14 -MENINGIOMAS and OTHER NONGLIAL NEOPLASMS .

C H A P T E R Meningiomas and Other Nonglial Neoplasms Mixed Glial-Neuronal and Neuronal Tumors Ganglioglioma and Ganglioneuroma Gangliocytoma Lhermitte-Duclos Disease Dysembryoplastic Neuroepithelial Tumor (DNET) Central Neurocytoma Meningeal and Mesenchymal Tumors Meningioma Nonmeningotheliomatous Mesenchymal Tumors Hemangiopericytoma Hemangioblastoma Primary Melanocytic Lesions Pineal Region Tumors Germ Cell Tumors Pineal Cell Tumors Primitive Neuroectodermal Tumors Medulloepithelioma Medulloblastoma (Posterior Fossa PNET, i.e., PNET-MB) Primary Cerebral Neuroblastoma (Supratentorial PNET) Hemopoetic Tumors Approximately one half of all primary brain tumors are gliomas The other half are derived from a spectrum of nonglial sources We first turn our attention to an uncommon but fascinating group of primary neoplasms and neoplastic-like masses that represents a transition between glial and neuronderived tumors These are the ganglion cell tumors, dysplastic masses, and central neurocytoma We then consider the most common of all nonglial primary brain tumors: meningioma Our discussion of primary brain tumors next turns to a spectrum of other nonglial neoplasms that ranges from pineal germinomas and pineal parenchymal tumors to embryonal, or "primitive," tumors such as primitive neuroectodermal tumor (PNET) and medulloblastoma (PNET-MB) We conclude this chapter by discussing the uncommon but increasingly more frequent primary CNS lymphoma MIXED GLIAL-NEURONAL AND NEURONAL TUMORS This interesting group of unusual primary brain tumors includes the ganglion cell tumors, ganglioglioma and gangliocytoma, and central neurocytoma (see box p 580) Neoplasms that contain mature neurons are designated gangliogliorna or gangliocytoma Both are contingent on the microscopic identification of well-differentiated but neoplastic neurons within the tumor.1 Glial-neuronal tumors contain varying mixtures of differentiated but abnormal ganglion cells and glial 580 PART THREE Brain Tumors and Tumorlike Processes Ganglion Cell Tumors Ganglioglioma (mixed glial, neuronal elements) and ganglioneuroma (pure ganglionic tumor) Gangliocytoma (probably dysplastic brain, not a true tumor) Lhermitte-Duclos disease (dysplastic cerebellar gangliocytoma; probably a malformation, not a true neoplasm) Dysembryoplastic neuroepithelial tumor (DNET) Ganglioglioma Pathology Cyst with mural nodule Age, presentation Children, young adults with seizures Location Typically temporal, frontal lobes Imaging Well-delineated cyst with partially calcified mural, nodule most common; bone changes common if lesion is superficial stroma.2 Mixed tumors, designated gangliogliorna, are more common than pure ganglionic tumors (ganglioneuroma) Another type of ganglion cell tumor, gangliocytoma, is probably a dysplastic hamartoma similar to Lhermitte-Duclos disease Gangliocytoma must also be distinguished from hamartomas and migrational abnormalities Imaging studies can be critical in the preoperative diagnosis of these fascinating tumors Ganglioglioma and Ganglioneuroma Courville first used the term ganglioglioma in 1930 to describe an unusual primary CNS tumor that contained both neuronal and glial elements Ganglioglioma is thus conceptually a neoplasm that represents a transition between glial and nonglial tumors Pathology Gross pathology Gangliogliomas are usually small, firm, well-circumscribed masses A cyst with a partially calcified mural nodule is common3 (see box above right) Microscopic appearance Well-differentiated but neoplastic ganglion cells are mixed with glial stroma containing astrocytes or, occasionally, oligodendrocytes.2 The abnormal neurons in these tumors must be distinguished from neoplastic glia that may resemble neurons and from normal neurons intermixed with infiltrative glioma.1 So-called ganglioneuromas are ganglion cell tumors in which mature neuronal components are the dominant component Because they are histologically similar to and biologically indistinguishable from ganglioglioma, we will not consider them as a separate tumor Desmoplastic infantile ganglioglioma is an uncommon ganglioglioma subtype that occurs exclusively in infants These neoplasms are