventnicular tela

choroidea

plexus

itself.

bone

Meningioma meningiomas arise or the Approximately

stroma

from

of the 80%

the

choroid

arise

.

.

Ectopic

completely hyperostotic

mild

area

expansion

intraosseous reaction

within

the

right

of the diploic

meningioma was confirmed

parietal

space.

A

with marked pathologically.

in the

lateral ventricles with a preference for the left tnigone (Fig 9), 15% occur in the third ventnicle, and about 5% within the fourth ventricle (1 1 3) Overall, intraventnicular meningiomas account for approximately 2%-S% of intracranial meningiomas (4,7). Meningioma is the most common trigonal intraventricular mass in an adult (14).

,

an osteoblastic

with

of a demon-

Meningioma

These ectopic the intradiploic the

skull,

meningiomas space, from

in the

overlying

pananasal sinuses, in the from the parapharyngeal Theories to explain these dude derivation from the the cranial nerve sheaths cells disseminated during

may arise the outer skin,

inside

within table of the

parotid gland, and space (Figs 10-16). sites of origin inarachnoid around or from anachnoid the formation of the

Less than 1 % of meningiomas develop extradurally (this is exclusive of tumors that secondanily spread from intracranial sites) (15).

November

1991

Buetow

et at

U

RadioGrapbics

U

1095

C

Figure 13. Extracranial extension of meningioma. An asymptomatic 64-year-old white man struck his head, and radiographs showed a mottled lytic area in the right frontoparietal region with overlying spiculation and peniosteal reaction. A soft-tissue mass was also seen. (a) Right external carotid arteniogram helps confirm these bone changes and demonstrates the vascular capillary blush supplied primarily from branches of the superficial temporal artery (arrow). (b) Contrast-enhanced CT scan demonstrates the meningioma, prominent bone involvement with marked thickening of the calvaria, as well as extracranial soft-tissue extension (*). Coronal Ti-weighted (c) and T2-weighted (d) MR images show convex extension ofthe tumor, both intracranially

skull

the

1096

U

and

(ie,

extracranially,

ectopic

skull

base is seen

ryngeal

and

RadioGraphics

inclusions).

with

tension

which

secondary

in over

paranasal

one-third

sinus

U

Buetow

was

confirmed

Destruction

of

Meningiomas

intracranial

ex-

ered in locations far removed from the neunaxis including the mediastinum, lung, and adrenal glands. Possible explanations indude ectopic arachnoid cells and meningothelial differentiation from plunipotential mesenchymal cells (1).

of nasopha-

meningiomas.

et at

pathologically.

have

also

rarely

been

Volume

discov-

11

Number

6

Figures

14-16.

(14)

Ethmoid

meningioma.

1-year history of decreased visual sinus mass with infiltration and dial orbital wall. The radiologic might have a similar appearance. tamed with bone windows of a lobulated and partially calcified no intracranial component were

enhanced

CT scans

of a young

(15)

1991

Sphenoid

CT scan

and nasopharyngeal

77-year-old white man with mass within both sphenoid found. (16) Parapharyngeal

girl with

left nasopharyngeal space, infratemporal through the sphenoid bone. Note the in a). At surgery, tumor was discovered

November

Contrast-enhanced

ofa

20-year-old

black

man

with

a

acuity and proptosis of the right eye demonstrates an enhancing paranasal destruction of the ethmoid air cells. There is extension through the right mefindings are nonspecific, and other neoplastic or inflammatory conditions

a hearing

meningioma.

spontaneous epistaxis sinus compartments. meningioma. Axial

loss in the left ear reveal

fossa, and pterygoid fossa. The bone remodeling and hyperostosis in the left maxillary sinus, ethmoid

a large

Unenhanced

CT scan

ob-

demonstrates a smooth No bone destruction and (a) and coronal (b) contrast-

tumor

that

involves

the

tumor also extends intracranially ofthe maxillary sinus wall (arrows air cells, and orbit.

