12 -Brain Tumors and Tumorlike MASSES .

Brain Tumors and Tumorlike Masses: Classification and Differential Diagnosis with Wolfgang Rauschning Classification by Histology Primary Brain Tumors Metastatic Brain Tumors Classifi

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Brain Tumors and Tumorlike Masses: Classification and Differential Diagnosis

with

Wolfgang Rauschning

Classification by Histology

Primary Brain Tumors

Metastatic Brain Tumors

Classification by Age and General Location

Primary Brain Tumors in Children

Adult Primary Brain Tumors

Classification and Differential Diagnosis by Specific

Anatomic Area

Pineal Region Masses

Intraventricular Masses

Cerebellopontine Angle Masses

Foramen Magnum Masses

Sellar/Suprasellar Masses

Skull Base and Cavernous Sinus Masses

Scalp, (Cranial Vault, and Masses

The crude incidence rate of brain tumors in the

United States is estimated at 4.5 persons per

100,000 population Brain neoplasms are found in

approximately 2% of autopsy series and account for

1% of all hospital admissions.1 Therefore

understanding the classification, pathology, imaging

appearance, and differential diagnosis of brain

tumors by anatomic location is an essential

component of modern neuroimaging

Brain tumefactions comprise a remarkably diverse

group of neoplastic and nonneoplastic conditions that occur at any age and in virtually every location.2 Brain tumors can be any of the following:

1 Primary neoplasms derived from normal cellu-

lar constituents

2 Primary neoplasms that arise from embryolog-

ically misplaced tissues

3 Secondary neoplasms from extracranial primary

sites that metastasize to the CNS

4 Nonneoplastic conditions that can mimic tu-

mors

Any classification system that addresses this multitude of entities is prone to complexity, redundancy, and controversy.2 As the eminent neuropathologist Lucy B Rorke has wryly noted, "Pathologists are neither genealogists nor prophets!"

Although the value of classifying CNS neoplasms and tumorlike lesions is obvious, the conceptual basis for such

a scheme remains controversial and a source of continual differences among neuropathologists.3 Despite numerous attempts, no universally acceptable general classification system has been devised, and some specific tumors remain unclassifiable (or at least create considerable disagreement among recognized authorities).1

Using clinical and imaging data rather than biopsy

C H A P T E R

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402 PART THREE Brain Tumors and Tumorlike Processes

or autopsy specimens to establish an appropriate

dif-ferential diagnosis is the domain of radiologists We will

address the complex issue of brain tumor classification by

using an approach that combines pathologic and imaging

appearances

First, we consider brain tumors as they are traditionally

classified, i.e., by their histologic characteristics We then

categorize these lesions by age and general location on

imaging studies The normal and pathologic anatomy,

classification, and differential diagnosis of tumors and

nonneoplastic tumorlike processes in seven specific

intracranial locations is then considered These seven

areas are selected for particular attention because their

anatomic complexity and broad pathologic spectrum

present special diagnostic challenges

CLASSIFICATION BY HISTOLOGY

Despite numerous efforts, no universally acceptable

pathologic classification of brain tumors has been

proposed Traditionally, the putative histogenetic, or "

cell of origin," approach proposed by Bailey and Cushing

has been the most widely used, although its many

shortcomings have long been recognized.3 The

classification system subsequently developed by Russell

and Rubinstein has been expanded and is in widespread

use.4 More recently, modifications and revisions of the

original World Health Organization (WHO) classification

have been proposed by several authors 1-6a

We will use a modification of the 1993 WHO and

Russell and Rubinstein classifications (see box) and begin

by dividing brain tumors into primary and metastatic

lesions

Primary Brain Tumors

The term primary brain tumor encompasses neoplasms

and related mass lesions that arise from the brain and its

linings Nonneoplastic intracranial cysts and tumorlike

lesions are also included, with pituitary tumors and local

extensions from regional tumors (e.g., craniopharyngioma

and chordoma) that 6 arise from adjacent structures such

as the skull base.6

Primary neoplasms account for approximately two

thirds of all brain tumors (Fig 12-1, A) Primary brain

tumors are subdivided into two basic groups: (1) tumors

of neuroglial origin (so-called gliomas) and (2) nonglial

tumors that are specified by a combination of putative cell

origin and specific location.1 Some pathologists include

all so-called neuroectodermal tumors (neoplasms that

theoretically arise from the embryonic medullary

epithelium) in a single large category that includes both

gliomas and nonglial neoplasms such as primitive

neuroectodermal tumors.6 Because the latter approach is

somewhat unwieldy,

Brain Tumors

Histologic classification

Primary brain tumors

Glial tumors (gliomas)

Astrocytomas Fibrillary astrocytomas Benign astrocytoma Anaplastic astrocytoma Glioblastoma multiforme Pilocytic astrocytoma Pleomorphic xanthoastrocytoma Subependymal giant cell astrocytoma Oligodendroglioma

Ependymal tumors Ependymoma (cellular, papillary) Anaplastic (malignant) ependymoma Myxopapillary ependymoma

Subependymoma Choroid plexus tumors Choroid plexus papilloma

Choroid plexus carcinoma Choroid plexus xanthogranulomas

Nonglial tumors

Neuronal and mixed neuronal-glial tumors Ganglioglioma

Gangliocytoma Lhermitte-Duclos disease Dysembryoplastic neuroepithelial tumors (DNETs) Central neurocytoma

Olfactory neuroblastoma (esthesioneuroblastoma) Meningeal and mesenchymal tumors

Meningioma Osteocartilagenous tumors Fibrous histiocytoma Malignant mesenchymal tumors (e.g., rhabdomyosarcoma)

Hemangiopericytoma Hemangioblastoma Pineal region tumors Germ cell tumors Germinoma Embryonal carcinoma Yolk sac (endodermal sinus) tumors Choriocarcinoma

Teratoma Mixed tumors

we will use the system that divides primary brain tumors into glial and nonglial neoplasms

Neuroglial tumors (gliomas) These tumors are the

largest group of primary CNS neoplasms (Fig 12-1, B) Gliomas are named for their supposed ce1l of origin (see box) The three most common gliomas are astrocytoma, oligodendroglioma, and ependy-

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Chapter 12 Brain Tumors and Tumorlike Masses: Classification and Differential Diagnosis

403

Brain Tumors, cont'd

Histologic classification

Pineal region tumors, cont'd

Pineal cell tumors

Primitive neuroectodermal tumors (PNET)

Medulloblastoma (posterior fossa PNET or

PNET-MB)

Cerebral/spinal PNET

Cranial and spinal nerve tumors

Schwannoma ("neurinoma" or "neurilemoma")

Cysts and tumorlike lesions

Rathke cleft cyst

moma Because the choroid epithelium is derived from

modified ependymal cells, some authors include

choroid plexus papillomas and carcinomas within the

neuroglial tumors.1 A so-called mixed glioma that

contains two or more different cell types also occurs

Astrocytomas Astrocytic neoplasms are subdivided

into several different types (see Chapter 13)

Fibrillary (diffuse) astrocytomas range from the rare

low-grade "benign" astrocytoma to the more common anaplastic astrocytoma and glioblastoma multiforme Fibrillary astrocytomas are primarily supratentorial neoplasms

Pilocytic (hair-like) astrocytomas occur primarily

in childhood and adolescence These tumors are ally-but not invariably-slow growing and occur predominately in the hypothalamus and visual path-ways, brainstem, and cerebellum

gener-Less common astrocytoma subtypes are

pleomor-phic xanthoastrocytoma, and subependymal giant cell astrocytoma (see Chapter 13) The rare "protoplasmic"

and "gemistocytic" astrocytomas are included with anaplastic astrocytoma (see subsequent discussion)

Oligodendroglioma These tumors arise from

oli-godendrocytes and occur mainly in middle-aged adults They are primarily supratentorial masses and occur mostly in the cerebral hemispheres Cortical in-

volvement is common Oligodendrogliomas are

usually relatively well defined and slow growing, although a more malignant anaplastic variety is occasionally encountered

So-called mixed gliomas are relatively rare tumors and histologically heterogeneous neoplasms that con-sist of at least two different glial cell lines The most

common mixed glioma is an oligoastrocytoma

Occa-sionally, ependymal elements are also present Patients with mixed tumors have a slightly better prognosis than those with tumors of pure astrocytic lineage.7

Ependymal tumors Several different cell types

have been described The most common variety,

cel-lular ependymoma, is predominately an infratentorial

tumor that occurs mainly in children and adolescents

It typically fills the fourth ventricle and extrudes through natural passageways such as the lateral re-cesses and foramen of Magendie into the adjacent CSF cisterns

Myxopapillary ependymomas occur exclusively in

the spinal cord and are typically found in the conus

medullaris or filum terminale (see Chapter 21)

Subependymomas are small nodular or lobulated

tumors that are located at the caudal fourth ventricle or foramen of Monro Most occur in middle-aged patients and are usually discovered incidentally or at autopsy