typically large cystic frontal-lobe tumors A meningeal-based nodule that has glial and ganglionic differentiation accompanied by an extreme desmoplastic reaction is usually present.4,5 Fig 14-1 Axial NECT scan in a 14-year-old with headache shows a large right frontal cystic mass (open arrows) with a calcified mural nodule (curved arrow) No enhancement was seen following contrast administration Ganglioglioma Age, clinical presentation, and natural history Gangliogliomas occur in children and young adults Between 60% to 80% of patients are under 30 years of age3 ; most become symptomatic during the second decade.6 Seizures are the most common presenting symptom,7,8,8a followed by signs of increased intracranial pressure.6 Gangliogliomas are very slow-growing tumors Symptoms have often been present for year and long-term survival is the rule, even with incompletely resected lesions.6 Very rare cases of leptomeningeal and subarachnoid dissemination of ganglioglioma have been reported.9,10 Chapter 14 Meningiomas and Other Nonglial Neoplasms 581 Fig 14-2 A 9-year-old girl with long-standing seizures had a contrast-enhanced CT scan A, Soft tissue windows show a cystic (straight arrows), partially calcified (curved arrow) high left parietal mass B, Slightly higher cut with bone window shows focal calvarial erosion (arrows) Ganglioglioma was found at surgery Incidence Reported incidence varies from 0.4% to 6%; the higher percentages reflect series with predominately pediatric patients.11 The overall frequency is probably 0.5% to 1% of all primary CNS neoplasms.8 Location Although gangliogliomas may occur in any location, the majority are supratentorial The temporal lobe is the most common site, followed by the frontal and parietal lobes.12,13 The cerebellum is also a reported site.14,15 Imaging CT The classic appearance is a cyst with an isoor hypodense mural nodule that is often calcified (Fig 14-1).7,8 However, gangliomas have variable density and contrast enhancement patterns, and calcification may be inconspicuous.6 Because these tumors are slow growing, peripherally located ganglioliomas may cause scalloped pressure erosion of the overlying calvarium (Fig 14-2) MR MR findings are also nonspecific The most common appearance is a well-delineated frontal or temporal lobe mass that is hypointense on T1- and hyperintense on T2-weighted sequences (Fig 14-3 A and B).16 Enhancement varies from none to striking.15 Nodular, rim, and solid enhancement patterns all occur (Fig 14-3 C).8,15,16 Gangliocytoma The term gangliocytoma has been used to describe purely neuronal tumors that lack a glial component and not show neoplastic change.17 Most, if not all, of the reported cases are probably dysplastic brain.17,18 Histologic studies in patients with malformative disorders such as unilateral megalencephaly may show bizarre-appearing neurons associated with an increase in the number and size of astrocytes.19 MR imaging in cases with the microscopic diagnosis of gangliocytoma often shows clear evidence for brain malformation and dysplasia rather than neoplasia (Fig 14-4) Lhermitte-Duclos Disease Lhermitte-Duclos disease, also known as dysplastic cerebellar gangliocytoma, is characterized by progressive hypertrophy of the cerebellar folia The etiology of this disorder is controversial, and satisfactory classification is difficult Lhermitte-Duclos disease is probably a brain malformation and not a true neoplasm The normal cerebellar cortex consists of the following three layers: Outer, or molecular, layer Purkinje (middle) layer Inner, or granular, layer In Lhermitte-Duclos disease an abnormal population of large neurons is present in the granular layer and there is aberrant myelination in the molecular layer.20 The cerebellar cortex appears grossly thickened and dysplastic MR findings are those of an expanding mass with laminated, increased signal on T2WI (see Figs 4-16 and 4-17) 582 PART THREE Brain Tumors and Tumorlike Processes Fig 14-3 Long-standing temporal lobe seizures in this 24-year-old patient prompted MR examination A, Axial T1-weighted scan without contrast enhancement shows a welldelineated mass (arrows) that is slightly hypointense compared to surrounding brain B, The mass (arrows) is hyperintense on T2WI C, Postcontrast T1WI shows nodular rim enhancement (arrows) Ganglioglioma was found at temporal lobe resection (Reprinted from Osborn AG, Hendrick RE: Categorical course on MR imaging, Radiological Society of North America, 1990 With permission.) Dysembryoplastic Neuroepithelial Tumor (DNET) Dysembryoplastic neuroepithelial tumor (DNET) is a newly described pathologic entity that is sometimes the underlying cause for partial complex seizures Pathologically these tumors are benign lesions that are occasionally cystic and show at least one of the following three characteristics:21,21a Specific glioneuronal element Nodular component Association with cortical dysplasia MR scans show a focal cortical (usually temporal lobe) lesion that is hypointense on T1- and hyperirttense on T2-weighted studies Some cases resemble benign cysts with slightly increased signal on proton density-weighted sequences Differentiation from low-grade astrocytoma and gangliogliorna MR is not possible.22 Fig 14-4 MR scan was performed in a 6-year-old child with seizures Axial T1WI shows a right hemisphere mass (arrows) that is isointense with gray matter Low signal foci (arrowheads) are seen within the mass Biopsy showed mature but disorganized neurons and ganglion cells and was called gangliocytoma This is a dysplastic cerebral hemisphere with heterotopic gray matter The low signal area is a partially formed ventricle (Courtesy P Davis.) Central Neurocytoma Central neurocytoma is a recently recognized dinicopathologic entity that is histologically 4istinct from ganglion cell tumors, neuroblastomas, and primitive neuroectodermal tumors Central neurocytomas have morphologic and immunohistochemical features of neuronal differentiation.22a Pathology Gross pathology Central neurocytoma is a well-defined, sharply circumscribed, lobulated intraven- Chapter 14 tricular mass that typically lies adjacent to the foramen of Monro or septum pellucidurn1 (see box) Necrosis and cyst formation are common.3 Some neurocytomas are extensively vascularized23; frank intraventricular hemorrhage can occur but is uncommon.24 Microscopi c appearance Light microscopy shows features that are indistinguishable from oligodendroglioma Electron microscopy demonstrates the neurosecretory granules, synapses, microtubules, and neuritic processes that confirm the neuronal origin of this tumor Immunohistochernical studies show consistent and uniform expression of the neuronal Meningiomas and Other Nonglial Neoplasms marker proteins, synaptophysin.23,25 neuron-specific 583 enolase Age, clinical presentation, and natural history Age Neurocytomas are tumors of young adults The average age of reported patients is 31 years, ranging from 17 to 53 years26 Duration of clinical symptoms is usually less than months Common presentation is headache with signs of increased intracranial pressure.26 A striking characteristic of central neurocytoma is its benign biologic activity A recent review reported survival up to 19 years; no patients had died from tumor growth or recurrent neoplasm.24 Incidence Central neurocytomas account approximately 0.5% of primary brain tumors.23,27 Central Neurocytoma Pathology Looks like oligodendroglioma on light microscopy Electron microscopy shows neurosecretory granules, synapses Immunohistochemistry shows neuronal marker proteins (e.g., synaptophysin) Age Young adults Location Lateral ventricles near foramen of Monro Imaging Inhomogeneous, partially calcified, mildly enhancing lateral ventricular mass and for Location The lateral ventricle is the most common site; most central neurocytomas are located adjacent to the foramen of Monro No tumor involved the occipital or temporal horns or atria of the lateral ventricles All but one case were confined to the ventricles A few cases that extended into the third ventricle were reported; to date, none is reported in the fourth ventricle.28 Three cases of hemispheric (cerebral) neurocytomas have been reported.28 Imaging Angiography Angiographic findings are reported in only a few cases Some tumors show moderate to marked vascularity, although most are avascular masses that produce moderate ventricular enlargement (Fig 14-5, A).23 Fig 14-5 Typical