Buetow

et at

U

RadioGraphics

U

1097

Figure

17. Cystic meningioma. shows a right frontal meningioma has characteristics of a meningioma:

trast-enhanced the cyst rim all enhancing

CT scan (arrows), tissue

(a) Contrast-enhanced CT scan ofa 72-year-old woman with headaches and a large extratumoral cyst. Aside from the fluid-filled area, the lesion hemispheric, dural-based mass with prominent enhancement. (b) Con-

of another

which adjacent

patient

shows

similar

U ATYPICAL IMAGING FEATURES In general, the various imaging features of meningiomas may not accurately reflect the specific histologic subtypes of this common neoplasm, and the biologic and clinical behavion of meningiomas

does

with the different 5,16). Therefore, it is important pleomorphic

plasms, gioma

not

always

correlate

histologic variants (1,3from an imaging standpoint, to recognize

features

the

exhibited

so that an unusual is not confused with

variable by

and

these

neo-

appearing meninother intracranial

. Cystic Meningioma The term cystic meningioma has been used to describe two different morphologies: intratumonal cavities and extratumoral or arachnoid cysts. Therefore, the cysts can be located the

tumor

mass,

However,

either

centrally

or

ec-

centrically; outside and adjacent to the edge of the tumor; and, occasionally, inside the adjacent brain parenchyma. True intratumoral cystic meningiomas (Figs 17, 18), with large dominant fluid-filled cysts, are an un-

there

or neoplastic

is faint

tissue.

enhancement

Histologic

of

evaluation

necrosis

occur

much

8%-23% ofcases) gioma may have in that

more

frequently

(up

U

RadioGrapbics

U

Buetow

et at

to

(3-5). A large cystic meninan atypical clinical presenta-

they

are

more

common

in male

and pediatric patients; these unusual clinical features often contribute to a misdiagnosis of a cystic or necrotic glioma (17). Various explanations for cyst formation have been offered, including that intratumoral cysts are due to tumor necrosis or degeneration. A peripheral cyst, on the other hand, may represent either peripheral degeneration or an arachnoid cyst. Although the imaging

differentiation

between

a peripheral

(neoplastic) intratumoral cyst and an extratumoral (reactive) arachnoid cyst may be suggested when ring enhancement is seen sunrounding the fluid collection, histologic analysis,

cyst

wall,

addition, tion

demonstrating

may cysts

of fluid

neoplastic

be required may by tumor

result cells,

cells

in the

for confirmation. from

direct

from

Volume

In

secre-

absorption

of internal hemorrhage, or from loculated cerebrospinal fluid in scan tissue within adjacent to the meningioma (17).

1098

of

common variant. Benign meningiomas with heterogeneous enhancement that contain small nonenhancing areas of cystic change or

tion,

masses.

within

findings.

may be either a meningeal reaction to a meningioma is recommended.

11

on

Number

6

Figure 18. Cystic meningioma. Axial MR (C), and coronal enhanced CT (d) pears to be an extratumoral cyst (* in for neoplastic involvement of the cyst mass

November

such

1991

contrast-enhanced images

a). However,

wall.

CT (a), axial enhanced

of a 45-year-old

Note

the

man

curvilinear

the “dural

tail”

demonstrate enhancement

sign

(arrow

MR (b), coronal enhanced a meningioma with what (arrowhead)

in b), suggestive

ap-

is suspicious

of an extraaxial

as meningioma.

Buetow

et at

U

RadioGraphics

U

1099

d.

C.

Figure

19.

Lipoblastic

meningioma.

2-week history of seeing flashing lights lesion. The rim of the lesion is enhanced, Ti-weighted (b) and axial T2-weighted similar to that of subcutaneous fat. (d) color of fatty metaplasia.

(a) Contrast-enhanced and

difficulty and faint

(c) MR images Gross

specimen

. Lipoblastic Meningioma Lipoblastic meningiomas represent a variant in which there is a metaplastic change of meningothelial cells into adipocytes, through the accumulation of fat (mostly triglycerides)

1100

U

RadioGraphics

U

Buetowetat

CT scan

in reading intratumoral

demonstrate shows

white

a signal

against

their

cytoplasm

the

lipoblastic

either

a true

“collision”

gioma)

tumor

lies

in the

woman

within

the lesion

mass

and

the

(18).

The

(between

recognition

a

that is

yellowish

evidence

meningioma

intracranial

with

low-attenuation are seen. Sagittal

tissue

intensity

a well-circumscribed

within ing

of a 60-year-old

shows a well-circumscribed strands of enhancing

represent-

lipoma

or

fat

a menin-

and

a

of a spectrum

Volume

11

of

Number

6

7!

