Central Nervous System

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Figure 43.22 Neurocysticercosis. Typical of cerebral Taenia solium infestation is the solitary, encysted scolex demonstrated in this neurosurgi- cal specimen from the left frontal cortex of a 32-year-old Haitian man with a history of seizures

Figure 43.23 Neurocysticercosis. The parasite's main structural features include a prominent investing tegument or "cuticle," aggregated subcu- ticular cells, smooth muscle fibers, and four suckers, one of which is depicted at upper left

Figure 43.24 Toxoplasmosis. Minute, basophilic structures representing bradyzoites fill a protozoal pseudocyst with associated infiltrating lym- phocytes, plasma cells, and macrophages

Figure 43.25 Herpes Simplex Encephalitis (HSE). As shown here, HSE may masquerade as a noninfectious, ischemic process (particularly if biopsied early in its clinical evolution). Note the noninflammatory appear- ance, neuronal shrinkage, pyknosis, and dissolution. The nucleus of a cell in the center of this field contains a well-defined Cowdry A inclusion body

Figure 43.26 Herpes Simplex Encephalitis. In this immunoperoxidase preparation, the cytoplasm of neurons and inclusion bodies within the nuclei of satellite glia are labeled by antibodies to herpes simplex type 1

Figure 43.27 Progressive Multifocal Leukoencephalopathy. A postcontrast injection magnetic resonance imaging demonstrates the regional white matter hypodensity, absence of mass effect or abnormal enhancement, and cortical preservation that typify this demyelinating infection

Figure 43.28 Progressive Multifocal Leukoencephalopathy. JC virus-infected oligodendrocytes in the left of this field exhibit the nuclear swelling, chromatin dissolution, and replacement by amphophilic, "ground- glass" inclusion material that is peculiar to this disorder

Figure 43.29 Progressive Multifocal Leukoencephalopathy. Grotesque cytologic alterations may result from infection of astrocytes by the JC virus. An accompanying infiltrate of foamy macrophages should militate strongly against the diagnosis of neoplasia, despite the worrisome appearances of these bizarre cells

Figure 43.30 Human Immunodeficiency Virus Encephalitis. Non- granulomatous infiltrates centered loosely about blood vessels in the cerebral white matter (shown here) or basal ganglia and dominated by macrophages, including multinucleated forms resulting from retrovirally mediated cell fusion, characterize infection of the central nervous system by this agent. The associated astrogliosis and spongy rarefaction are common accompanying features

Figure 43.31 Creutzfeldt-Jakob Disease. Noninflammatory vacuolization of the cerebral cortex is the dominant alteration evident in this biopsy specimen from an elderly man with progressive dementia and myoclonus. This change typically precedes conspicuous neuronal dropout and astrogliosis, the other dominant findings in this prion-related disorder

Figure 43.32 Diffuse astrocytoma forming secondary structures of Scherer, including subpial accumulation, perivascular aggregates, and perineuronal satellitosis

Figure 43.33 Genetic Model of Diffuse Gliomas. The left and middle columns represent the IDH-mutant subtypes, while the right column represents the most common IDH-wildtype categories. m, mutant; wt, wildtype; 1p19q-codel, 1p/19q codeletion

Figure 43.34 Diffuse Astrocytoma With Fibrillary Cytology. Note the appearance of "naked nuclei" with tumor cells seemingly embedded in a fibrillar background but containing irregular hyperchromatic nuclei with no discernable cytoplasm

Figure 43.35 Gemistocytic Astrocytoma. Heavily dominated on initial resection by the large gemistocytes shown here, this example recurred 11 months after radiotherapy and chemotherapy. Re-resection demon- strated progression to glioblastoma. Note that these cells retain the oval and somewhat vesicular nuclei of astrocytes. For a comparison with the "minigemistocytic" variant of oligodendroglioma, see Fig. 43.61B