imaging findings of a central neurocytoma Right internal carotid angiogram, venous phase, lateral view, (A) shows elongated, stretched subependymal veins (arrows), indicating moderate hydrocephalus No vascular stain was identified Continued 584 PART THREE Brain Tumors and Tumorlike Processes Fig 14-5, cont'd Pre- (B) and postcontrast (C) axial T1-weighted MR scans show a mixed hypo-/isointense right lateral ventricular mass (arrows) that enhances moderately but inhomogeneously following contrast administration Central neurocytoma was found at surgery CT NECT scans show an iso- or slightly hyperdense mass within the body of the lateral ventricle adjacent to the foramen of Monro Most central neurocytomas contain multiple small cysts and exhibit a characteristic broad-based attachment to the superolateral ventricular wall.29 Tumor calcification is seen in the majority of cases and is usually clumped, coarse, or globular.26 Contrast enhancement is mild to moderate Hydrocephalus is almost always present.30 MR Most neurocytomas are inhomogeneously isointense on T1WI Low or absent signal areas are seen with calcific foci and tumor vessels Signal on T2-weighted sequences is variable; some neurocytomas remain relatively isointense with cortex, whereas others are moderately hyperintense Contrast enhancement is inhomogeneous and varies from none to moderate (Fig 14-5, B and C).30 The imaging differential diagnosis of central neurocytoma includes other intraventricular tumors that occur in young adults, i.e., oligodendroglioma, subependymal giant cell astrocytorna, low-grade or pilocytic astrocytorna, and ependymoma.31 MENINGEAL AND MESENCHYMAL TUMORS The meninges have been called bland fibrous vestments of a magnificent organ However, as the same neuropathologists who made that observation have noted, the cranial meninges have their own special spectrum of distinctive and important pathologic lesions.1 In this section we consider meningeal neo- Meningeal and Mesenchymal Tumors Meningioma Nonmeningotheliomatous mesenchymal tumors Benign osteocartilagenous tumors (e.g., osteoma, enchondroma) Malignant mesenchymal tumors (chondrosarcoma, fibrosarcoma, angiosarcoma) Primary melanocytic lesions Hemangiopericytoma Hemangioblastoma plasms, beginning with meningiomas, and then dis cuss nonmeningothelial mesenchymal neoplasms such as angiosarcoma and fibrosarcoma (see box) We conclude by discussing two related tumors: hemangiopericytoma and hemangioblastoma Meningioma Although a broad spectrum of neoplasms can originate from the cranial meninges, meningioma is by far the most common.32 Meningioma is the most common nonglial primary brain tumor.3 We begin our discussion of these important neoplasms by delineating their etiology and pathology, then turn to the various imaging features of meningiomas Etiology Histologic, chromosomal, biochemical and receptor studies have significantly advanced the understanding of meningioma pathogenesis.33,34 Chapter 14 Meningiomas and Other Nonglial Neoplasms 585 Fig 14-6 A, The dura and superior sagittal sinus (SSS) from an autopsy case are seen from above The SSS is opened to show the numerous arachnoid granulations (arrows) that project into its lumen B, Autopsy specimen illustrates the location and appearance of a typical small convexity meningioma (arrow) Note invaginated adjacent brain (A, Courtesy E Ross B, From Okazaki H, Scheithauer B: Slide Atlas of Neuropathology, Gower Medical Publishing With permission.) Histology Any meningothelial cell, whether intracranial, intradiploic, spinal, or ectopic, can potentially give rise to a meningioma.33 Most meningiomas originate from specialized meningothelial cells in arachnoid granulations, the so-called arachnoid cap cells (Fig 14-6).34 A few meningiomas probably arise from dural fibroblasts, whereas others arise from the arachnoid that is associated with cranial nerves and the choroid plexus Cytogenetics Chromosome 22 is important in the pathogenesis of meningiomas.34a Monosomy occurs in 72% of cases and long-arm deletions are common.34 Neurofibromatosis type (NF-2) is the major gen4ic condition that predisposes to meningioma formation (see Chapter 5) Receptor activity Several clinical features suggest