Figure

20.

progressive patible with

Lipoblastic meningioma. (a) Contrast-enhanced gait difficulty demonstrates a left frontoparietal fat) center and a thick enhancing rind. Note

central enhancing nodule of the middle meningeal is characteristic

of meningioma.

seen

mater

(arrows)

and

The ‘ ‘dimple’ ‘ in the center of the neovasculanity Photograph of the cut specimen shows the attachment yellow-white color typical of lipoblastic meningioma.

in a. the

appearance

of a fatty

tumor,

with

that (18). an imlow

negative attenuation on CT scans (Figs 19, 20) and a short Ti relaxation time with high signal intensity on Ti-weighted MR images (Fig 19) (19,20). Xanthomatous change in menin-

November

1991

(arrow) corresponds to the of the tumor to the dura

(C)

cells, ranging from typical meningothelial cells, through those containing various amounts of intracellular lipid, to cells have been transformed into adipocytes The lipoblastic meningioma may have aging

CT scan of a 36-year-old white woman with mass with an extremely low-attenuation (comthe small mound of hyperostosis (*) underlying the

of meningioma (arrow). (b) Right external carotid arteriogram shows enlargement artery that supplies the tumor. The spoke-wheel pattern of the fine radial arterioles

mound

of bone

‘‘

gioma can be differentiated histologically from the lipoblastic variant; however, both contain excess lipid, the nadiologic tinction

may

be

blastic meningioma the fatty regions ent, and do not (19).

Buetow

difficult.

However,

the

since dislipo-

may be suggested when are larger, are more confluhave prominent enhancement

et at

U

RadioGraphies

U

1101

Figure shows

men

.

21.

Hemangiopericytoma

homogeneously

from

ofthe

enhancing,

a different

Meningeal

patient

meninges

markedly

exhibits

lobulated

the characteristic

Hemangiopericytoma

Hemangiopericytoma

of the

(Fig

.

develop distant metastases (23,24). An unpublished study of 13 cases from the Armed Forces Institute of Pathology and a review of the literature indicate the following features are suggestive (but not pathognomonic) of a meningeal hemangiopenicytoma: a multilobulated contour, a narrow dunal base or ‘ ‘mushroom’ shape, large intratumoral vascular signal voids on MR images, multiple irregulan feeding vessels on angiograms, and bone erosion rather than hyperostosis (22,25). It has also been reported that prominent penitumoral edema and increased signal on T2weighted MR images (Fig 3) are more common in the syncytial and the angioblastic meningiomas (a category that includes hemangiopenicytoma) than in other types (i6,26). ‘

.

Peritumoral

masses

lobulated

U

RadioGrapbics

(a) Contrast-enhanced the

tumor

parietal

lobes.

CT scan (b)

Gross

speci-

surface.

However,

mild

to moderate

intraaxial

vasogenic edema is also seen around omas (which are extraaxial masses) 75% ofcases (7,27) (Figs 1-3). The edema can be problematic, since its may be incorrectly suggestive of an lesion (eg, gliorna). This problem is

meningiin up to finding of presence intraaxial com-

pounded when the meningioma is small and the surrounding edema is extensive. The cause of intraaxial penitumoral vasogenic edema associated with meningiomas is controversial. Some theories implicate active fluid production (secretion or excretion) by the tumor, with “flow” through the thinned contiguous cortex (28). Others have suggested that the tumor injures the brain mechanically (by means of direct compression) or ischemically (from parasitization of the contical

arteries,

veins,

or

compression frank

of the

involvement

of the

cortical dural

si-

nuses) Most likely, the edema is caused by a combination of different mechanisms. Reports about the importance of these factors have been conflicting (27,29,30). However, recent .

studies

have

found

poor

correlation

between

penitumoral edema and either the vascular supply of a meningioma or the presence of dural sinus invasion (27) Whatever the mech.

anisms,

the

degree

meningiomas size (5,27).

glioma,

metastatic

disease,

of

has

of penitumoral

little

correlation

edema

in

with

tumor

and

. Ring Enhancement As mentioned, meningiomas are usually fairly homogeneous masses, with homogeneous enhancement. However, they may have an atypical ringed appearance (Figs i7b, 18, 22, 23),

1 102

man.

indenting

Edema

edema within the white matter is a common feature of intraaxial like

tumor

abscess.

meninges

2 1) is an aggressive, highly vascular neoplasm that is commonly grouped with “angioblastic” or “malignant” meningiomas (21,22). However, hemangiopenicytoma of the meninges is a distinct nosologic entity arising from the vascular penicytes rather than from meningothelial cells; thus, it is not a true meningioma at all (23) These tumors generally recur more frequently and earlier than meningiomas, and they have a greater propensity to

Vasogenic the brain

in a 73-year-old

U

Buetow

et at

rather

than

occur

as a solid

Volume

mass.

This

11

Number

6

Figures

22, 23.

(22)

Ring enhancement

with

cystic

changes.