Figure 43.36 Diffuse Astrocytoma. Neuroradiological features common to the low-grade fibrillary astrocytoma in postcontrast magnetic resonance imagings, such as this temporal example, include generalized expansion and hypodensity of infiltrated regions with only modest mass effect, and no foci of bright signal enhancement that would indicate blood-brain barrier disruption

Figure 43.37 Diffuse Astrocytoma. T2-weighted magnetic resonance imaging showing an ill-defined fronto-temporal mass with increased signal intensity

Figure 43.38 Diffuse Astrocytoma. The insidious permeation typical of the fibrillary astrocytoma is illustrated in this anterior temporal lobectomy specimen. The gyrus at right maintains a clearly demarcated cortical ribbon over its digitate white matter. Moving to the left, there is diffuse gyral expansion and effacement of these landmarks, reflecting tumoral infiltration. No discrete mass is formed, and, as is characteristic of low- grade examples, there is no evident hemorrhage or necrosis (see Fig. 43.48 for comparison)

Figure 43.39 Diffuse Astrocytoma. Conspicuous cytoplasmic processes, mild nuclear pleomorphism, and only modest hyperchromasia are evi- denced by the cells of this well-differentiated astrocytoma. The absence of mitotic activity supports its classification as a low-grade lesion. Note the dyscohesive growth pattern

Figure 43.40 Diffuse Astrocytoma. Foreign to reactive astroglial proliferations, microcystic change is a particularly conspicuous feature of some low-grade astrocytomas

Figure 43.41 Diffuse Astrocytoma. A lack of cellular cohesion and conspicuous cytoplasmic processes-features that serve to distinguish astrocytomas from metastatic carcinomas, lymphomas, and other neoplasms are apparent in this intraoperative crush preparation

Figure 43.42 Diffuse Astrocytoma, IDH-mutant showing immunoreactiv- ity for the IDH1 R132H mutant protein. Note the immunonegative cortical neurons in the background

Figure 43.43 Diffuse Astrocytoma, IDH-Mutant. As in this example, most IDH-mutant astrocytomas additionally demonstrate loss of alpha- thalassemia mental retardation X-linked immunoreactivity in tumor nuclei. Note that non-neoplastic cells (endothelial, glial, inflammatory) retain expression serving as an internal positive control

Figure 43.44 Diffuse Astrocytoma, IDH-Mutant. As in this example, most IDH-mutant astrocytomas also show p53 overexpression by immunohistochemistry

Figure 43.45 Anaplastic Astrocytoma. Compared with its low-grade counterpart (see Fig. 43.39), this lesion exhibits increased cellularity, the cytologic features of a fully malignant neoplasm, and, at center, mitotic figures

Figure 43.46 Diffuse Midline Glioma (Glioblastoma), H3 K27M-Mutant. This thalamic glioblastoma was characterized as the new WHO entity of "diffuse midline glioma, H3 K27M-mutant" based on immunohistochemical detection of the mutant protein in tumor nuclei

Figure 43.47 Glioblastoma. In postcontrast injection computed tomography or (shown here) magnetic resonance studies, many glio- blastomas are characterized by a bright ("enhancing") ring (representing intact, abnormally vascularized tumor tissue in which the blood-brain barrier is disrupted) that surrounds a region of hypodensity (central necrosis). The gyriform temporal lobe enhancement below this basal ganglionic example attests to neoplastic infiltration beyond the deceptively well-delimited ring margin

Figure 43.48 Glioblastoma. Foci of hemorrhage and geographic yellow discoloration indicative of necrosis impart a variegated appearance to this example

Figure 43.49 Glioblastoma. Note the complex, "glomeruloid" quality of the microvascular proliferation at right. Astrocytic elements are seen at left

Figure 43.50 Glioblastoma. Dense cellularity, striking pleomorphism, and zones of coagulative necrosis lined by "palisading" tumor cells characterize the prototypical glioblastoma

Figure 43.51 Radiation Effects. A marked reduction in cellularity, extensive necrosis, and necrotizing fibrinoid vasculopathy with vascular thrombosis and ectasia typify astrocytic neoplasms injured by irradiation  

