CT and MR Imaging of the Central Skull Base Part

2. Pathologic

FredJ.

Lame,

Lyn

Spectrum1

MD

Nadel,

MD

Ira

F. Braun,

MD

The

radiologist

must

have

my and the pathologic

a thorough

spectrum

knowledge

of the skull

of the

base

norma!

anato-

to determine

the ex-

tent of abnormality and to help plan the surgical approach. The authors describe and present examples of congenital, benign, and malignant lesions that affect this region, including cephalocele, fracture, fistula, juvenile angiofibroma, meningioma, chordoma, pituitary adenoma, chondrosarcoma, nasopharyngeal carcinoma, and rhabdomyosarcoma. Metastatic, infectious, and other miscellaneous processes are also discussed. Imaging strategies with computed tomography and magnetic resonance imaging to aid in the diagnosis are suggested. INTRODUCTION

I

With

surgery

o!ogists cesses

for treating

are challenged in this region.

deep-seated

lesions

to determine In Part 1 , we

more presented

of the skull

base

now

available,

radi-

accurately the extent of disease the embryologic development

proand

the anatomy of the central skull base and floor of the middle cranial fossa as seen at gross, computed tomographic (CT) , and magnetic resonance (MR) imaging cxamination. In Part 2 we present examples of congenital and acquired lesions, both benign and malignant, that affect this region and suggest imaging strategies for the evaluation of central skull-base lesions. ,

CONGENITAL/DEVELOPMENTAL

I

Cephaloceles

account

phalocele midsagittal ninges

for

LESIONS

1 O%-20%

of all craniospinal

is a protrusion of intracranial defect in the calvaria and and

the

subarachnoid

space,

contents dura mater. while

malformations

(1)

.

A cc-

through a congenital, usually A meningocele involves only

an encephalocele

contains

brain

me-

as

well.

Abbreviation: Index

CSF

terms:

#{149} Skull,

Skull,

primary

1

From

the

the 1989 acceptedjune

Department

10:797-82

#{149} Skull,

CT,

12.121

1

#{149} Skull,

injuries,

12.4

#{149} Skull,

MR studies,

12.1214

1

ofRadiology,

VA 23298-0615 scientific 14. Address

©RSNA, 1990 Part 1 ofthis article

12.146

12.3

1990;

RSNA

fluid

abnormalities,

neoplasms,

RadioGraphics

Richmond,

cerebrospinal

(F.J.L., assembly. reprint

appeared

Division L.N.),

and

Received requests

in theJuly

1990

ofNeuroradiology, the

Department

February to FJ.L.

15,

Medical of Radiology, 1990;

revision

College

ofVirginia,

Box

Baptist

Hospital

of Miami

requested

March

21 and

615,

MCV (I.F.B.).

received

Station, From May

29;

issue.

797

Figure

1.

Basal cephalocele

craniopharyngeal

with

canal

recurrent

diograph

bouts

of the

with

of meningitis.

skull,

persistent

in an 8-year-old

child

(a)

submentovertex

Plain view,

radem-

onstrates a well-defined area of decreased opacity surrounded by a thin rim of cortical bone projected over the skull base (arrow) Axial CT scan (b) photographed with bone window and coronal CT scan (c) photographed with soft-tissue window reveal the presence of a persistent cranio.

pharyngeal

canal

(arrow)

and

midsagittal

(e)

images through the central herniation of the pituitary

skull gland

pharyngeal (arrow)

the sphenoidal

Coronal

(d)

canal

through

in the

sphenoid

bone.

Ti -weighted

MR

base demonstrate into the cranio-

defect

Note the proximity of the pituitary gland to the roof of the nasopharynx. (Courtesy of Dr Lakshmana Das Narla, Medical College of Virginia, .

Richmond.) a.

d.

798

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Figure 2 Biopsy-proved encephalocele in a 35year-old man who underwent CT for evaluation of headache. Axial (a) and coronal (b) CT scans through the central skull base and sphenoid sinus reveal the presence of a soft-tissue mass within the left sphenoid sinus (arrow) The mass involves the base of the pterygoid plates on the left in the region of the Vidian canal. A smooth, wellcircumscribed defect is suggestive of a benign .

process.

The aperture is smooth of cortical bone. Basal mate!y 75% for around

and

defined

cephaloceles account 1 0% of cephaloceles,

occipital the

forms

nose

and

for approxicompared with

and

orbit.

by a rim

1 5% for those Basal

cephalo-

celes are subdivided into five major categories depending on the site of the defect: (a) sphenopharyngeal,

through

the

sphenoid

body; (b) sphenorbital, through the supenor orbital fissure; (C) sphenoethmoidal, through sphenoid and ethmoid bones; (d) transethmoidal, through plate; and (e) sphenomaxillary, maxillary sinus (2). Cephaloceles may occur

as a mass

nose, nasopharynx, tion of the orbit. basal cephalocele

or posterior porcommon type of through a defect

mouth, The most protrudes

the

cribriform through

in the

in the sphenoid bone as a pharyngeal which may cause airway obstruction as a site of cerebrospinal fluid (CSF)

rhea

tension

tion in the patient suspected of having a ccphalocele. The bone margins of the defect, as well as the soft-tissue component, are easily

of cephaloceles

through

the

sphe-

noid bone, however, has been attributed to persistence of the craniopharyngeal canal (Fig 1) (2) An additional cause is a developmental failure of the multiple and complex sphenoid ossification centers, with resultant .

herniation

through

the

defect

The dura mater is usually the periosteum

of the external

the defect (3) phalocele may sues, depending

the specific

.

(Fig

2)

(2).

continuous

with

opening

of

The external aspect of the ccbe covered with various tison the origin and location of

ca!varial

defect.