Choroid plexus tumors These uncommon tumors

consist of choroid plexus papilloma (CPP) and

choroid plexus carcinoma Over 90% of primary

choroid plexus tumors are papillomas; carcinomas are very rare CPPs typically affect children under the age

of 5 years Most are found in the atrium of the lateral ventricle Fourth ventricular CPPs are more common

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Fig 12-1 Graphic depiction of brain tumors and their relative incidence A, Primary

neoplasms account for approximately two thirds of all brain tumors; metastases from

extracranial primary malignancies account for the remainder B, Incidence of common

primary brain tumors Gliomas are the largest single group of primary brain tumors, and astrocytomas are the most frequently encountered glioma High-grade astrocytomas (anaplastic astrocytoma and glioblastorna multiforme) are the most common of all primary cerebral neoplasms

Neuronal and mixed neuronal-glial tumors In

adults, glial tumors outnumber neuronal neoplasms by

approximately 100:1.8 Neuronal and mixed

neuronal-glial tumors include gangliocytoma and

ganglioglioma, Lhermitte-Duclos disease,

dysembryoplastic neuroepithelial tumors (DNETs),

central neurocytoma, and olfactory neuroblastoma

(esthesioneuroblastoma) (see Chapter 14)

Tumors of the mesenchyme and meninges Most

primary intracranial mesenchymal tumors arise from

meningothelial cells Meningiomas are the most

com-mon of these mesenchymal neoplasms (see Chapter

14) and the second most common primary CNS neo-

plasm after glioblastoma multiforme gothelial tumors are rare

Meningioma Meningiomas are typically,

well-circumscribed slow-growing tumors that arise from meningothelial arachnoid cap cells More than 90 of meningiomas are supratentorial and occur in certain specific locations, typically around arachnoid villi With the general exception of children who have neurofibromatosis type 2 (NF-2), meningiornas are usually tumors of adults

Miscellaneous mesenchymal tumors These

mes-enchymal, non-meningothelial tumors include benign

neoplasms such as osteocartilagenous tumors and

fibrous histiocytoma Malignant mesenchymal, neo-

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Chapter 12 Brain Tumors and Tumorlike Masses: Classification and Differential Diagnosis 405

plasms are chondrosarcoma, rhabdomyosarcoma, and

meningeal sarcomatosis, among others A combined

glial-mesenchymal tumor, gliosarcoma, is usually

classified with malignant astrocytomas

Hemangiopericytoma is a mesenchymal tumor that

was formerly classified as angioblastic meningioma

There is increasing evidence that these tumors arise

from modified smooth muscle cells and not

menin-gothelial cells (see Chapter 14) Some authors include

hemangioblastoma with meningeal and mesenchymal

hemangiopericytoma as tumors of blood vessel origin

Pineal region tumors A regional approach to

tu-mors of the pineal region is justified by the common

symptomatology and distinctive histologic appearance

of these tumors.2 Pineal region tumors include germ

cell tumors, pineal cell tumors, and other cell tumors

Germ cell tumors Most primary pineal tumors

originate from displaced embryonic tissue.2 The most

common intracranial germ cell tumor is germinoma,

and the typical germinoma location is in the pineal

gland Less common germ cell neoplasms include

embryonal carcinoma, yolk sac (endodermal sinus)

tumors, choroicarcinoma, teratoma, and mixed

tu-mors

Pineal cell tumors Tumors that arise from the

pi-neal gland parenchyma are much less common than

germ cell tumors The two major pineal parenchymal

tumors are pineoblastoma and pineocytoma

Pineoblastomas usually occur within the first three

decades of life These tumors are composed of

prim-itive cells that are histologically similar to

medullo-blastoma (primitive neuroectodermal tumor) and

ret-inoblastoma Pineoblastomas disseminate within the

cerebrospinal fluid (CSF) pathways

In contrast to pineoblastoma, pineocytomas occur

mostly in adolescents and adults The distinction

be-tween pineocytoma and normal pineal parenchyma or

a benign pineal cyst is sometimes difficult on both

imaging and pathologic studies

Other cell tumors A spectrum of other neoplasms

and nonneoplastic masses are found in the pineal

re-gion Examples are benign pineal cysts, astrocytoma

(usually in the tectum, although sometimes primary

pineal gliomas do occur) and meningioma (see

subse-quent discussion)

Embryonal tumors These primitive tumors

in-clude neuroblastoma, ependymoblastorna, and

prim-itive neuroectodermal tumors (PNET) PNETs are

multipotential neoplasms They can differentiate along

neuronal, astrocytic, ependymal, melanotic, or

miscellaneous cell lines The WHO recognizes two

subtypes of PNET: medulloblastoma (posterior fossa

PNET or PNET-ME) and cerebral or spinal PNETs

Cranial and spinal nerve tumors Three types of

nerve sheath tumors occur, as follows:

1 Schwannoma (neurinoma or neurilemoma)

2 Neurofibroma

3 Malignant peripheral nerve sheath tumor

Schwannoma Intracranial schwannomas constitute

5% to 10% of all intracranial tumors and occur primarily in middle-aged adults.1 They show a definite predilection for sensory nerves; the vestibular division

of CN VIII is by far the most common site, followed

schwannomas occur in NF-2 (see Chapter 5)

Neurofibroma Neurofibromas do not arise from

intracranial nerves They are found along posterior ganglia as central extensions of more peripheral tu-mors.1 Exiting spinal nerves and nerve plexuses are common sites The plexiform type of neurofibroma is part of the NF-1 spectrum (von Recklinghausen neu-rofibromatosis) (see Chapter 5)

Malignant peripheral nerve sheath tumor (MPNSTs) MPNSTs arise de novo or from de-

generation of neurofibromas Malignant mation of schwannoma is extremely rare, although

Hemopoetic neoplasms Hemopoetic neoplasms

include malignant lymphomja, leukemia (granulocytic sarcoma), and plasmacytoma

Lymphoma Primary cerebral lymphoma accounts

for approximately 50% of intracranial malignant lymphomas Once considered uncommon, the incidence of primary CNS lymphoma is rapidly rising with the worldwide increase in immunocompromised patients

Leukemia CNS leukemic infiltrates or so-called

granulocytic sarcomas are almost always secondary to

systemic acute myelogenous leukemia A discrete mefaction or granulocytic sarcoma sometimes occurs, usually in the subdural space or infundibular region The greenish hue of this disorder gives rise to the

tu-descriptive term chloroma.2

Plasmacytoma Disseminated vertebral and

epi-dural tumor is the most common CNS manifestation of

multiple myeloma Solitary plasmacytomas are

un-common, although diffuse skull involvement occurs in

up to 70% of patients with disseminated multiple myelomatosis.1 Focal dural masses are occasionally observed Cerebral parenchymal and spinal cord le-sions are rare

Pituitary tumors Tumors of the anterior pituitary

gland, or adenohypophysis, are technically not brain

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tumors They are considered in detail in Chapter 15

The differential diagnosis of sellar and parasellar

masses is considered next

Cysts and tumorlike lesions These cysts and

tu-morlike masses include a spectrum of largely

unre-lated lesions that are all grouped together (see box, p

403), This broad category includes Rathke's cleft cyst,

dermoid and epidermoid cysts, colloid cysts,

enterog-enous and neuroglial cysts, lipomas, and

hamartomas These lesions are discussed in Chapter

15

Local extensions from regional tumors Also

discussed in Chapter 15, this group of lesions

in-cludes neoplasms that extend intracranially from

adjacent structures in or near the skull base

Cranio-pharyngioma, paraganglioma, and chordoma are

examples

Metastatic Tumors

These neoplasms arise from sources outside the

CNS and account for approximately one third of all

brain tumors (see Fig 12-1, A) CNS metastatic

dis-ease has numerous different manifestations and is

considered in detail in Chapter 15

CLASSIFICATION BY AGE AND GENERAL

LOCATION

Between 15% to 20% of all intracranial tumors

oc-cur in children under 15 years of age.4 CNS tumors

are second only to lymphoreticular malignancies in

frequency of childhood cancers and account for 15%

of all neoplasms occurring in this age group.9 Because

the histologic spectrum and general locations of

pri-mary brain tumors are quite different in children

compared to adults, it is useful to consider these two

age groups separately

Primary Brain Tumors in Children

Incidence The incidence of brain tumors in

chil-dren is approximately 2.5 per 100,000 per year.10

Most pediatric brain tumors are primary neoplasms;

CNS metastases are rare in children

Age and presentation Primary brain tumors are

more common in the first decade than in the second;

the peak occurrence is between 4 and 8 years of age.9

Neoplasms in children under 2 years of age are

un-common These are considered congenital tumors and

represent a distinctly different histologic spectrum

compared to older children

Brain tumors in neonates and infants (see box,

above) Only 1% to 2% of all brain tumors occur in

children under 2 years of age.11 Tumors of neonates

and infants have a different topographic and patho-

Brain Tumors In Children Less Than

Two Years of Age Etiology

Teratoma Choroid plexus papilloma

logic distribution compared to those found in older children.12 Tumors in very young children are often large and highly malignant Two thirds occur in the supratentorial compartment Obstruction of CSF pathways with hydrocephalus, split sutures, and macrocrania are common first signs.9