meningiomas may be related to sex hormones Meningiomas are more common in women, are correlated positively with breast carcinoma, and sometimes increase in size during pregnancy Progesterone and, possibly, estrogen or androgen receptors have been demonstrated in many meningiomas.34 Miscellaneous factors Radiation therapy appears to be a predisposing factor in the development of some meningiomas Pathology Gross pathology Meningiomas assume two basic gross morphologic configurations: a spherical or lobulated mass that is sometimes termed "globose" meningioma (Fig 14-7, A) and a flatter, carpetlike -en plaque" lesion that infiltrates dura and also sometimes invades underlying bone (Fig 14-7, B).1 The dural attachment that underlies most meningiomas can be broad, giving rise to a sessile-appearing tumor, or narrow and stalklike with a pedunculated tumor mass Meningiomas are usually sharply circumscribed lesions with a well-delineated tumor-brain interface.35 The surface of most meningiomas appears lobulated or bosselated A distinct "cleft" of arachnoid with trapped CSF and prominent vessels that surround the extraaxial mass is often observed (Fig 14-8).36 Consistency of meningiomas varies from soft to tough or even gritty, depending on the fibrous tissue or calcification present.1 Necrotic and hemorrhagic foci are often present, although gross hemorrhage is uncommon Cystic and xanthomatous changes are sometimes observed.1 A "collar" of reactive thickened dura often surrounds the meningioma base (see subsequent discussion) Classification and microscopic appearance Recent advances in the pathologic delineation of meningiomas include the development of a simplified classification system, the use of markers to evaluate meningioma proliferative activity and potential aggressiveness, and the delineation of malignant phenotypes Several classification schemes for categorizing 586 PART THREE Brain Tumors and Tumorlike Processes Fig 14-7 A, Autopsy specimen illustrates a typical "globose" meningioma (large arrow) Note collar of thickened reactive dura (small arrows) that surrounds its attachment site B, A sphenoid wing meningioma has a flatter, "en plaque" appearance (arrows) (A, From Royal College of Surgeons of England, Slide Atlas of Pathology, Gower Medical Publishing By permission B, From Okazaki H, Scheithauer B: Slide Atlas of Neuropathology, Gower Medical Publishing With permission.) Fig 14-8 Coronal autopsy specimens of a patient with a large sphenoid wing meningioma A, The tumor is seen in situ The mass (large arrows) has invaginated deeply into the brain Note distinct cleft (arrowheads) that separates the tumor from adjacent brain A fibrous pseudocapsule is indicated (double white arrows) Displaced cortex (double black arrows) indicates the extraaxial location of the mass B, Specimen with the tumor removed shows the fibrous pseudocapsule (arrows) (Reprinted from Sheporaitis L, Osborn AG et al: Radiologic-pathologic correlation of intracranial meningioma, AJNR, 13:29-37, 1992.) meningiomas have been promulgated (see box) Russell and Rubinstein's modification of Cushing's system divides these tumors into meningotheliomatous (syncytial), fibrous, transitional, and angioblastic types The World Health Organization (WHO) divides meningiomas into three basic categories: (1) meningioma (i.e., the common or typical "benign" meningioma), (2) atypical meningioma, and (3) anaplastic (malignant) meningioma.36a Meningiomas are histologically heterogeneous neoplasms Psammomatous calcifications and meningothelial cells that aggregate into whorls and lobules are present in many-but by no means all-meningiomas These features characterize the so-called meningotheliomatous, or syncytial, meningioma Other meningiomas have interlacing sheets and fascicles of markedly elongated spindle-shaped cells that sometimes exhibit a prominent storiform appearance Abundant reticular and collagenous fibers are common in this type of meningioma, the so-called fibrous Chapter 14 Meningiomas and Other Nonglial Neoplasms 587 Classification of Meningiomas Classic description Meningotheliomatous (syncytial) meningioma Fibrous meningioma Transitional meningioma Angioblastic meningioma World Health Organization (WHO) Meningioma (typical "benign" meningioma) Atypical meningioma Anaplastic (malignant) meningioma meningioma Other meningiomas exhibit a mixture of these features and represent a "transitional,, type.1 Some meningiomas are highly cellular and very vascular These tumors, formerly called "angioblastic " meningiomas, are probably tumors that arise from blood vessels and are now classified as hemangiopericytomas (see subsequent discussion) Little prognostic significance can be attached to the morphologic variations of meningiomas, described Previously.1 Many neuropathologists now use the simple WHO classification, which correlates with biologic behavior (see subsequent discussion) and is therefore the preferred system In the WHO classification, 88% to 94% of meningiomas are benign or typical, 5% to 7% are atypical, and only 1% to 2% are anaplastic or malignant.37,38 Incidence Meningiomas are the most common nonglial primary brain tumor and the most common intracranial extraaxial neoplasm33 (see box, right) They account for 15% to 20% of all primary brain tumors Meningiomas occur at a rate of or per 100,000 population.34 Age, gender, and clinical presentation Age and gender Meningiomas are basically adult tumors; the peak occurrence is between 40 and 60 years of age Incidence in women outnumbers that In men-2:1 to 4:1.33 Only 1% to 2% of all meningiomas occur in children less than 16 years of age.34 Meningiomas account for 1% to 3% of pediatric intracranial tumors.39,40 When they occur in this age group they are often located in unusual sites such as the posterior fossa or lateral ventricles (Fig 14-9).34,34c Clinical presentation Less than 10% of all meningiomas ever cause Symptorns.41 Many are discovered incidentally on imaging studies or at autopsy Clinical manifestations associated with symptomatic meningiomas vary significantly with location Seizure and hemiparesis are common presentations Meningioma: Etiology and Epidemiology Etiology Arise from specialized meningothelial cells called arachnoid "cap" cells Chromosome 22 (association with NF-2) Progesterone, estrogen receptors in meningiomas Incidence Most common nonglial primary CNS tumor 15% to 20% of primary brain tumors Subtypes 88% to 95% typical meningioma 5% to 7% atypical meningioma 1% to 2% anaplastic (malignant) meningioma Multiple in 1% to 9% Part of NF-2 syndrome Age, gender Peak incidence 40 to 60 years Rare in children (often atypical location or histology) Female: male = 2:1 to 4:1 Natural history Most important factors are location, resectability Local recurrence rate varies Metastases rare, but both benign and malignant men ingiomas can metastasize for convexity or parasagittal tumors Basisphenoid lesions usually cause visual field defects, whereas cavernous sinus meningiomas are associated with multiple cranial nerve palsies Frontal (cribriform plate) meningiomas often become very large before causing symptoms other than anosmia Location (see box, p 588) Most meningiomas are extraaxial dural-based lesions Ninety percent are supratentorial.42 Meningiomas typically occur along intradural venous sinuses, at the confluences of multiple cranial sutures and at other sites where arachnoid granulations and arachnoid cell rests occur (Fig 14-6).42 The parasagittal region and cerebral convexities are common sites (Fig 14-10; see box, p 588), accounting for nearly half of all meningiomas Convexity meningiomas arise from the dura that overlies the cerebral hemispheres The coronal suture is a common site Most parasagittal meningiomas arise along the middle third of the superior sagittal sinus (SSS); only 15% occur along the posterior SSS.42 Parasagittal meningiomas often grow into and then occlude the SSS A third common site is the sphenoid ridge Approximately one third of these tumors originate around the anterior clinoid process and often involve 588 PART THREE Brain Tumors and Tumorlike Processes Fig 14-9 A, Sagittal postcontrast T1-weighted MR scan in this 8-year-old girl without neurofibromatosis shows a large, intensely enhancing intraventricular mass (arrows) B, Axial T2WI shows the mass (arrows) is mostly isointense with cortex Meningioma Meningioma Location General Arachnoid granulations, along dural sinuses, at