The

area

of

meningitis

mass, and act rhinor-

Most cephaloceles are thought to represent a failure of neural tube fusion (1) Ex.

and

the

(3).

CT of the skull base can be used for evalua-

recognized small dose

before

(Fig 1). The of intrathecal

CT would

instillation contrast

of a material

aid in the differentiation

a simple meningocele cele. In the instance

from an encephaloof an encephalocele,

cortical

in contrast

would should

sulci

bathed

be evident. MR imaging, obviate more invasive

the evaluation ofthe lesion.

of the soft-tissue

of

material however, procedures

in

component

bone dehiscence usually occurs at a suture or in an area where several bones coalesce.

September

1990

Lame

et al

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RadioGraphics

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799

.4p__

‘: : ;

3c. Figures

4. 3, 4.

(3)

Cavernous carotid fistula in an 1 8-year-old man after a motor vehicle accident. Axial CT scans photographed with soft-tissue (a) and bone (b) windows show subarachnoid hemorrhage and cxtensive basilar skull fracture, which extends obliquely along the sphenoid bone (straight arrows) across the cavernous sinus and into the petrous tip (curved arrow) (c) Lateral subtraction view from a left carotid angiographic study reveals a cavernous carotid fistula. Contrast material from the arterial system has cx.

travasated

into

the

cavernous

row) . (4) Multiple skull-base with superior orbital fissure

base reveals

multiple

sinus

(straight

fractures syndrome

fractures

(small

arrow)

and

subsequently

into

arrows)

associated

with fluid

I

RadioGrapbics

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Lame

et a!

petrosal

sinuses

accident. CT scan

in the ethmoid

Mu!tiple fractures causing narrowing of the orbital apex and superior orbital seen, as is a fracture involving the forarnen ova!e (large straight arrow).

800

the

in a 23-year-old man after an automobile and multiple crania! nerve deficits. Axial

fissure

(curved

and sphenoid (curved

Volume

ar-

He presented through the skull

10

sinuses.

arrow)

are

Number

5

I

.

TRAUMA

optic

Fractures

fracture. In instances ture, patients usually

Skull-base extensions most

fractures most of cranial-vault

common

locations

petrous temporal the frontal bone, Fractures

affected

of the

sphenoid

with

other

and

in approximately

with skull-base sphenoid bone

include

bone

are

on plain

radiographs

.

central skull to fracture, through its (5) These to recognize

attachments

typically due

lowing signs: matotympanum,

are usually

(5) While the to be relatively well

by its position in the it is particularly vulnerable as the lines of force can extend

osseous

of

injuries

base,

fractures

the

1 5% of patients

fractures appears

multiple

as

surface (4).

craniofacial

protected

ed clinically

occur The

bone, the orbital and the basiocciput

associated occur

commonly fractures.

.

difficult

and to one

are usually or more

CSF otorrhea mastoid

suspect-

of the

fol-

or rhinorrhea, region ecchymosis

he-

(Battle sign), periorbital ecchymosis (“mccoon eyes”) , or cranial nerve deficits. Anosmia and cavernous carotid fistula may also develop (Fig 3) Additionally, many muscles insert into or originate from the sphenoid bone, making muscular dysfunction an important sequela of trauma. Problems with oc.

nerve

damage

associated

with

canal

of sphenoid wing fracpresent with various

combinations of motor and sensory disturbances referable to the regional cranial nerves (Fig 4). Axial, thin-slice, high-resolution CT is the obvious method of choice for initial evaluation in patients presenting with skull-base fractures. In instances of suspected CSF leak, a study that employs water-soluble intrathe-

cal contrast material dicated (see below).

.

CSF

to define

the leak

is in-

Fistula

The most common cause of CSF fistu!a is skull-base trauma, and fistulization occurs in 2% of unselected head injuries (6) Fractures through the frontoethmoidal complex and middle cranial fossa are the most common Icsions associated with CSF leaks. The onset of leakage usually occurs within 48 hours of trauma and is usually unilateral. Anosmia is seen as a concomitant symptom in 78% of cases. Tumors, especially those arising from .

the pituitary

gland,

are the most

common

nontraumatic cause of leakage, while congenital anomalies, such as encephaloceles, are also implicated (6) Traumatic leaks are .

ular

motility,

ing,

and

be seen tures

eustachian

(5)

.

The

traversing

particularly Trauma may

mastication,

result

September

speech,

tube

many the

vulnerable to the body

may

neurovascular

sphenoid

bone

fluid

while

struc-

flow

bone leak

usually

also

are also

to injury. of the sphenoid

in a cerebrospinal

1990

function

swallow-

scanty

the

and

and

tend

nontraumatic

may

fection

is high,

treated

cases

persist

to resolve

types

for years.

occurring

in

have

The

in 25%-50%

1 week,

a profuse

risk

of inof un-

(6).

or

Lame

et a!

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b. Figure

raphy

5. Traumatic in a 25-year-old

through the sphenoid uble contrast material.

CSF fistu!a is demonstrated by water-soluble contrast material-enhanced man with persistent CSF rhinorrhea and recurrent meningitis. Coronal

sinus were

obtained

before

(a) and after (b) the intrathecal

cisternogCT scans

instillation

of water-sol-

A mass with attenuation values of soft tissue (arrow in a) is seen involving the right lateral floor of the sphenoid sinus. After contrast enhancement increased attenuation is seen in this region, consistent with the accumulation of contrast material (curved arrow in b) This finding confirms the presence of a CSF fistula. Note also the presence of contrast material within the suprasellar cistern (small arrows in b) outlining the chiasm and vascular structures. The fracture site was not identified. .