Common brain tumors in children under 2 years of

age are primitive neuroectodermal tumor (PNET or

"peanut" tumor), teratoma, astrocytoma (often anaplastic astrocytoma or glioblastoma multiforme),

and choroid plexus papilloma Teratoma is the most

common intracranial tumor in the neonatal period.13 Less common neoplasms in this age group include

angiosarcoma, malignant rhabdoid tumor, medulloepithelioma, and meningioma.11,14,15 Regardless

of histology, the dominant imaging appearance is that of

a large heterogeneous lesion with associated hydrocephalus Overall prognosis is poor.11

Brain tumors in older children (see box, right)

Approximately half of all intracranial neoplasms in children are gliomas; 15% are PNETs (including medulloblastoma) Ependymoma and craniopharyn-gioma account for about 10% each, whereas pineal re-gion neoplasms cause 3% of tumors in this ago group.9

General location and histology Slightly more

primary intracranial neoplasms in children are supratentorial (52%) compared to infratentorial (48%) in location9; the proportion of supra- to infratentorial lesions varies significantly with age (Fig 12-2)

Supratentorial neoplasms Slightly less than half of all

supratentorial childhood neoplasms are as cytomas; most

are pilocytic or low-grade astrocytomas, and the

opticochiasmatic-hypothalamic area is the

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Fig 12-2 Relative incidence of supra- and infratentorial primary brain tumors in children related to age Supratentorial neoplasms are more common in neonates and young children, and posterior fossa tumors are more common in older children

Data from Harwood-Nash DC: Primary neoplasms

of the central nervous system in children, Cancer

67:1223-1228, 1991

most common location Craniopharyngiomas

represent another one eighth of supratentorial neoplasms in children.9 Ganglioglioma, ependymoma, oligodendroglioma, meningioma, and miscellaneous

other uncommon tumors account for the remainder.16 Metastases from extracerebral primary sites are uncommon in children

Infratentorial neoplasms About one third of

pos-terior fossa neoplasms in children are cerebellar

astrocytomas, and one third to one quarter are PNET/medulloblastomas Brainstem glioma

represents another one fourth, whereas one eighth of pediatric infratentorial neoplasms are

ependymomas.9,17 Other posterior fossa tumors such

as choroid plexus papilloma are unusual in children Most cerebellar astrocytomas are pilocytic astrocy-tomas; intrinsic pontine gliomas are infiltrative, and all are malignant regardless of their histology at the time of biopsy.18 Medullary gliomas behave more benignly.18-20

More than 90% of medulloblastornas (posterior fossa PNET) arise in the vermis Occasionally, medul-loblastomas occur off-axis; about 7% are found in the

cerebellar hemispheres.21

Adult Primary Brain Tumors Incidence Approximately 80% to 85% of all

intracranial tumors occur in adults.22 Most occur in

the supratentorial compartment (see box, p 408)

Adult primary infratentorial tumors are uncommon; most are

extraaxial lesions.23

Age and clinical presentation The peak

incidence of gliomas, the most common group of adult primary brain tumors, is in the seventh decade Clinical manifestations include seizure, focal

Brain Tumors in Children

Nausea, vomiting (posterior fossa)

Focal neurological deficit (e.g., visual

abnormalities with chiasmatic glioma)

Age

Occurrence in first decade more common than in

second decade

Peak age between 4 and 8 years

Location and histology

52% supratentorial

Just under half are cerebral hemisphere astrocyto-

mas (mostly low grade)

One eighth craniopharyngiomas

One eighth opticochiasmatic-hypothalamic gliomas

Remainder

Pineal region tumors (germinoma, pineal

paren-chymal cell tumors)

PNET

Choroid plexus papilloma

Miscellaneous (ganglioglioma, oligodendrogli-

oma are rare)

48% infratentorial

One third cerebellar astrocytomas

One quarter brainstem gliomas

One quarter medulloblastomas (PNET-MB)

One eighth ependymomas

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eadache, nausea, vomiting, and visual symptoms.22

One to two percent of intracranial tumors present

with strokelike symptoms (see Chapter 11)

General location and histology Primary brain

tu-mors comprise about one half to two thirds of all

in-tracranial tumors in adults, and metastases account

for the remainder

Supratentorial tumors Most primary brain tumors

in adults occur above the tentorium.22 Approximately

one half are gliomas About 70% of gliomas are

astrocytomas; more than half of all astrocytomas are

anaplastic astrocytoma or glioblastoma multiforme 1

Increasing age generally correlates with increasing

malignancy

The second most common primary brain tumor in

adults is meningioma, representing 15% to 20% of

these neoplasms More than three quarters of

meningiomas are supratentorial.24

Eight percent most common primary brain tumors

in adults occur in the sellar/parasellar region

Pituitary adenoma is by far the most common

neoplasm in this area

Oligodendrogliomas represent about 5% of all

pri-mary brain tumors Most oligodendrogliomas occur in

adults, and almost all are found in the supratentorial

compartment Other gliomas such as ependy-

moma and CPP occasionally occur in adults They are often

in unusual or atypical locations (e.g., supratentorial or extraaxial ependymoma, or fourth ventricular CPP)

Lymphomas cause 1% to 2% of adult primary CNS

tumors, but their incidence is rising rapidly with the increase in immunocompromised patients

Infratentorial tumors Posterior fossa tumors in adults

are subdivided into intra- and extraaxial processes The three most common primary posterior fossa neoplasms in

adults are all extraaxial: schwannoma, meningioma, and

epidermoid tumors 21

In contrast to children, intraaxial posterior fossa tumors

in adults are rare Hemangioblastoma and brainstem glioma

are the two most common adult primary neoplasms in this

location Metastasis from extracranial primary tumors is by

far the most common intraaxial posterior fossa tumor in adults.21a Fifteen to twenty percent of all intracranial metastases are found in the posterior fossa.21

CLASSIFICATION AND DIFFERENTIAL DIAGNOSIS BY SPECIFIC ANATOMIC LOCATION

The most important factor in establishing an appropriate differential diagnosis for an intracranial mass is location (age is second).25 This section considers the diagnosis of intracranial neoplasms 4 seven specific, anatomic locations These area are listed as follows:

6 Skull base and cavernous sinus

7 Scalp, calvarium, and meninges

In each region, we briefly discuss normal gross imaging anatomy, then review the tumors and nonneoplastic lesions such as vascular malformations and benign cysts that occur

in these specific location Pineal Region Masses Normal anatomy The pineal region is a histologically

heterogeneous area that includes the pineal gland itself, the posterior third ventricle and aqueduct, the subarachnoid cisterns (quadrigeminal plate and ambient cisterns plus the velum interpositum), brain (tectum and brainstem, thalami, corpus callosum splenium), dura (tentorial apex), and vessels (internal cerebral veins and vein of Galen, and posterior choroidal and posterior cerebral arteries) (Fig 12-3}

The pineal gland lies behind the third ventricle, above the posterior commissure, cerebral aqueduct, and tectal plate, and anteriorinferior to the corpus callosum

Brain Tumors in Adults

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409

Fig 12-3 A, Gross anatomy of the pineal region and tectal plate, posterior view The vein of

Galen has been removed B, Midsagittal section through the third ventricle and pineal gland

showing relationships with adjacent structures: 1, Pineal gland 2, Splenium of corpus callosurn 3, Internal cerebral vein 4, Tectum (collicular plate) 5, Vein of Galen 6, Trochlear nerve (CN IV) 7, Velum interpositum 8, Quadrigeminal plate cistern 9, Ambient cistern 10, Posterior choroidal arteries 71, Choroid plexus of third ventricle 12, Cerebral aqueduct 13, Basilar bifurcation with midbrain perforating branches 14, Thalamus (with massa intemedia)

15, Optic chiasm 16, Hypothalamus with infundibular stalk 17, Fornix 18, Foramen of Monro 19, Posterior commissure 20, Basal veins of Rosenthal 21, Posterior cerebral artery

22, Tentorium cerebelli (From Basset DL: A Stereoscopic Atlas of Human Anatomy: the

Central Nervous System, Section 1 Courtesy Bassett Collection, R Chase (curator), Stanford

University.)