Unenhanced

of a 4-month-old infant with increasing head circumference show ternal calcification (arrow in a) and a low-attenuation center with mass does not enhance uniformly, compatible with cystic change.

fourth ventricle (arrowhead toma or cystic astrocytoma necrosis. (a) Contrast-enhanced demonstrates tral

November

necrosis

1991

ring in this

in a) and associated could be considered

enhancement histologically

hydrocephalus. in the differential

CT scan of a 35-year-old in a meningioma. (b) typical

Cut

(a) and enhanced

(b) CT scans

a large mass in the posterior a high-attenuation rim. The There is anterior displacement

In this age group, diagnosis. (23)

white man who surface of the

fossa with incenter of the of the

a necrotic medulloblasRing enhancement with

experienced loss of consciousness gross specimen illustrates the cen-

meningioma.

Buetow

Ct

at

U

RadioGraphics

U

1103

Figure 24. “Butterfly” meningioma. (a) and enhanced MR image obtained bilateral similar

extension and central to that of a ‘ ‘butterfly’

unusual

feature

cally

typical

can

be

‘

cavitation glioblastoma

seen

meningiomas

Contrast-enhanced parallel to the Reid from necrosis multifonme.

in both and

malig-

nant on aggressive histologic variants that may have cyst formation, hemorrhage, or necrosis. The peripheral enhancement represents the normal pattern for viable meningeal neoplasms,

and

crotic

the

region.

center

The

enhancing

zone

infarction,

necrosis

variants,

and

fluid may

true

such

cyst

ring with

blastoma

can 24),

multiforme

from

even which

(grade

U MIMICS Many atypical gross and meningiomas have been should also be recognized

mimic

neoplasms

chyma

If cere-

This

as

appearance

well

as

some

superfi-

may also exhibit a broad surface and homoge-

enhancement

For

such

is

thereby

example,

mimick-

hematologic

as leukemia

or

secondary

in-

of the central nervous system by lymphoma, which is a late manifesta-

of the

exxraaxial

on cysfalx

lesions

tumors the dural

contrast

tion

A con-

woman.

ing meningioma.

Hodgkin

an abscess. the

neous

non-

enhancement

or even

soft-tissue

cia! intraaxial contact with

tumor benign

a necrotic

white

volvement

ne-

histologic from

arises (Fig

bland

(i7,31).

with

growth

glioma

central

include

above)

a metastasis,

bilateral

the

or

formation

confused

a meningioma

terfly”

for

and

(see

be

avasculan

in aggressive

meningioma easily

tic glioma, bri,

causes

vary

accumulation

vexity

is an

in a 73-year-old

ial

histologi-

in some

CT scan obtained at 25#{176} above the Reid baseline baseline (b) demonstrate a faix meningioma with

disease,

will

spaces (Fig

25)

typically

rather (32).

cult to differentiate dural-based masses oma include dural from breast cancer toma.

than Such

involve the

the

brain

cases

may

parenbe

diffi-

from meningiomas. Other that may imitate meningiand calvarial metastases and metastatic neuroblas-

a “but-

is usually

a glio-

4 astrocytoma).

imaging features of presented here. It that other extraax-

U CONCLUSION Meningioma is the most common primary neoplasm of the central tern. The diagnosis of meningioma uncomplicated when the tumor location

and

has

characteristic

nonglial nervous sysis relatively is in a typical radiologic

find-

ings. However, it must be remembered that meningiomas may occur in unusual locations and with misleading or atypical imaging featunes.

1104

U

RadioGraphics

U

Buetow

Ct

at

Volume

11

Number

6

Figure

25.

Mimics.

(a) Contrast-enhanced

CT

scan of a 14-year-old black boy with headaches and ataxia reveals a broad-based, homogeneously enhancing mass in the posterior fossa and secondary obstructive hydnocephalus. The mass had uniform low attenuation on unenhanced CT scans and proved to be granulocytic sarcoma (chloroma). This

mass

may be indistinguishable

from

a meningioma

or lymphoma involving the skull or dura mater. Unenhanced (bone window) (b) and contrast-enhanced (c) coronal CT scans of a 22-year-old black woman who presented with seizures show an extraaxial mass with broad-based dural attachment. There is homogeneous enhtncement and associated hyperostosis. A biopsy ofan a.xillary lymph node revealed Hodgkin lymphoma.

Rohninger M, Sutherland GR, Louw AAF. Incidence and clinicopathological

C.

tunes

of meningioma.

J Neurosung

DF, Sima fea1989;

71:

665-672.

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for

Answers The answers September 1.

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11

Number

6