Locating

the

fore surgical phy,

leakage

site

intervention.

is mandatory

be-

CT cisternogra-

with

its more accurate depiction of the site of injury, has replaced the radioisotopic method of evaluation in the patient presenting with a CSF leak (7) Usually, the latter procedure is only successful in demonstrat.

ing the fistula if the patient has an active CSF leak at the time the study is performed. Patients are scanned with use of high-resolution, thin-section CT in the coronal plane, cither through the cribriform plate region or through the sphenoid sinus, depending on the area of clinical interest, before the instillation of contrast material. The CT scan is scrutinized for areas of bone dehiscence. A low dose of intrathecal contrast material is then instilled into the lumbar subarachnoid

space,

and

the

lar fashion.

patient

The

are compared to the

BENIGN

.

Juvenile

material

lesion

RadioGrapbks

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Lame

et a!

due

5).

is a highly that

originates

vascular, in either

locally the

nasopharynx or the posterior nares of male adolescents. It accounts for approximately 0.5% ofall head and neck neoplasms and is the most common benign tumor of the nasopharynx (8). Patients usually present with

nasal

obstruction,

staxis,

The site

and,

less

recurrent commonly,

of origin

of the nasal

I

(Fig

scans

differences

Anglofibroma

may involve areas proper, specifically

802

in a simi-

postcontrast

TUMORS

The angiofibroma invasive

and

for attenuation

contrast

I

is rescanned

pre-

is usually

and

severe

epi-

facial

deformity.

broad

based

and

outside the nasopharynx the posterolateral wall

cavity.

Volume

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b.

a.

6. Juvenile nasopharyngeal angiofibrorna in a 1 2-year-old child in whom a nasopharyngeal mass was noted at adenoidectomy. (a) Axial CT scan shows a tumor within the left nasal fossa (t) with lateral extension through the widened pterygopa!atine fossa (*) into the infratemporal fossa (b lack arrow) . Note the characteristic anterior displacement of the posterior wall of the maxillary antrum (white arrow) . (b) Coronal contrastFigure

:

--

I..,-.

I

.1_ -

-‘,-

enhanced the skull

study reveals tumor extending through base (*) into the sphenoid sinus with cxtension into the cavernous sinus (arrow) . (c) Latera! subtraction view from an internal carotid artery angiographic study reveals the supply to this 4

juvenile angiofibroma via dural branches of the cavernous carotid artery (arrow) , a finding consistent with tumor invasion of the cavernous sinus.

C.

Although it is histologically benign, the !esion can be highly aggressive and locally invasive. Extranasopharyngeal spread at the time of presentation is not uncommon. These lesions may also spread to the retroantra! region via the pterygopalatine fossa and thereby anteriorly displace the posterior wall of

present lesion

in nearly two-thirds of cases, as the violates the roof of the nasopharynx 6) This tumor may also extend laterally

(Fig into the

.

infratemporal

may spread through regional paranasal well (8).

fossa.

Angiofibromas

the natural ostia sinuses to involve

of the them as

the maxillary antrum (Fig 6). Once the tumor gains access to the pterygopalatine fossa, it may spread to the cranial fossa. Sphenoid

September

1990

orbit sinus

and the invasion

middle is

Lame

et at

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803

a.

b.

Figure

Juvenile nasopharyngeal angiofibroma in a 1 4-year-old male adolescent is. Midsagittal (a) and parasagittal (b) Ti -weighted MR images demonstrate a large and nasopharynx (*) , with posterior growth and involvement of the sphenoid sinus the base of the sphenoid bone (arrow in a) The parasagittal image (b) reveals the region of the cavernous carotid artery (arrow in b) within the cavernous sinus. The 7.

.

termediate

compared

with

CT demonstrates ing soft-tissue mass

that

muscle.

a homogeneous, enhancexpanding the pterygo-

palatine fossa (Fig 6) This termediate signal intensity MR images compared with .

perintense

of fat and

fat and

neoplasm has inon Ti -weighted the relatively hy-

the relatively

with recurrent epistaxmass in the nasal fossa due to destruction of mass coursing up to the signal intensity is in-

hypointense

ficult to recognize on MR images, the soft-tissue mass itself and the extent of its anatomic involvement are most easily appreciated with the use of this modality (Fig 7) (10).

.

Meningloma

muscle (Fig 7) Discreet punctate areas of hypointensity, presumably secondary to its highly vascular stroma similar to the effect

Meningiomas are typically that arise from arachnoida! ninges. They usually occur

seen other

the ages of 20 and 60 years and account approximately 1 5% of all primary brain

.

While

in MR images of paragangliomas and vascular neoplasms (9) , can be seen. small

areas

of bone

destruction

are dif-

mors. While they tally or along the volvement of the

benign tumors cells of the mein adults between

for tu-

are often located parasagitcerebral convexity, inskull base is not uncom-

mon.

804

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a. b. Figure 8. Meningioma in a 40-year-old woman with decreased visual acuity in the right eye. (a) Axial contrast-enhanced CT scan photographed with soft-tissue window demonstrates a large calcified lesion emanating from the media! sphenoid wing on the right (*) The enhancing soft-tissue component (arrow) is seen peripherally. (b) CT scan photographed with bone window reveals that the calcified portion of the meningioma (*) is adjacent to the anterior clinoid process (arrow). .

Sphenoid wing meningiomas can be gorized into hyperostotic meningioma plaque, those arising from the middle of the sphenoid ridge, and those arising the c!inoids processes. The en plaque usually

sive,

is accompanied

unilateral,

by slowly

painless

cateen third from variety

progres-

exophthalmos.