Fig 12-4 A, Midsagittal cut brain section and, B, sagittal T2-weighted MR scan

depict the pineal gland and its adjacent structures Same key as Fig 12-3 (Brain section courtesy Yakovlev Collection, Armed Forces Institute of Pathology.)

splenium (Fig 12-4) The suprapineal recess of the

third ventricle extends posteriorly immediately

above the pineal gland The quadrigeminal plate

cistern lies behind the pineal gland An anterior

extension of this cistern, the velum interpositum,

lies above the pineal gland and extends anteriorly

under the fornix

Important vascular, dural, and neural structures are adjacent to the pineal gland The tentorial apex arches above and behind the pineal gland, and the internal cerebral veins and vein of Galen lie in close proximity (Figs 12-4 and 12-5) Branches of the medial and lateral

posterior choroidal arteries are also present (see Fig

6-19) The two CN IVs exit dorsally

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from the midbrain, decussate, and then course

ante-riorly in the ambient cisterns adjacent to the tentorial

incisura

Pathology: overview The list of possible pineal

region masses is extensive and includes germ cell

tu-mors, pineal cell tutu-mors, "other" cell tutu-mors, and

nonneoplastic masses (see box) Together these lesions

represent about 1% to 3% of all intracranial masses

26,27

It is very helpful to subdivide pineal region masses

into more specific locations (Fig 12-6) We first

con-sider lesions that arise within the pineal gland itself,

then discuss posterior third ventricle and

quadrigem-inal cistern masses Adjacent brain parenchyma areas

such as the tectum, midbrain, and corpus callosum

have a different spectrum of abnormalities that may

cause a pineal region mass Finally, we consider

lesions that arise in the pineal region from adjacent

vascular and dural structures

Common Pineal Region Masses Germ cell tumors

Germinoma Teratoma

Pineal parenchymal cell tumors

Pineocytoma Pineoblastoma

Other cell tumors and neoplastic-like masses

Pineal cysts Astrocytoma (thalamus, midbrain, tectum, corpus callosum)

Meningioma Metastases Vascular malformation (with or without enlarged vein of Galen)

Miscellaneous (lipoma, epidermoid, arachnoid cyst)

Pineal gland lesions Pineal region masses account

for 1% to 2% of all brain tumors but constitute 3% to 8% of intracranial tumors in children.4,28-30

Pineal gland neoplasms Pineal tumors are

com-nonly but mistakenly referred to as "pinealomas." The correct terminology of pineal region masses is listed in the box

Common pineal gland tumors are neoplastic derivatives of multipotential embryonic germ cells.27 These tumors account for more than two thirds of all pineal region masses Germ cell tumors have a peak incidence during the second decade.30

Fig 12-5 Axial (A and B) and coronal (C) T2-weighted

MR scans show the pineal region anatomy in detail Same key as Fig 12-3

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411

Fig 12-6 Anatomic diagram depicts the pineal region and its common lesions

The approximate course of the tentorial incisura is shown by the dotted line

Fig 12-7 A 7-year-old boy with acute onset of diabetes insipidus Sagittal T1-weighted MR

scans without (A) and with (B) contrast enhancement show a large uniformly enhancing

pineal region mass (white arrows) The mass depresses the tectal plate (black arrows) The

infundibular recess appears slightly thickened and enhances following contrast

administration (open arrows)

Dilated suprapineal recess

Ependymal /inflammatory cyst

Choroid plexus papilloma

Tectum

Chiari II (beaking) Astrocytoma Multiple sclerosis

Vessels, dura Tortuous vessels Enlarged vein of Galen Meningioma

Tentorial subdural hematoma

Brain

Astrocytoma Vascular malformation Stroke

Demyelinating disease Metastasis

Herniations

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Germinoma is by far the most common of the germ

cell neoplasms (Fig 12-7) (see Chapter 14)

Synchro-nous lesions in the pineal and suprasellar regions

ac-count for 5% to 10% of all intracranial germ cell

tu-mors.31 The second most common germ cell tumor is

teratoma, accounting for approximately 15% of all

pi-neal masses (Fig 12-8).27 Teratomas arise from

mul-tipotential cells that produce tissues representing a

mixture of two or more embryologic layers.27 Terato-

Fig 12-7, contd Coronal postcontrast study (C)

confirms a second lesion in the inferior third ventricle

(arrow) Note hydrocephalus secondary to aqueductal

stenosis Synchronous pineal-suprasellar

germinomas

Fig 12-8 An 8-year-old boy with malignant pineal

teratoma Postcontrast sagittal T1-weighted MR scan

shows a partially enhancing mixed signal pineal

gland mass (arrows)

mas can be benign (typical, or mature or immature) or malignant (formerly called teratocarcinoma)

Less common germ cell tumors include

choriocarci-noma, endodermal sinus (yolk sac) tumor, and enibryonal carcinoma Mixed cell types also occur.32

Tumors that arise from pineal parenchymal cells account for less than 15% of all pineal region neoplasms Unlike germinomas these tumors may be found in patients beyond the second decade of life.27 There are two types of pineal cell neoplasms: pineocytoma and pineoblastoma

Pineocytomas are benign, well-delineated tumors with

mature cells that are histologically-and often radiologically-almost indistinguishable from normal pineal

parenchyma (Fig 12-9) Pineoblastomas are malignant

neoplasms that are composed of undifferentiated or immature pineal cells Pineoblastomas are considered a type of PNET similar to medulloblastoma.27

Pineal parenchymal neoplasms other than pineocytoma

or pineoblastoma are rare Occasionally, metastases or gliomas with ganglionic or astrocytic differentiation are identified.27

Nonneoplastic pineal gland masses Nonneoplastic

pineal cysts are benign cystic lesions that ad lined by

collagenous fibers, glial cells, and normal pineal parenchymal cells.33,34 Theories on the origin of pineal

cysts include degenerative change, coalescence of smaller cysts, sequestration of the pineal diverticulum, and failure

of normal pineal development.35

Small asymptomatic nonneoplastic pineal gland cysts are

common incidental findings, seen in up to

Fig 12-9 A 24-year-old woman with headaches

and normal neurologic examination Axial postcontrast CT scan shows a partially calcified

cystic-appearing pineal gland mass (arrows)

Pineocytoma

Trang 13

40% of routine autopsies (Fig 12-10, A and B) and

1% to 5% of unselected MR scans (Fig 12-10, C to

F).36,37 Occasionally, the imaging appearance of

be-nign pineal cyst is indistinguishable from small

cys-tic pineal neoplasms such as pineocytomas.33 CT or

MR-guided stereotactic biopsy has been recom-

mended for the evaluation and management of symptomatic cases.38

Other than glial cysts, benign pineal masses are uncommon Sarcoidosis has been reported as causing

a focal pineal mass.39

Fig 12-10 Gross pathology of benign pineal cyst incidentally found at autopsy A, View from

below shows the cyst (arrow) compresses and flattens the midbrain B, Midsagittal section shows

the cyst (arrow) and compressed tectal plate Axial T1- (C), proton density (D), and T2-weighted

(E) MR scans without contrast in a 34-year-old woman with headaches disclosed a cystic pineal

mass (arrows) that is slightly hyperintense to CSF on all sequences Sagittal postcontrast T1WI (F)

shows partial rim enhancement (small arrows) The lesion was followed for 3 years and did not

show interval change on serial imaging studies Presumed nonneoplastic benign pineal cyst (A and

B, Courtesy E Tessa Hedley-Whyte.)

Trang 14

Posterior third ventricle lesions

Nonneoplastic masses A markedly dilated

suprapineal recess may occur with longstanding

aqueductal stenosis (Fig 12-11) Occasionally,

ependymal or inflammatory cysts can be found in the

posterior third ventricle Colloid cysts are typically

located more anteriorly

Fig 12-11 Sagittal T1-weighted MR scan in a

patient with long-standing aqueductal stenosis and

severe hydrocephalus shows a massively enlarged

suprapineal recess of the third ventricle (black

arrows) Note flattening and inferior displacement of

the vermis (single white arrows), descending tonsillar

herniation (curved arrow), and "partially empty" sella

(double arrows) caused by inferior herniation of the

anterior third ventricular recesses into the sella

tur-cica

Fig 12-12 Multiple overlapping thin-slab MR

angiogram shows an extremely ectatic, tortuous

basilar artery (large arrow) Vein of Galen is seen

(open arrows)

Fig 12-13 A, Sagittal precontrast T1-weighted MR scan in a 2-year-old child with Parinaud

syndrome shows a large posterior third ventricular mass (large arrows) with severe compression of

the tectum (small arrows) B, Axial postcontrast T1WI shows the mass (arrows) enhances intensely

Choroid plexus papilloma was found at surgery

near the foramen of Monro (see subsequent discussion) The third ventricle can be elevated and extrinsically compressed by an ectatic, elongated basilar artery or basilar bifurcation aneurysm (Fig 12-12)

Neoplasms Masses located entirely within the

posterior third ventricle are rare; most anise from the choroid plexus Meningioma, choroid plexus

papilloma, and metastases are the most common

neoplasms that occur in this location (Fig 12-13) Tumors that involve the posterior third ventricle usually arise from the thalamus or pineal gland and extend into the ventricle secondarily.40

Trang 15

Fig 12-14 Sagittal postcontrast T1-weighted MR

scan shows a tectal plate glioma (arrow)

Neoplasms Tectal gliomas are usually low-grade

astrocytomas that enlarge the tectum (Fig 12-14) The aqueduct may be engulfed and occluded (Fig 12-15), resulting in obstructive hydrocephalus