Figure 43.52 Radiation Effects. IDH1 R132H immunohistochemistry highlights residual postradiation astrocytoma cells with radiating processes, resembling reactive astrocytes

Figure 43.53 Gliosarcoma. A, Islands of astrocytic tumor tissue lie embedded in what otherwise appears to be a spindle cell sarcoma. B, Only the sarcomatous regions show dense intercellular reticulin deposition. In contrast, on immunoperoxidase assay (C), only astrocytic elements mark with glial fibrillary acidic protein

Figure 43.54 Glioblastoma, Small Cell Variant. In contrast to most glioblastomas, the small cell variant is relatively monomorphic with small, round to oval nuclei and minimal discernable cytoplasm. The presence of branching capillaries and clear haloes (not shown here) often invokes a differential diagnosis with anaplastic oligodendroglioma

Figure 43.55 Glioblastoma, Giant Cell Variant. This subtype is character- ized by numerous bizarre mononucleated and multinucleated giant cells, imparting a marked degree of pleomorphism that often raises a differential with pleomorphic xanthoastrocytoma

Figure 43.56 Glioblastoma, Granular Cell Variant. Although the granular to vacuolated cytoplasm of tumor cells is reminiscent of macrophages (thus raising a differential diagnosis with demyelinating disease), the larger cell size and presence of microvascular proliferation are clues to its malignant nature (A). Further confirmation of the tumor's glial nature may be established with glial fibrillary acidic protein (not shown) and/or OLIG2 (B) immunostains

Figure 43.57 "Glioneuronal Tumor With Neuropil Islands." This entity represents a variant of diffuse astrocytoma of any grade with superimposed neuronal/neurocytic differentiation manifesting in pale neuropil-rich islands (A) that are synaptophysin immunoreactive (B)

Figure 43.58 Glioblastoma With Primitive Neuronal Component (A, H&E; B, GFAP; C, Synaptophysin). This variant may arise from any diffuse glioma subtype, but astrocytomas are most common. They are characterized by sharp demarcation of a primitive-appearing component with diminished evidence of glial differentiation and increased evidence of neuronal differentiation. In this example, there is a gemistocytic astrocytoma component on the left giving rise to a primitive component on the right

Figure 43.59 Glioblastoma, Epithelioid Variant. A, This variant is often surprisingly demarcated in growth pattern and harbors large epithelioid to rhabdoid glioma cells reminiscent of malignant melanoma. B, Roughly half of cases express the BRAF V600E mutant protein by immunohistochemistry

Figure 43.60 Oligodendroglioma. The bright signal abnormalities seen in this nonenhanced computed tomography study of a large right cerebral oligodendroglioma represent foci of intratumoral calcification. While evidenced by only a minority of oligodendroglial neoplasms, linear or plate-like calcifications of this sort are most suggestive of the diagnosis

Figure 43.61 Oligodendroglioma. A, Uniform, round nuclei and clear perinuclear halos (artifacts of delayed fixation) typify well-differentiated oligodendrogliomas. "Minigemistocytic" variants (B) maintain oligoden- droglial nuclear features while amassing globose paranuclear expanses of eosinophilic, hyaline or whorling fibrillar cytoplasm. Compare the size of these cells and their cytologic features with those of the gemistocytic astrocytoma depicted at identical magnification in Fig. 43.35

Figure 43.62 Anaplastic Oligodendroglioma. Microvascular proliferation, readily apparent mitotic activity, and cytologic atypism are features of this example

Figure 43.63 Pilocytic Astrocytoma. This typical cerebellar example is characterized by a solid, brightly contrast-enhancing mural component and associated cyst on T1-weighted postcontrast magnetic resonance imaging