(Figs

8, 9) compress

temporal the usual mas

the

regional

frontal

and

lobes. Headache and seizure are presenting complaints. Meningio-

principally

involving

the

medial

wing

tend to encase the carotid and middle cerebral arteries and compress the optic nerve and chiasm, as well as the regional parenchy-

Headache, numbness in the distribution of crania! nerve V1 or V2, and seizures may occasionally be seen (1 1) Meningiomas arising .

from

the middle

September

1990

third

of the sphenoid

wing

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Figure 9. Meningioma in a 42-year-old with decreased visual acuity and seizures. al contrast-enhanced

sphenoid cavernous pontine sity (b)

CT scan

reveals

woman (a) Axi-

a right-sided

wing meningioma (*) extending to the sinus, middle crania! fossa, and precistern infratentorially. and T2-weighted (c)

Axial proton denimages reveal a mass

(arrow) that shows only a slight increase in signal intensity compared with that of the regional brain parenchyma. The lesion is much less conspicuous on the MR image compared with the CT scan. Axia! Ti -weighted images obtained before (d) and after (e) administration of gadopentetate dimeglumine (Magnevist; Berlex, Wayne, NJ) . The mass (arrow)

weighted intensely agent.

on the

non-contrast-enhanced

image is inconspicuous after the administration

T 1-

but enhances of contrast a.

b.

806

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et al

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.4#{149};-.4 ,,_:

U

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H-

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.

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Figure

10.

visual

loss.

‘,‘

.

,‘

-7

,

-

4

. .

.

.14

.

Meningioma

in a 65-year-old

Contrast-enhanced

axial

(curved

arrow

in b)

.

Sagittal

woman

CT scans

show a homogeneously enhancing mass noid body is seen, including the borders process

...

.-., .

#{149}

-

,

,

who

presented

photographed

with

with

anosmia

soft-tissue

and progressive (a)

and bone

bilateral

(b)

windows

in the suprasellar region (arrow in a) Hyperostosis of the spheof the optic foramen (straight arrow in b) and anterior clinoid .

Ti -weighted

MR images

obtained

before

(c)

and

after

(d)

administra-

tion of gadopentetate dimeglumine reveal an isointense enhancing suprasellar mass (*) extending into the sella turcica and along the planum sphenoidale (arrow) The mass is fairly isointense to gray matter on the Ti -weighted images. Inhomogeneous intensity of the sphenoid sinus component represents a combination of hyperostosis and retained secretions. .

ma. may

Meningiomas of the planum sphenoidale grow subfronta!ly and posteriorly into

the sella blistering

September

turcica of the

1990

and

clivus.

planum

In addition sphenoidale,

ostosis may also involve multiple portions of the central sphcnoid bone and produce van-

to

ous

hyper-

lems

cranial (Fig

nerve

deficits

and

visual

prob-

10).

Lame

Ct a!

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Figures 11, 12. (11) Meningioma in a 2 i-yearold woman with sensory disturbances along the course of the fifth cranial nerve. Coronal contrastenhanced CT scan reveals an enhancing lobular mass in the floor of the left middle cranial fossa (*) extending exocranially through the skull base via a widened foramen ovale (arrow) into the region of the parapharyngeal space. (12) Meningioma in a 55-year-old

woman

with

decreased

visual

acuity and facial pain. (a) Axial contrast-enhanced CT scan through the middle cranial fossa demonstrates a large enhancing lesion occupying the middle cranial fossa (*) and extending posteriorly into the intratentorial region, causing brain stem distortion (straight arrow) Note involvement of the sphenoid body (curved arrow) (b) Another scan reveals extension of this neoplasm inferiorly through the skull base into the pterygo.

.

palatine

fossa

(arrow)

(large

*) , and

carotid

sheath

and

ryngeal

space

(small

this

lesion

and

posteriorly

would

the

into

upper *).

include

infratemporal

the region

fossa

of the

reaches of the paraphaDifferential diagnoses of a malignant process.

12a.

Because arachnoid cells can be found accompanying cranial nerves, it is not surpnising that meningiomas can be found adjacent to and traversing various skull-base foramina (1 2)

erosion ulating structive

.

Although these meningiomas can cause of the foramina, a characteristic simschwannomas (Fig 1 1), grossly dechanges in the skull base may also

be seen, (Fig

808

I

RadioGraphics

12).

as these Indeed,

I

tumors

extend

in these

Lame

et a!

instances,

exocranially it may

be difficult malignant Smaller

to distinguish processes. meningiomas

these are

lesions

usually

from

best

im-

aged with CT. Focal areas of hyperostosis (which may be the only abnormality noted) are easily seen with the use of bone windows (Figs 8, 1 0) The soft-tissue component, when present, usually enhances intensely a!ten the administration of contrast material. Meningiomas frequently have relaxation .

Volume

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13.

Meningioma

in a 38-year-old

man

ieizures. (a) Contrast-enhanced axial CT eveals an enhancing mass (arrow) adjacent left anterior clinoid process. The non-connhanced study (not shown) revealed that Liss was not calcified. On axial Ti -weighted id T2-weighted (c) MR images, the relaxc haracteristics of the tumor (arrow) are sufkly similar to those of surrounding brain that mor

ass

and

brain

are barely

distinguishable.

is somewhat better seen d image. No parenchymal

on the T2edema is seen.

a.

b.

times

C.

similar

to that

of brain

parenchyma;

therefore, MR imaging may be relatively insensitive to their presence (Figs 9, 13). Ti-weighted images should be carefully scrutinized for distortion of anatomy, while areas of parenchymal hyperintensity (caused

September

1990

by brain weighted

edema) images.

should be looked The administration

magnetic contrast material will ic enhancement of these lesions should

ningiomas

be used

in the

for

on T2of pam-

cause dramatand therefore

MR investigation

of the skull

Lame

base

(Figs

et a!

of me-

9, 10).

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Figure 14. Chordoma in a middle-aged woman (a) Midsagittal Ti -weighted image demonstrates that

is hypointense

to isointense

relative

with symptoms indicating brain a destructive lesion (*) involving

to brain.