Lymphoma

occasionally involves the tectum.41

Nonneoplastic masses and miscellaneous lesions

Vascular malformations that involve the tectum

in-clude cavernous angiomas (Fig 12-16, A), pial AVMs, and mesencephalic AVMs with aneurysmal

dilatation of the vein of Galen (Fig 12-16, B)44 (see

Chapter 10) Thalamoperforating artery occlusions

may result in midbrain and tectal infarcts Other

abnormalities of the dorsolateral midbrain include

trauma (Fig 12-17), demyelinating disease, and progressive supranuclear palsy.41

Fig 12-15 Axial (A) and sagittal (B) postcontrast T1-weighted MR scans show an

en-hancing mass in the periaqueductal region (arrows) Presumed glioma (not biopsied)

Tectum The lamina quadrigemina (paired

supe-rior and infesupe-rior colliculi) forms the midbrain roof

Although a diverse group of lesions may affect the

tectum, intrinsic tectal lesions have a comparatively

limited differential diagnosis.41

Normal variations and congenital anomalies

There is little variation in tectal size, although the

in-ferior colliculus may be slightly larger than the

supe-rior colliculus A supesupe-rior colliculus that is larger

than its inferior counterpart is usually abnormal

Most patients with Chiari II malformation have

mesencephalic abnormalities These range from

slight loss of the normal intercollicular groove

through collicular fusion to a markedly elongated

beak-shaped tectum42 (see Chapter 2)

Mesencephalic beaking is seen in nearly 90%.43

Trang 16

Fig 12-16 Two cases illustrate vascular malformations in the pineal region A,

Axial T1-weighted MR scan shows a cavernous angioma (arrows) B, Axial

postcontrast CT scan in a newborn with high-output congestive heart failure shows

an enlarged vein of Galen (arrows) secondary to mesencephalic AVM (not shown)

Quadrigeminal cistern and velum interpositum

Various lesions occur in the subarachnoid spaces that

surround the pineal gland

Normal variations and congenital anomalies A

common normal variation is a cavum velum

interposi-tum (CVI) (Fig 12-18, A) CVI is a

triangular-shaped, CSF-filled anterior extension of

the quadrigeminal plate cistern that lies above the

pineal gland and dorsal third ventricle CVIs and

masses within and above the velum interpositum

(e.g., arachnoid cyst and corpus callosurn gliomas)

typically displace the internal

Fig 12-17 Axial NECT scan in a patient with severe

head trauma Initial CT scan obtained 2 days earlier showed only minor abnormalities Dorsolateral midbrain contusion with hemorrhage in the quadrigeminal cistern and tectum is now apparent

(arrows) (Courtesy Ivan Robinson.)

Chapter 15) Quadrigeminal plate lipomas usually occur in isolation, but up to one third are associated with other congenital anomalies.27

Trang 17

Fig 12-18 A, Axial T1-weighted MR scan shows a cavum velum interpositum

(CVI) (arrows) The pyramidal-shaped CSF collection that lies between the two

lateral ventricles is characteristic B, Sagittal T1-weighted MR scan in another

patient shows an arachnoid cyst within the CVI (large arrows) Note inferior displacement of the pineal gland (double arrows) and elevation of the corpus callosum (open arrows), indicating the mass is located in the CVI

Fig 12-19 A, Gross pathology specimen shows a quadrigeminal plate lipoma (arrow)

found incidentally at autopsy B, Axial T1-weighted MR scan shows an incidental lipoma,

seen as the hyperintense lesion (arrow) (A, Courtesy E Tessa Hedley-Whyte.)

SAH typically involves the pontine and ambient

cisterns but may extend dorsally into the

quadrigemi-nal cistern (see Chapter 7)

Neoplasms Primary neoplasms of the

quadrigem-inal cistern are rare Occasionally, epidermoid or

der-moid tumors occur in this location (Fig 12-22)

Leptomeningeal metastases from numerous primary

brain tumors and extracerebral sources most often affect the basilar CSF subarachnoid spaces, but diffuse tumor

Nonneoplastic masses and miscellaneous lesions

Quadrigeminal cistern arachnoid cysts are congenital

cystic CSF collections located between the tectum

and tentorial incisura (Fig 12-20).46 They repreDent

about 8% of all intracranial arachnoid cysts.47

Occasionally, an arachnoid cyst occurs within the

ve-lum interpositum (Fig 12-18, B) Meningitis and

subarachnoid hemorrhage (SAH) can affect the

quadrigeminal cistem (Fig 12-21) Nonaneurysmal

perimesencephalic

Trang 18

Fig 12-20 A, Gross pathology specimen shows a quadrigeminal arachnoid cyst

(arrows) found incidentally at autopsy B, Axial CECT scan shows a quadrigeminal

arachnoid cyst (arrows), seen as the low-density CSF collection immediately posterior

to the tectum (A Courtesy E Tessa Hedley-Whyte.)

spread can involve the ambient, superior vermian,

and quadrigeminal plate cisterns and even the velum

interpositum (Fig 12-23)

Vascular and dural lesions The most common

vascular mass in the pineal region is an elongated,

tortuous basilar artery that elevates and compresses

the third ventricle Occasionally, aneurysms of the P2

or P3 posterior cerebral artery segments occur here

(Fig 12-24) A choroidal artery fistula or mesence-

Fig 12-21 Striking changes of superficial siderosis

are seen on the axial T2-weighted MR scan of a patient with repeated subarachnoid hemorrhages Note pial hemosiderin staining of all the pineal

region structures (arrows)

phalic AVM with an aneurysmally dilated vein of

Galen is a rare but important vascular lesion that

causes a pineal region mass (Fig 12-16, B) Common tentorial apex masses include

meningioma (Fig 12-25) and subdural hematoma

Brain parenchyma Brain parenchymal structures that lie in close proximity to the pineal gland are the corpus callosum splenium, tectum, posterior commissure, and midbrain Therefore the full spectrum

Trang 19

Fig 12-22 Quadrigeminal and ambient cistern epidermoid tumor is shown in these

studies A, Axial NECT scan shows a very low density, slightly lobulated mass in the

right ambient cistern (arrows) Axial T1- (B), proton density- (C) and T2-weighted (D)

MR scans show the mass (arrows) has the same signal intensity as CSF

Fig 12-24 Lateral vertebral angiogram, arterial

phase, shows a distal posterior cerebral artery

aneurysm (arrows) The patient had systemic fungal

infection

Fig 12-23 Sagittal postcontrast T1-weighted MR

scan in a patient with diffuse leptomeningeal

metastases from breast carcinoma shows extensive

tumor covering nearly all pial surfaces Note thick,

enhancing rind of tumor that covers the

quadrigeminal plate and extends anteriorly into the

velum interpositum (arrows)

Trang 20

Fig 12-25 Two cases of tentorial apex meningioma causing a pineal region mass A, Axial

CECT scan shows a round, uniformly enhancing mass (large arrows) that lies between the tentorial leaves (curved arrows) Note the calcified pineal gland (open arrow) is anterior to

the mass B, A 73-year-old woman with ataxia, gait abnormalities, and urinary incontinence

had a CT scan (not shown) that showed a "pineal tumor." Axial postcontrast T1-weighted

MR scan shows a large intensely enhancing mass (large arrows) at the tentorial apex Note the dural "tail" (curved arrow), Incidentally noted are bilateral choroid plexus cysts

(arrowheads) (A, Courtesy J Jones.)

Fig 12-26 Autopsy-proven multiple sclerosis in this patient is seen as a tectal mass

A, Axial T1WI shows the low signal mass enlarges and distorts the tectum (arrows)

B, The T2-weighted study shows the hyperintense midbrain lesions (arrows)

of brain demyelinating (Fig 12-26) and metabolic

diseases, vascular malformations and infarcts (Fig

12-27), and primary (Fig 12-28) and metastatic

tumors (Fig 12-29) may involve the brain around the

pineal region

Displacement of otherwise normal brain structures

into the quadrigeminal cistern occurs with some brain

herniations Upward herniation of the cerebellar vermis through the tentorial incisura obliterates the quadrigeminal plate cistern and compresses the tectum (Fig 12-30) Descending temporal lobe herniation may cause medial displacement of the hippocampus over the incisura, compressing the midbrain and adjacent ambient cistern

Trang 21

Fig 12-27 Sagittal (A) and axial (B) T1-weighted MR scans in a patient with

"top of the basilar" infarctions secondary to multiple thalamoperforating artery embolic occlusions Note multiple lacunar infarcts in the thalami, hypothalamus,

midbrain, and tectum (arrows)

Fig 12-29 Axial CECT scan shows multiple

thin-walled metastases, some with mural nodules

(black arrows) A midbrain metastasis is indicated (open arrow) Carcinoma of the lung.