sutures Specific 25% parasagittal 20% convexity 15% to 20% sphenoid ridge 5% to 10% olfactory groove 5% to 10% parasellar 10% posterior fossa (near porus acousticus, along clivus) 2% other (intraventricular, pineal region, optic nerve sheath) 1% extracranial (nose, sinuses, skull) the optic canal The remainder arise along the middle or lateral (pterional) aspects of the sphenoid wing.42 Sphenoid wing meningiomas are often en plaque tumors Anterior basal or olfactory groove meningiomas account for 5% to 10% of meningiomas These tumors often attain large size before causing symptoms other than anosmia Another 5% to 10% of meningiomas arise in the sellar region Juxta- and suprasellar meningiomas can originate from the cavernous sinus dura, tuberculum, dorsum, or diaphragma sellae and cause cranial nerve palsies or visual symptoms Cavernous sinus meningiomas can be either uni- or bilateral and often extend posteriorly to involve the tentorium Posterior fossa sites account for approximately 10% of meningiomas The posterior surface of the petrous temporal bone and clivus are the most common infratentorial locations Approximately 2% of intracranial nieningiomas have no dural attachment These tumors arise from choroid plexus stromal cells or the tela choroidea and grow as intraventricular masses43 (Fig 14-9) are usually confined to the ventricles but occasionally penetrate into adjacent brain (see Fig 14-33).42 h uncommon meningioma sites include the optic nerve sheath and pineal region Approximately 1% of meningiomas arise outside the CNS dura The most common extradural site is the paranasal sinuses Other locations include the nasal cavity, parotid gland, and even the skin.44-46 primary calvarial meningiomas are rare They have been reported in the diploic, calvarial, extra-calvarial, and subgaleal spaces.47 Meningioma locations are depicted in Fig 14-10 Multiple meningiomas occur in 1% to 9% of imaged cases48; 16% are multiple at autopsy.42 Most occur in women Multiple meningiomas should be differentiated from meningiomatosis, a manifestation of neurofibromatosis type (NF-2) (see Figs 5-17 to 5-22) Natural history The most important factors in clinical outcome of meningioma are location and resectability.49 Tumors with the same histologic pattern Chapter 14 Meningiomas and Other Nonglial Neoplasms Fig 14-45 Axial NECT scan (A) with diffuse ependymal spread of germinoma A thick hyperdense rind of tumor (arrows) encases the lateral ventricles MR scans show the tumor is hyperintense on T1WI (B, arrows) and quite hypointense on T2WI (C, arrows) Fig 14-46 Classic MR findings of pineal germinoma The lobulated pineal region mass (arrows) is isointense with cortex on T1- (A), proton density- (B), and T2-weighted (C) sequences 611 612 PART THREE Brain Tumors and Tumorlike Processes Fig 14-47 Sagittal T1-weighted MR scans in a newborn infant with bulging fontanelles show a huge mixed signal mass that involves the third and both lateral ventricles Teratoma was found at surgery Fig 14-48 A 32-year-old woman had a history of headache and Parinaud's syndrome at age 15 Pneumoencephalogram, had demonstrated a "pinealoma." She was shunted and radiated CT and MR scans were obtained 17 years later because of increasing headaches and recurrent Parinaud's syndrome A, Axial CECT scan shows a mixed density enhancing pineal and thalamic mass (arrows) B, Axial T1-weighted MR scan shows a hypo- and isointense mass (arrows) Biopsy disclosed pineocytoma Pineal Cell Tumors Pineal parenchymal neoplasms account for less than 15% of all pineal region tumors.90 There are two basic types of pineal cell neoplasms: pineocytoma and pineoblastoma (see box) Pineocytoma Pineocytoma is a benign tumor that arises from pineal parenchymal cells Pineocytomas are uncommon, accounting for only 0.4% to 1% f all primary brain tumors Unlike other pineal neoplasms, there is no male preponderance Pineocytomas also occur a decade or two later; the average age diagnosis is 34 years.95 Pineocytomas grow slowly, closely resemble normal pineal gland parenchyma on histologic examination, and rarely disseminate in the CSF space.96 No Chapter 14 Meningiomas and Other Nonglial Neoplasms 613 Pineal Cell Tumors Pineocytoma Uncommon (