The

mass

extends

stem dysfunction. the central skull

anteroinferiorly

to involve

the

base roof

of

the nasopharynx (straight arrow), inferiorly to involve C- 1 (curved white arrow), and posteriorly to involve the brain stem (curved black arrow) (b) Axial T2-weighted image of a second patient demonstrates prolongation of the T2 relaxation time of a diva! mass (*) (Courtesy of Gordon Sze, MD, Yale University School of Medicine, New Haven, Connecticut.) .

.

S Chordomas account for less than i% of all intracranial tumors and 3%-4% of all primary bone tumors (i 3). They occur at any age, a!though most occur in the craniovertebral region in patients between the ages of 20 and 40 years, in contrast to sacrococcygeal chordomas, which occur at a peak age of 40-60 years. Sacrococcygeal chordomas more cornmonly affect men, but the craniovertebral chordomas affect men and women equally (1 4). These tumors are histologically benign, although they are regionally invasive and have a poor prognosis. A few are truly malignant and have distant metastases (i 5).

More

than one-third

the region clivus and synchondrosis

extend

of chordomas

occur

of the skull base, usually in the related to the spheno-occipital (1 3) These lesions typically .

inferiorly

into

the nasopharynx

and

may occasionally reach the nasal cavity and maxillary antrum (i 4) They arise in residual remnants of embryonic notochord, and the relationship of these neoplasms to this par.

810

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in

ticular region of the skull base is easily cxplained by the embryologic development of the notochord in this region. Orbitofrontal headache, visual disturbances, ophtha!moplegia, and ptosis are common presenting symptoms. Cranial nerves V, VII, and VIII are affected next, and pituitary or brain stem abnormalities may be present with intracranial spread. These lesions grow slowly; however, the prognosis is considered poor. Because of their infiltrative growth pattern, there is an almost i 00% recurrence rate despite radical surgery (i 4) The location of the neoplasm makes complete removal almost impossible, and large doses of radiation are required because chordomas are radioresistant (i 4). On radiographs, chordomas appear with .

bone

destruction,

which

can be associated

with

a soft-tissue mass. They commonly contam areas of calcification and bone fragments. The extent of bone destruction is best demonstrated with the use of CT and typically involves the clivus but may extend into the petrous apices and sphenoid bone (i 6). The soft-tissue component may enhance when contrast material is administered. MR

Volume

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Figure 15. a 38-year-old

rhea,

Invasive

benign

woman

with

pituitary

adenoma

amenorrhea,

in

galactor-

and

hyperprolactinemia. Midsagittal (a), (b), and coronal (c) Ti -weighted images reveal a mass (*) involving the sphenoid body that is isointense relative to brain. The mass extends inferiorly to the nasal fossa and nasopharynx (straight arrow in a) , posteriorly to involve the clivus (curved arrow in a), and laterally to envelop the cavernous carotid artery (arrow in b) and invade both cavernous sinuses (arrows in C). A sphenoid sinus malignant neoplasm or chordoma would also be included in the differential diagnoses. parasagittal

imaging, rate

however,

assessment

provides of the

extent

the most

accu-

of disease,

does in many other neck. The majority

areas of the head and of chordomas appear

isointense

to brain

relative

parenchyma

as it

on

Ti-weighted images and hyperintense on T2weighted images, although some tumors can appear inhomogeneously hyperintense on Ti-weighted images (Fig i4) (i6,i7).

.

Pituitary

Tumors tumors account for approximately i 5% of a!! intracranial neoplasms. The majority of pituitary tumors are adenomas. These lesions are usually slow growing, histologica!!y benign, and confined to the sella turcica (i 8). Some lesions, however, may grow

Pituitary

September

1990

more rapidly, display invasive tendencies, and give rise to symptoms such as headache and visual disturbances. Pituitary adenomas are classified according to size-with microadenomas being less than and macroadenomas greater than i cm-and endocrine features (1 8) They can secrete abnormal amounts of growth hormone, prolactin, adrenocorticotropic hormone, thyroid-stimulating hormone, folliclestimulating hormone/luteinizing hormone, or multiple hormones or can secrete none at all, but most are prolactinomas. Superior extension into the suprasellar cistern, lateral extension into the cavernous sinuses, and inferior extension through the skull base into the sphenoid sinus and nasopharynx can be seen on sagittal and coronal .

MR images

(Fig

15).

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,

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.

‘

#{149}

.

.-

.

.

--

Figure 16. Chondrosarcoma in a 65-year-old man with epistaxis and facial pain. (a) Axial CT scan photographed with bone windows reveals the presence of a midline destructive lesion involving the sphenoid body and extending anteriorly to the ethmoid bones and nasal fossa. An area of increased attenuation (arrow) , which may represent tumor calcification, is seen within the mass. -L

..

.‘1,

-‘1. .a

-

-‘

The

finding

suggests

the

diagnosis

of chon-

drosarcoma. (b) Axial Ti -weighted MR image obtamed at the same level as in a demonstrates a relatively homogeneous midline mass (*) that is slightly less intense than brain and associated destruction of the clivus (arrows) The previously noted area of increased attenuation, believed to represent tumor calcification in a, is inconspicu.

ous. (c) Midsagittal a destructive mass

Ti-weighted in the midline

MR image shows of the ethmoid

bones and nasal fossa extending posteriorly and causing destruction of the sphenoid body and clivus (*) Midsagittal image is ideal for demonstrating extent of disease.

C-

.