Fig 12-28 Axial postcontrast T1-weighted MR

scan in a patient with an extensive cystic midbrain

astrocytoma that involves the tectum (arrows)

Trang 22

Fig 12-30 Sagittal T1-weighted MR scan shows a huge

cystic cerebellar astrocytoma (large arrows) fills most of

the posterior fossa The enlarged vermis herniates upward

through the tentorial incisura, compressing the tectum

(double arrows) Note downward tonsillar displacement

through the foramen magnum (curved arrow)

Intraventricular Masses In Children

Foramen of Monro/third ventricle

Foramen of Monro

Subependymal giant cell astrocytoma Astrocytoma

(N.B.-colloid cysts are rare in children; when they

occur they are usually in older children and adolescents)

Third ventricle

Extrinsic mass (e.g., craniopharyngioma) Astrocytoma (low grade, pilocytic) Histiocytosis (anterior recesses/hypothalamus/infundibular stalk)

Intraventricular Masses

One tenth of all CNS neoplasms involve the

ven-tricles Imaging characteristics are usually

nonspe-cific; exact location of the mass and the patient's age

are the most helpful information in the differential

diagnosis of these lesions (see boxes).49

Lateral ventricles The lateral ventricles are

paired C-shaped structures (Fig 12-31) Each is

subdivided into frontal horn, body, atrium (trigone),

occipital horn, and temporal horn The lateral

ventricles curve around the thalami and diverge from

the midline as they pass posteriorly The superior

surface of each lateral ventricle is formed by the

corpus callosum The caudate nucleus, thalamus, and

hippocampus form the lateral and inferior borders

Half the intraventricular tumors in adults and one

quarter of the intraventricular masses in children are

found in the lateral ventricles.50 The diagnosis of

these lesions varies significantly with age and

location within the ventricle itself (Fig 12-32).25

Frontal horn The frontal horns of the lateral

ven-tricles are separated by the septum pellucidum (Fig

12-33) The septum pellucidum is a thin translucent

triangular membrane that consists of two glial

lami-nae with a potential space (cavum) in between.51 The

septum pellucidum extends anteriorly and superiorly

from the fornix to the corpus callosurn.52

Several congenital anomalies affect the septum

pellucidum and frontal horns An absent septum

pellucidum almost always indicates substantial

neurologic disease (Fig 12-34, A and B).52 The

septum is absent in holoprosencephaly, septooptic

dysplasia, and corpus callosum dysgenesis

Cavum septi pellucidi (CSP) and cavum vergae (CV) are common developmental anomalies that

represet persistence of normal fetal cavities Eighty percent of normal neonates have CSPs; a

CV is seen in 30% of term infants Both CSP and CVs shrink and eventually disappear after birth A persistent CSP is present in 2% to 4% of normal adults51 and is seen on imaging studies as a CSF-filled collection that is contain between the two septal leaves (Fig 12-33, B) A CV appears as

a posterior extension of a CSP CV never occurs without a CSP On imaging studies a seen as a fingerlike CSF collection that lies in the mid-

Trang 23

Fig 12-31 Anatomic diagram depicts the brain ventricular system: Green, Lateral ventricles 1,

Frontal horn 2, Body 3, Atrium 4, Occipital horn 5, Temporal horn Yellow, Foramen of Monro

Blue, Third ventricle with pineal gland (p), massa intermedia (m), suprapineal recess (spr), and

optic (o) and infundibular recesses (i) Orange, Aqueduct Red, Fourth ventricle with fastigium

(f), posterosuperior recesses (psr), and lateral recesses (lr) Foramen of Magendie (curved arrow)

Foramina of Luschka (double arrows)

Intraventricular Masses in Adults

Astrocytoma (anaplastic, glioblastoma) Astrocytoma (anaplastic, glioblastorna)

Cavum septi pellucidi and cavum vergae Third ventricle

Subependymoma

Choroid plexus cysts/xanthogranulomas Aqueduct

Enlarged calcified choroid plexus with NF-2 Metastasis

Hemangioblastoma Exophytic brainstem glioma Subependymoma

Trang 24

Fig 12-32 Anatomic diagram depicts the brain ventricular system and common lesions

encountered in each specific location

Trang 25

Fig 12-33 A, Axial cut brain section through the lateral ventricles and foramen of

Monro B, Axial T2-weighted MR scan through the frontal horns shows foramen of

Monro anatomy: 1, Frontal horns 2, Septum pellucidum 3, Pillars of fornix 4, Internal

cerebral veins 5, Foramen of Monro 6, Choroid plexus 7, Velum interpositum 8,

Cor-pus callosurn genu 9, CorCor-pus callosurn splenium B, A small cavum septi pellucidi (csp)

is shown (A, Courtesy Yakovlev Collection, Armed Forces Institute of Pathology.)

Fig 12-34 Congenital anomalies of the septum pellucidum are illustrated in three cases A,

An 8-year-old child who has had panhypopituitarism since birth Coronal T1-weighted MR

scan shows absent septum pellucidum The frontal horns of the lateral ventricle have a

"squared-off" appearance (large black arrows) The posterior pituitary gland is ectopically

located in the hypothalamus (double arrows), and the infundibular stalk is extremely small

(curved, white arrow) B, A 20-year-old patient with seizures Coronal T1-weighted MR

scan shows absent septum pellucidum, the "nipple" of a schizencephalic cleft (curved arrow)

and heterotopic gray matter (open arrows) Note "squared-off" appearance of the frontal

horns (large black arrow)

Continued.

Trang 26

Fig.12-34, cont'd C and D, Axial T1-weighted MR scans show a cavum septi

pellucidi (csp) and vergae (cv)

fine below the corpus callosum and between the

for-nices (Fig 12-34, C and D)

Primary septa] neoplasms are uncommon in the

absence of a CSP, a septum pellucidum that is thicker

than 3 mm is suspicious for infiltrating neoplasm

The most common primary septal tumor is

astrocy-toma (Fig 12-35) Other neoplasms in this region

in-clude lymphoma (Fig 12-36) and germinoma (Fig

1237) Dysplastic thickening can sometimes be seen

in NF-1

Fig 12-35 Axial T1-weighted MR scan shows a slightly

hy-pointense mass in the septum pellucidum (arrows) Infiltrating

low-grade astrocytoma

Most frontal horn masses actually arise f adjacent structures, i.e., the head of the caudate nucleus, septum pellucidum, or foramen of Monro (see subsequent discussion) Intraventricular extension of anaplastic astrocytoma is an example Other tumors with a strong predilection for the septum pellucidum or frontal horn

include central neuroqcytoma, subependymoma, and

giant cell astrocytoma (Fig 12-38).53

Body In children younger than 5 or 6 years of age

Trang 27

427

Fig 12-36 CNS lymphoma Axial CECT scans show extensive subependymal

enhancing tumor along the lateral ventricular walls and septum pellucidum

(arrows).

Fig 12-37 Axial pre- (A) and postcontrast (B) T1-weighted MR scans show

thickened, enhancing septum pellucidurn (arrows) Germinoma

Fig 12-38 Tumors at the foramen of Monro, septum

pellucidum, and frontal horns are illustrated A,

Coronal gross pathology specimen of incidental

subependymoma found at autopsy (A, Courtesy

Rubenstein Collection, University of Virginia.)

Continued

Trang 28

Fig 12-38, cont'd B, Coronal T1-weighted MR scan in a patient with tuberous sclerosis

shows a mixed iso- and hypointense mass at the foramen of Monro (arrows) ,

Subependymal giant cell astrocytoma C, Axial postcontrast T1-weighted MR scan in

an-other patient with a central neurocytoma (arrows) (C, Courtesy D Baleriaux.)

Fig 12-39 Newborn infant with

large head A, Axial NECT shows a

large hyperdense mass (arrows) that

occupies the body and atrium of the right lateral ventricle Axial

T2-weighted (B) and postcontrast T1WI (C and D) MR scans show a

strongly enhancing mixed sign

(large arrows) that has trapped

temporal and occipital horns Note diffuse ependymal and subarachnoid tumor spread (arrowheads)

Anaplastic astrocytoma with widespread leptomeningeal and ependymal metastases

Trang 29

in this location, although most supratentorial

ependymomas are extraventricular (see Chapter 13) Lateral ventricular masses in older patients are astro-

cytoma (usually higher-grade tumors),

oligodendroglioma, meningioma, lymphoma, metastases, and subependymoma

Atrium Choroid plexus papilloma (CPP) is the

most common trigone mass in young children (Fig

12-40) Ependymomas and astrocytomas occur in older children (Fig 12-41) Meningioma, metastasis

(Fig 12-42), and

Fig 12-40 Axial pre- (A) and postcontrast (B) CT scans in a 1-year-old child with

de-layed development show a large soft tissue mass in the atrium of the left lateral ventricle

A, The mostly isodense mass (large arrows) has some internal calcifications (open

ar-rows) B, The mass (arrows) enhances strongly and uniformly after contrast

administra-tion Some slight surface lobulation is apparent, caused by CSF trapped between the fronds of this classic choroid plexus papilloma