I

MALIGNANT

TUMORS

. Chondrosarcoma Chondrosarcornas stitute 6.7% of all rence (1 9) These .

of the reported lesions

head and neck consites of occurmay arise from car-

tilage, endochondral bone, or primitive mesenchyma! cells in the brain or meninges. Intracrania!!y, the most common locations for these lesions are adjacent to the sella turcica, in the cerebellopontine angle, and near the convexity (10). Parasellar lesions occa-

812

I

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sionally typically

extend spread

through by local

the skull invasion.

base and Even

when removed surgically, chondrosarcomas can recur. Systemic metastases are infrequent and usually occur only with an aggressive variant. The most common bone changes are a combination of erosion and destruction, usu-

Volume

10

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5

.I

Figure 17. Nasopharyngeal carcinoma in a 1 7-year-old male adolescent with nasal stuffiness. Ti -weighted coronal (a) and parasagittal (b) images reveal a large nasopharyngeal carcinoma that has spread to the parapharyngeal space (large *) and extended superiorly through a widened foramen ovale (arrow) to involve the middle cranial fossa (small *). These imaging planes are especially advantageous in the evaluation of transcranial tumor spread.

ally with a narrow zone of transition. Calcification of the matrix is a hallmark of these lesions, similar to that seen when these lesions occur in more common locations (20). MR imaging is best suited to demonstrate

the extent

of the disease.

CT, however,

still

retains an important complementary role for the evaluation of calcification, which may be helpful in the differential diagnosis. CT also helps in the evaluation of subtle bone erosion (Fig i 6).

.

Nasopharyngeal

Carcinoma

Nasopharyngeal carcinoma (squamous cell) accounts for 0.25%-0.5% of all malignant tumors in whites (i 0) There is, however, a .

distinct racial predisposition in the Chinese population. Men are afflicted more often than women, with a mean age of occurrence in the 40s. Due to their location, these lesions often remain asymptomatic for a long time, resulting in a delay in diagnosis. Nasopharyngeal carcinomas spread primarily by infiltrating neighboring regions rather than by expansion (2 i) Extension to and invasion of the skull base is a common mode of spread of this malignant neoplasm, and patients may present with involvement of the skull base.

Intracranial spread of carcinoma of the nasopharynx may involve cranial nerves III, IV, and VI, as well as V1 and V2. The fifth cranial nerve is the earliest and most commonly affected, producing numbness and subsequent pain along the distribution of its various branches. The next most commonly involved nerve is the abducens nerve, causing a lateral rectus palsy, resulting in dip!opia (i 0). Nasopharyngea! carcinomas have a homogeneous signal intensity similar to that of the adjacent mucosa on MR images. This signal intensity is intermediate between that of fat and muscle. These lesions, especially the smaller ones, are much more easily discerned on MR images than on CT scans. The superior contrast resolution of MR imaging allows one to locate more accurately the lesion and define its extent, especially involvement of adjacent muscle. Although axial images are used for initial localization, imaging in the corona! plane is mandatory to rule out transcrania! tumor spread (Fig i 7) (10).

.

September

1990

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Figure 18. Rhabdomyosarcoma of the nasopharyn.x with extension through the skull base in a 1 2-yearold boy with restriction of ocular motion and nasal stuffiness. Coronal (a) and axial (b) Ti-weighted images reveal a mass within the nasopharynx (large *) , with skull base destruction and invasion of the left cavernous sinus (small *) Note the lateral deviation of the lateral dural reflection of the cavernous sinus (curved arrow) The mass abuts the cavernous internal carotid artery (straight arrow). .

.

. Rhabdomyosarcoma Rhabdornyosarcoma, the most common softtissue sarcoma in children, represents 5%i 5% of all malignant solid tumors in children younger than 1 5 years (i 0) Seventy percent of patients are younger than 1 0 years at pre. sentation, while the peak prevalence is in children aged 2-5 years. The head and neck are the most common sites of origin, with approximately one-third of the tumors involving the nasopharyngeal musculature (22) Local recurrence and distant spread are hallmarks of this disease. Skull base invasion, seen in as many as 35% of patients, usually involves the cavernous sinus and is associated with cranial nerve palsies. Ninety percent of patients eventually die of this complication. Lymph node involvement occurs in one-half of patients, and the lungs and bones are also common sites of metastases. The 5-year survival rate is a disma! 12.5% (10). .

.

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. -

Figure 19. Metastatic disease in a 57-year-old woman with a history of breast carcinoma. Axial CT scan demonstrates a destructive lesion involving the central skull base (arrow).

Volume

10

Number

5

These

gea!

lesions

masses

appear

as bulky

on MR images,

nasopharyn-

commonly

cx-

tending through the skull base to involve the cavernous sinus. The signal intensity is inter mediate between that of muscle and fat on Ti -weighted images. While small areas of bone destruction are difficult to perceive on

MR images

compared

extension into ly appreciated (Fig 18).

with

. Metastatic Disease Metastatic lesions of the occur mon

infrequently than

often gland,

but

primary

occur lung,

CT scans,

tumor

the cranial vault is more on the coronal MR image

central

still

bone

easi-

skull

base

are more

corn-

lesions.

They

most

from carcinoma of the prostate or breast. Prostate gland metas-

tases typically produce hyperostosis associated soft-tissue mass, which mistaken for a meningioma. Lung metastases are generally lytic and

have

a soft-tissue

b!astic onstrate

The

bone

components ofCT (Fig

.

with an may be and breast may also (23) Lytic and generally dem-

component

metastatic enhancement

lesions

destruction

and

are best 19).

Perineural

.

will at CT.

the soft-tissue

evaluated

Tumor

with

the

use

Spread

Perineural and transcranial spread of head and neck malignant neoplasms via the cranial nerves is an important yet underemphasized

mode

of disease

transmission.

While

epithe-

ha! tumors generally exhibit a propensity for this mode of spread, squamous cell carcinoma and adenoid cystic carcinoma are most commonly implicated (24).

Perineural

tumor

involvement

Although any cranial nerve may be involved, most cases described in the literature are confined to the fifth and seventh nerves. Before MR imaging, the primary radiologic finding indicative of this manner of spread was bone erosion of basal foramina, which is evaluated best with CT. With the advent of MR imaging, this form of metastasis can be detected at an earlier stage. Ti -weighted MR imaging can reveal the intraand extracranial extent of perineum! spread. Smooth, isointense thickening of the nerve, associated with concentric enlargement of the foramen, is direct evidence of perineural and transcranial tumor spread (Fig 20) (24).

usually

in-

I INFECTION AND INFLAMMATION Infection involving the skull base most frequent!y results from direct extension of paranasal sinus or mastoid disease but may also develop as a complication of trauma. With extensive disease, an intracranial component may cause meningitis or subdural ernpyema (23) This may occur by direct extension or spread across the multiple foramina and fissures. Three percent of brain abscesses originate from the nasal cavity and paranasal sinuses. Diabetic and immunosuppressed patients are at high risk for the development of extensive infections. Fungal disease is a primary concern in these patients, particularly mucormycosis in diabetic patients (Fig 2 1) and aspergillosis in the immunosuppressed patient (Fig 22) These lesions spread by invasion through the walls of blood vessels, resulting in a purulent arteritis and a high mortalky rate due to rapid intracranial dissemination (23). .

.

dicates a poor prognosis. While most of these patients have advanced disease, the majority may be candidates for some form of surgical

therapy. infiltration

September

Preoperative will

1990

guide

knowledge the

of neural

treatment.

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a. Figure V3. (a)

20. Adenoid cystic Coronal Ti-weighted

carcinoma MR image

of the shows isointense enlargement of the nerve as it enters row) Denervation atrophy and fatty infiltration ment of the motor portion of cranial nerve V3 a! Ti -weighted MR image through the parotid carcinoma within the right parotid gland (*) masseter (curved arrow) and lateral pterygoid .

.

b. parotid gland with perineural spread involving cranial nerve infiltration ofcranial nerve V3 by tumor (*), manifested by the skull base through a widened foramen ovale (large axof the pterygoid muscles (small arrows) , due to involvesupplying the muscles of mastication, is easily seen. (b) Axiregion reveals the primary location of the adenoid cystic Note the denervation atrophy of the muscles of mastication: (straight arrow) muscles.

a. b. Figure 21. Biopsy-proved mucormycosis in a 33-year-old diabetic man with facial pain. (a) Corona! CT scan photographed with bone window shows lesion of nasopharynx with destruction of left pterygoid plate (large arrow) and base of the sphenoid body (small arrow), with extension into a sphenoid air cell. Primary lesion originated in the maxillary sinus (not shown) (b) Axial CT scan shows an enhancing softtissue mass along the greater sphenoid wing (arrow) , representing extension of infection into the middle cranial fossa from the superior orbital fissure. .

816

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et al

Volume

10

Number

5

le 22. Biopsy-proved Id black woman with

aspergillosis right-sided

in a 23facial pain.

a) and coronal (b, c) non-contrast-enId CT scans show a large soft-tissue mass xtensive

I_f

destruction

.-----

of the right (n), ptei-ygoid

(*) maxplate

sinus (m), nasopharynx nd sphenoid sinus (s) The iion may represent calcium

central high atdeposits in my-

ta. Ti-weighted

obtained

:

,

:

bone

.

MR images

before

!id after (e) administration of gadopentetate lumine show the extent of skull base and siivolvement. The central low-signal-intensity kithin the sinus may represent inspissated

.

-

ons

or fungal

mycetoma

containing

metals.

a.

September

1990

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a.

b.

Figure 23. Biopsy-proved central nervous system sarcoid tumor sarcoidosis. Ti-weighted coronal MR images obtained before (a) tetate dimeglumine show an enhancing inflammatory mass (large and cavernous sinus, extending through the foramen ovale along b). Meningeal involvement is also seen (small arrow in b).

in a 32-year-old

woman

with

a history

of

and after (b) administration of gadopenarrow) in the left middle cranial fossa the mandibular nerve (curved arrow in

Due to its propensity for leptomeningeal invasion, sinus and nasopharyngeal sarcoidosis is recognized as a more common cause of cranial nerve neuropathy. Central nervous system involvement occurs in 3%-8% of patients with sarcoidosis. The most frequent problem is cranial neuropathy secondary to facial, acoustic, optic, or trigeminal nerve involvement (Fig 23) (25) Sarcoidosis should be considered when both the meninges and .

the cranial

nerves

are involved

in a patholog-

ic process (25). Axial and coronal CT or MR imaging are methods for detecting early changes to establish biopsy sites and facilitate early diagnosis. CT can also aid in delineation of bone in-

volvement

with

imaging termining

provides extension

osteomyelitis. an accurate through

Coronal method neural

MR for deforamina. -

--#{149}-

B 24.

the skull base bone thickening

818

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Paget

disease.

Axial

CT scan

in an elderly man shows and ‘fluffy’ sclerosis.

‘

‘

Volume

10

through

the typical

Number

5

a. Figure

25.

sided

Polyostotic

blindness.

fibrous

Axial

(a)

and

dysplasia coronal

in a 9-year-old (b)

CT scans

show

b. girl with the

progressive

sclerotic

type

facial of fibrous

deformity

and left-

dysplasia

involving

the central skull base, ca!varia, mandible, and other facial bones. The widened diploic spaces (* in b) and osseous expansion associated with hazy sclerosis are typical. Encroachment of the orbital apex (arrow in a) is easily seen, as are narrowing and encroachment of the superior orbital fissures (arrows in b). Involved bone is seen surrounding the optic canals (arrowheads in b).

I

MISCELLANEOUS

.