Fig 12-42 Axial CECT scan in a 74-year-old man

with renal carcinoma shows an enhancing mass in the

choroid glomus (arrows) Metastatic carcinoma was

found at surgery

Fig 12-41 Axial T2-weighted MR scan of an

ependymoma in the atrium of the right lateral

ventricle shows a large mixed signal mass (large

arrows) with prominent foci of high-velocity signal

loss (small arrows) caused by tumor vascularity

lateral ventricular masses that are located primarily in

the body include primitive neuroectodermal tumor

(PNET), teratoma, and astrocytoma (usually anaplastic

astrocytoma or glioblastoma multiforme) (Fig 12-39)

In older children and young adults, astrocytoma is the

most common neoplasm in this location

Two tumors that are often found in the lateral

ven-tricle body are central neurocytoma and

oligodendroglioma They are usually seen in patients

between 20 and 40 years of age.53 Ependymomas

occasionally occur

Trang 30

lymphoma are typical lesions in older adults.54

Vascu-lar malformations can be seen at any age.55

Choroid plexus cysts are nonneoplastic

epithelial-lined cysts that usually occur within the glomus (Fig

12-43, A) Most are bilateral and are found

incidentally in neonates and older adults.56,57 Most

appear isointense with CSF on T1-weighted MR scans

but slightly hyperintense on long TR/short TE

sequences (Fig 12-43, B to D) Xanthogranulomas are

benign choroid plexus masses composed of large

foam-filled cells with clusters of lymphocytes and

macrophages They are usually bilateral and typically

occur in older adults Occasionally, they can be seen in

children and may attain strikingly large size 58

Occipital and temporal horns Primary

intraven-tricular masses are very uncommon in the occipital

horn Occasionally, meningiomas occur here (see

Chapter 14) The temporal horn choroid plexus is

sometimes enlarged and calcified in patients with

Fig 12-43 Coronal gross specimen (A) shows bilateral choroid plexus xanthogranulomatous

cysts (arrows), found incidentally at autopsy Axial T1- (B), proton density (C), and T2-weighted

(D) MR scans in another patient show bilateral choroid plexus cysts (arrows) The cysts are

slightly hyperintense to CSF on all sequences (A, From Okazaki H, Scheithauer B: Slide Atlas of

Neuropathology, Gower Medical Publishing, 1988 With permission.)

neurofibromatosis type 2 (Fig 12-44) The temporal and occipital horns may become trapped and encysted

by neoplasms in the atrium or adjacent brain parenchyma (Fig 12-45)

Foramen of Monro and anterior third ventricle

The foramen of Monro (FM) is a Y-shaped g1ructure that connects the two lateral ventricles with the third ventricle (Fig 12-46) The FM is bordered rostrally and anteriorly by the columns of the fornix Its posterolateral margins are demarcated by choroid plexus and confluence of the septal, anterior caudate terminal, and choroidal veins The roof of the anterior third ventricle is formed by the fornix, tela, choroidea, and internal cerebral veins It normally has smooth, upwardly convex configuration 59

FM masses are uncommon in young children

Subependymal giant cell astrocytoma (SGCA) occurs

in older children and young adults with tuberous scle-

Trang 31

431

Fig 12-44 Axial T1-weighted MR scans in a patient with neurofibromatosis

type 2 (NF-2) show enlarged, partially calcified choroid (arrows) in the temporal

horn and atrium of the right lateral ventricle

Fig 12-45 A, Gross autopsy specimen of a glioblastoma multiforme shows a

large, necrotic, hemorrhage mass (large arrows) has trapped the temporal horn

The enlarged temporal horn shows abnormally thickened ependyma (small

arrows) B, Axial CECT shows the tumor mass (large arrows) with ependymal

enhancement (small arrows) around the encysted temporal horn (Courtesy D

Baleriaux and J Flament-Durand.)

Trang 32

Fig 12-46 A, Coronal gross specimen shows the foramen of Monro and adjacent

structures B, Coronal T2-weighted MR scan shows normal foramen of Monro

anatomy: 1, Foramen of Monro 2, Pillars of fornix 3, Septum pellucidum 4, Internal cerebral veins 5, Caudate nuclei 6, Thalami 7, Frontal horns of lateral ventricles 8,

Third ventricle (A, Courtesy Yakovlev Collection, Armed Forces Institute of

Pathology.)

Fig 12-47 A, Sagittal view of gross autopsy

specimen with an incidental colloid cyst (arrow) at

the foramen of Monro B, Sagittal Tl-weighted MR

scan in a patient with headaches shows a focal high

signal mass (arrow) at the foramen of Monro A small

colloid cyst was surgically removed (A, Courtesy E

Tessa Hedley-Whyte.)

rosis Pilocytic astrocytoma also occurs in his age group Subependymoma and central neurocytoma occur in adults (see preceding discussion)

Anterior third ventricle Colloid cysts are the most

common mass in this location (Fig 12-47).59 These sions are common in adults but rare in children Coloid cysts have a variable imaging appearance that depends on their contents (see Chapter 15).60 Turbulent CSF flow can produce a "pseudotumor" in this location (Fig 12-48) Occasionally an extremely gated, ectatic basilar artery or basilar tip aneurysm seen as a foramen of Monro mass (Fig 12-49)

le-Primary third ventricular neoplasms are rare at any

age; most are astrocytomas that arise from the (Fig

12-50), or tela choroidea, of the third ventricle The vast majority of neoplasms that involve the t ventricle originate in adjacent structures and the third ventricle

by direct extension In children craniopharyngioma and hypothalamic astroytoma are the two most common tumors in this location.61 Germinoma may

involve the anterior third ventricular recesses Suprasellar germinomas usually-but not always-occur with a synchronous pineal tumor, (Fig 12-7) and often involve the infundibular stalk as well.31 Ten percent of

choroid plexus papillomas are located within the third

ventricle; almost all occur children under 5 years of age (Fig 12-13)

In adults, third ventricular masses are also usually secondary to extraventricular lesions The third ventricle is often elevated and compressed by suprasel-

Trang 33

Fig 12-48 Coronal postcontrast T1-weighted

MR scan shows a foramen of Monro

pseudomass (large arrow) caused by pulsatile

flow (note phase artifact [small arrows])

Fig 12-49 Extreme vertebrobasilar dolichoectasia causes a foramen of Monro mass in

this elderly patient Axial CT scan (A) without contrast enhancement shows a hyperdense

mass (arrow) at the foramen of Monro CECT scan (B) shows a sharply delineated,

strongly enhancing mass (arrows) Axial (C) and sagittal (D) T1-weighted MR scans

show the high-velocity signal loss (flow void) (large arrow) in the ectatic basilar artery

Note phase artifact (C, small arrows) Gradient-refocussed study (E) confirms flow in the

mass (arrow) (A and B, Courtesy E Fulton.)

Trang 34

Fig 12-50 Sagittal T1-weighted MR scan in this 12-year-old girl shows a mass (arrows) on the infefior floor of the third ventricle

Low-grade astrocytoma was found at surgery

Fig 12-51 Coronal T1-weighted MR scan shows a

mixed signal mass (arrows) within the third ventricle

This "popcornlike" appearance is typical for

cavernous angioma

lar extension of a pituitary adenoma, diaphragma sellae

meningioma, giant aneurysm, or craniopharyngioma

Other masses that involve the third ventricule include

thalamic anaplastic astrocytoma or glioblastorna

multiforme Metastases and lymphoma involve the

an-terior recesses, hypothalamus, and, often, the infundibular

stalk

Primary third ventricle tumors in adults are rare A third

ventricle meningioma can arise either from choroid plexus

stromal cells or from the tela choroidea Very rarely a

pituitary adenoma is found entirely within the third

ventricle

Examples of nonneoplastic masses in the anteroinferior

third ventricle are histiocytosis in children and sarcoidosis

in adults (see subsequent discussion) Vascular

malformations (Fig 12-51) and cysts (glioependymal,

choroid, or inflammatory cysts) are also sometimes found

in the third ventricle.62

Aqueduct The cerebral aqueduct (of Sylvius)

communicates anterosuperiorly with the third ventricle and posteroinferiorly with the fourth ventricle It is bordered posteriorly by the tectum (quadrigeminal plate) and anteriorly by the periaqueductal gray matter of the midbrain (tegmentum)

Stenosis is the most common intrinsic aquedutal

abnormality Congenital stenosis often results in

severe obstructive hydrocephalus Acquired aqueductal stenosis is caused by midbrain tumors

such as astrocytoma or metastasis Ependymitis and

intraventricular hemorrhage sometimes obstruct the

aqueduct47 (Fig 12-52)

Fourth ventricle Primary fourth ventricular

neo-plasms are common in children but rare in adults

Pediatric tumors Cerebellar astrocytomas are the

most common posterior fossa tumor in children63 and

Fig 12-52 Axial T1-weighted MR scan shows

A4 hemorrhage (arrows) within the cerebral

aqueduct

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Fig 12-53 Axial postcontrast T1-weighted MR

scan shows a cystic astrocytoma of the vermis The

nonneoplastic cyst wall (arrowheads) does not enhance; the mural nodule (curved arrow) shows strong but heterogeneous enhancement