Paget

Paget gin,

Disease

disease,

a condition

is seen

primarily

involvement

occurs

with Paget presentation

ease,

to dense

Sclerosis

the base ulate (Fig

.

in

disease ranges

cumscnipta cnanii, bone destruction

most

appearance

Fibrous

continuum

of

osteoporosis

a radiolucent representative

of the skull

the 24).

The

.

on-

adults. Skull of patients

29%-65%

(26) from

sclerosis

is the

of unknown

in olden

cm-

phase with of active dis-

in the common

healing

phase.

finding

when

is involved

and

of fibrous

can sim-

dysplasia

Dysplasla

Fibrous dysplasia, a developmental anomaly of the mesenchymal precursor of bone, manifests itself as a defect in osteoblastic differentiation and maturation (27) Seventy to .

eighty percent of cases are monostotic. While calvarial involvement is usually monostotic,

the

are commonly

skull

involved

form. Up to 50% fibrous dysplasia

September

1990

base

and

facial

volvement, while i 0%-25% of patients with the monostotic form exhibit involvement of these areas (28). The sphenoid, frontal, maxil!ary, and ethmoid bones are most commonly involved, followed by the occipital and temporal bones (28). Patients may present with crania! asymmetry and facial deformity. Fibrous dysp!astic involvement of the optic canal and sphenoid wing may encroach on the optic nerve and lead to blindness. Symptoms and signs referable to the orbit include exophthalmos and visual impairment. Three radiologic appearances of fibrous dysplasia of the skull have been described: (a) pagetoid, (b) sclerotic, and (c) cystic. The sclerotic type most commonly involves the skull base and sphenoid bone (28) Wid.

ened

diploic

spaces

and

osseous

expansion,

along with hazy sclerotic lesions, are cornmon findings. The foraminal encroachment of the skull base caused by the disease is readily seen on CT scans (Fig 25).

bones

in the polyostotic

of patients have skull

with polyostotic and facial in-

Lame

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including treatment,

presence

dose, type of therapy, specific bone involved,

of concurrent

time since and the

trauma

and

infection

(29) Changes usually occur 1 year after treatment and are slowly progressive. Findings include areas of lysis and mixed sclenosis that are most prevalent where the epicen.

ten of the beam tity

is best

was placed

investigated

(Fig

with

26).

axial

This

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2.

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James HE. Encephalocele, dermoid sinus, and arachnoid cyst. In: Mclaurin RI, Venes JL, Schut L, Epstein F, eds. Pediatric neurosurgery. 2nd ed. Philadelphia: 1989; 97-105. PollockJA, Newton Th, Hoyt

Saunders, WF.

Trans.

phenoidal and transethmoidal encephaloceles: a review of clinical and roentgen tures in eight cases. Radiology i968;

Figure

26. CT scan of a 62-year-old woman 5 years after undergoing skull base irradiation for nasopharyngeal carcinoma. CT scan obtained with use of a wide window shows a pattern of mixed sclerosis associated with slight bone thickening, findings

consistent

with

radiation

necrosis

teitis. Differentiation from a chronic as that seen with chronic osteomyelitis,

or os-

osteitis, such would be

en-

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3.

90:442-453. Nager GT. Cepha!oceles. 1987; 97:77-84.

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#{149} Radiation Necrosis The osseous changes of radiation necrosis are thought to be secondary to osteoblastic destruction, followed by vascular damage. The changes seen depend on a variety of factors,

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Drayer BP, Wilkins RH, Boehnke M, Horton JA, Rosenbaum AE. Cerebrospinal fluid rhinorrhea demonstrated by metrizamide CT

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BatsakisJG. Vasoformative mors of the head and neck:

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Whalen MA, Reede DL, Meisler W, Bergeron RT. CT of the base of the skull. Radiol Clin

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ME, Gulati AN, Lame FJ. of the day: CNS sarcoidosis. Graphics i988; 8:578-584. Olmsted

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skeletogenic

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with common calvarial manifestations. diolClinNorthAm i981; 19:703-713. Batsakis JG Non-odontogenic tumors jaws. In: Tumors ofthe head and neck: cal and pathologic considerations. 2nd Baltimore: Williams & Wilkins, 1979; .

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Daffner

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ton DK. Computed tomography of fibrous dysplasia. AJR 1982; i39:943-948. Shimanovskaya K, Shiman A. Radiation injuryof bone. New York: Pergamon, i983; 5783.

RH, Kirks

DR, GehwailerJAJr,

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NewYork: McGraw-Hill, 1985; 834-842. Pritchard DJ, Lunke RJ, Taylor WF, Dahlin DC, Medley BE. Chondrosarcoma: a clinicopathologic and statistical analysis. Cancer 1980;

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Kovacs K, Horvath E, Asa SL. Classification and pathology of pituitary tumors. In: Wi!kins

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more: Williams & Wilkins, i989; 820-821. Oot RF, Melville GE, New PF3. The role of MR and CT in evaluating diva! chordomas and chondrosarcomas. AJNR 1988; 9:7 15Sze G, Uichanco

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Batsakis JG. Soft tissue tumors of the head and neck: unusual forms. In: Tumors of the head and neck: clinical and pathologic con2nd ed. Baltimore: 1979; 350-354.

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Malogolowkin MH, OrtegaJA. sarcoma of childhood. Pediatr

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Ojemann RG. Meningiomas: clinical features and surgical management. In: Wilkins RH, Rengachary 55, eds. Neurosurgery. New York: McGraw-Hill, 1985; 635-654. Batsakis JG Other neuroectodermal tumors and related lesions of the head and neck. In: Tumors of the head and neck: clinical and pathologic considerations. 2nd ed. Baltimore: Williams & Wilkins, 1979; 3 34-349. Mabrey RE. Chordoma: a study of 150

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P. Craniofacial chondrofindings in 15 untreated 10:165-170.

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