Fig 12-54 Pilocytic astrocytoma of the fourth ventricle (arrows) is shown on

(A) axial CECT and (B) sagittal T1-weighted MR scans

account for about one quarter of all fourth ventricular

tumors in this age group.64 Most cerebellar astrocytomas

are the pilocytic type The most common appearance is

that of a large cystic mass with a mural nodule.21

Cerebellar astrocytomas usually originate from the vermis

and extend anteriorly into the fourth ventricle (Fig

12-53), although occasionally entirely intraventricular

tumors are seen (Fig 12-54)

Medulloblastoma (posterior fossa primitive

neuroec-todermal tumor or PNET-MB) is the second most

common posterior fossa tumor in children, accounting for

25% of all intracranial tumors in this age group.21 Ninety

percent of PNET-MBs are midline posterior fossa tumors

that originate in the inferior vermis and fill the fourth

ventricle (Fig 12-55).10 Subarachnoid dissemination is

common (see Chapter 14)

Ependymomas account for about 10% of all

pediat-ric brain tumors and are the third most common fourth ventricular neoplasm in children.64 Ependymomas arise in the ependymal lining of the fourth ventricle and extend into the lateral recesses and through the foramina of Luschka into the cerebellopontine angle

cisterns (see Fig 13-51, A) Posteroinferior extension

through the foramen of Magendie into the cisterna

magna is also common (see Fig 12-95)

The fourth most common posterior fossa mass in

children is brainstem glioma.63 About one quarter are low-grade medullary astrocytomas with a dorsal ex-ophytic component that grows posteriorly into the 20 fourth ventricle.20

Other than medulloblastoma, ependymoma, and astrocytoma, fourth ventricular tumors in children

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Fig 12-55 A, Coronal postcontrast CT scan shows a classic medulloblastoma (arrows)

The midline posterior fossa mass enhances strongly but somewhat inhomogeneously B,

Axial postcontrast T1-weighted MR scan in this 4-year-old child shows a lobulated,

strongly enhancing mass in the fourth ventricle (arrows) Ependymoma

Fig 12-56 A 54-year-old man with known oat cell carcinoma had headaches, nausea,

and vomiting A, CECT scan shows a mildly enhancing lobulated mass in the fourth

ventricle (arrows) B, Sagittal Tl-weighted MR scan shows the mass fills the fourth

ven-tricle and extends posteriorly into the cisterna magna No other CNS lesions were tified Surgery disclosed metastatic oat cell carcinoma

iden-are riden-are Choroid plexus papilloma, ganglioglioma, and

dermoid cyst are uncommon tumors that can occur in

this location

Adult tumors The most common fourth ventricular

neoplasm in an adult is metastasis (Fig 12-56) Primary

intraaxial posterior fossa neoplasms in adults are rare.23

Hemangioblastoma is the most frequent of these

uncommon lesions Most hemangioblastomas are

located in the paramedian cerebellum, but large tumors

can compress or distort the fourth ventricle

Primary fourth ventricular tumors such as choroid

plexus papilloma, epidermoid, or dermoid tumors are

rare (Fig 12-57) Subependymomas occur in the

inferior fourth ventricle near the obex and are usually

found incidentally in older patients (see Chapter 13)

Nonneoplastic masses Inflammatory cysts, vascular

malformations, and other benign lesions are casionally seen within the fourth ventricle (Fig 12-58).

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oc-Fig 12-57 Axial CECT scan in a 42-year-old patient

with headaches shows a moderately enhancing,

partially calcified fourth ventricular mass (arrows)

Choroid plexus papilloma was found at surgery

Fig 12-58 Sagittal (A) and axial (B) T1-weighted MR scans show a cystic

fourth ventricular mass (arrows) Intraventricular cysticercosis cyst was found at surgery (Courtesy C Sutton.)

Cerebellopontine Angle Masses

Normal anatomy The cerebellopontine angle (CPA)

cistern lies between the anterolateral surface of the pons

and cerebellum and the posterior surface of the petrous

temporal bone (Fig 12-59) Important structures within

the CPA cistern include the fifth, seventh, and eighth

cranial nerves, the superior and anterior inferior

cerebellar arteries, and tributaries of the superior petrosal

veins.65

The trigeminal nerve (CN V) arises from the middle of

the pons at the cerebellopontine angle and courses

anteriorly through the superolateral aspect of the cistern

The facial (CN VIII) and vestibulocochlear (CN VIII)

nerves arise in the inferior part of the cistem and course

laterally across the CPA cistern into the internal auditory

canal The flocculus, a lobe of

the cerebellar hemisphere, projects into the CPA tern behind the seventh and eighth cranial nerves The superior and anterior inferior cerebellar arter-ies arise from the basilar artery and course postero-

cis-laterally through the CPA cistern (see Chapter 6)

Veins from the pons, middle cerebellar peduncle, and cerebellopontine fissure unite near the trigeminal nerve and form the superior petrosal veins.65

Lesions in the CPA cistern can arise from the brain, temporal bone, or subarachnoid space and its contents The majority of CPA masses are located pri-marily in the cistern Others arise within the internal auditory canal itself, and some originate in the adjacent brain or skull and extend into the CPA secondarily (Fig 12-60)

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Cerebellopontine Angle (CPA) Cistern

Lesions

Imaging signs of extraaxial masses

Ipsilateral CPA cistern enlarged

CSF/vascular "cleft" between mass and cerebellum

Displaced gray-white matter interface around mass

Brainstem rotated

Fourth ventricle compressed (nonspecific)

Modified from Curnes JT: MR imaging of peripheral

intracranial neoplasms: extraaxial versus intraaxial masses,

J Comp Asst Tomogr 11:932-937, 1987

Cerebellopontine angle (CPA) cistern masses

CPA masses are uncommon in children but very common

in adults The majority of CPA tumors in adults are extraaxial.66 Imaging findings that distinguish extra- from intraaxial masses (see box) include the following:

1 Enlarged CPA cistern

2 A CSF "cleft" between the mass and adjacent brain

3 Brainstem rotation

4 Displaced cerebellar hemisphere cortex (Fi 12-61)

Fig 12-59 Anatomy of the cerebellopontine angle is

de-picted A, Axial cryomicrotome section through the

cerebellopontine angle cistern and temporal bone Axial

(B) and coronal (C) T2-weighted MR scans are shown:

1, Cerebellopontine angle cistern 2, CN V (trigeminal nerve) 3, CN VI (abducens nerve) 4, CN VII (facial nerve) 5, CN VII (vestibulocochlear nerve) 6, Internal auditory canal 7, Jugular foramen 8, Cochlea 9, Vestibule, semicircular canals 10, Anterior inferior cerebellar artery 11, Petrosal veins 12 Pons 13, Flocculus of cerebellum 14, Lateral recess of fourth ventricle 15, Choroid plexus (Courtesy W

Rauschning.)

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Cerebellopontine angle cistern

Common Schwannoma (acoustic neuroma) Meningioma

Vascular ectasia /aneurysm Epidermoid

Other schwannomas (e.g., trigeminal) Uncommon

Metastasis Parganglioma Arachnoid cyst Lipoma

Meningitis

Internal auditory canal

Common Schwannoma Postoperative changes Uncommon

Neuritis

Brainstem/cerebellum

Uncommon Exophytic glioma Metastasis Hemangioblastoma Vascular malformation

Temporal bone

Uncommon Cholesterol granuloma Malignant otitis Gradenigo syndrome Paraganglioma Metastasis Rare Chordoma

Fig 12-60 Anatomic diagram depicts the cerebellopontine angle anatomy

Lesions that arise from each component are indicated

Fourth ventricle/ lateral recess

Uncommon Ependymoma Choroid plexus papilloma Rare

Medulloblastoma Astrocytoma

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Fig 12-61 Characteristic pathology and anatomy of the

most common cerebellopontine angle (CPA) mass, vestib-

ulocochlear schwannoma A, Anatomic specimen shows a

large CN VIII schwannoma (large arrows) Note the

"cleft" (small arrows) between the mass and the adjacent

characteristic abnormalities seen with an extraaxial CPA

mass: enlarged impslateral CSF cistern, CSF "cleft"

between the mass and adjacent cerebellum, displaced or

"buckled" cerebellar cortex, and brainstem rotation (A,

Courtesy E Ross.)

Fig 12-62 "Pseudomasses" that can be mistaken

for a CPA lesion A, NECT scan with bone

windows shows a prominent asymmetric jugular

tubercle (arrow) B, Normal choroid plexus (on

contrast-enhanced CT or MR (arrows) C,

Flocculus of the cerebellum An incidental

meningioma (open arrows) is seen on this T1-weighted MR scan Floccular lobes (curved

arrows).

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