Figure 43.64 Pilocytic Astrocytoma. The biphasic cellular populations and architecture of the classic pilocytic astrocytoma are in evidence. The lesion's process-bearing spindle cell ("piloid") constituents fashion a densely fibrillar matrix, whereas its process-poor elements aggregate in regions of myxoid change that often progress to microcyst formation

Figure 43.65 Pilocytic Astrocytoma. Varicose Rosenthal fibers lie among the otherwise delicate and hair-like cytoplasmic processes for which the pilocytic astrocytoma is named

Figure 43.66 Pilocytic Astrocytoma. Eosinophilic granular bodies are typically associated with, although not restricted to, three indolent neuroepithelial tumors: the pilocytic astrocytoma, pleomorphic xantho- astrocytoma, and ganglioglioma

Figure 43.67 Pilomyxoid Astrocytoma. Spindled cytologic features, diffuse myxoid change, and focal perivascular pseudorosetting (center top) characterize this variant

Figure 43.68 Pleomorphic Xanthoastrocytoma. This temporo-occipital example is represented by a sharply delimited, intensely and homogenously contrast-enhancing nodule (arrow) that projects into a large cyst on postcontrast magnetic resonance imaging. Pilocytic astrocytomas and gangliogliomas may exhibit identical neuroradiological profiles and are the major differential diagnostic considerations in this setting

Figure 43.69 Pleomorphic Xanthoastrocytoma. Spindle and giant cells, including bizarre multinucleated forms, combine to give this relatively indolent neoplasm a most disturbing appearance. Note hyaline, granular, and vacuolar cytoplasmic alterations, the last attesting to lipid accumulation

Figure 43.70 Pleomorphic Xanthoastrocytoma. The immunoexpression of CD34 by tumor cells (A) and by process-bearing neural cells in adjoining, uninvolved cerebral cortex (B) is characteristic. Note the membranous quality of the immunoreactivity

Figure 43.71 Subependymal Giant Cell Astrocytoma. This postcontrast injection magnetic resonance imaging demonstrates the subependymal giant cell astrocytoma's typically intraventricular location near the foramen of Monro (with resulting obstructive hydrocephalus), as well as its characteristic circumscription. This example was not associated with other features of tuberous sclerosis

Figure 43.72 Subependymal Giant Cell Astrocytoma. Tumor cells that achieve truly giant proportions, often polygonal in contour and closely apposed in lobular array, are responsible for this neoplasm's name (but not evident in all cases). Note also the spindled elements and perivascular nuclear-free zones resembling the perivascular pseudorosettes of ependymomas

Figure 43.73 Ependymoma. The cytoplasmic processes of ependymal tumor cells condense about blood vessels to form pseudorosettes

Figure 43.74 Ependymoma. The true ependymal rosette contains a well-defined central lumen. Clustered ciliary basal bodies ("blepharoplasts") are responsible for the enhanced, granular staining of tumor cell apices

Figure 43.75 Ependymoma. Features indicative of ependymal differentia- tion at the ultrastructural level include the joining of tumor cells by elongated junctional complexes and the formation of lumens filled with microvilli and, in less number, cilia (x8800)

Figure 43.76 Ependymoma. Dot- and ring-type patterns of cytoplasmic immunolabeling for epithelial membrane antigen are diagnostically useful, though inconstant, features of this tumor group

Figure 43.77 Tanycytic Ependymoma. The fascicular pattern and long slender processes of the tanycytic ependymoma often invokes a differential diagnosis with pilocytic astrocytoma and schwannoma. Useful clues in this case included intraparenchymal location, sharp demarcation, vague pseudorosettes, strong glial fibrillary acidic protein expression, and dot-like epithelial membrane antigen positivity (not shown)

Figure 43.78 Clear Cell (RELA Fusion Positive) Ependymoma. A, The clear cell cytology and branching capillary network often suggests an oligodendroglioma, but note the sharp demarcation from adjacent brain on the right. B, Many such cases present as supratentorial masses and show RELA fusion by molecular analysis and L1CAM immunoreactivity

Figure 43.79 Anaplastic ependymoma, associated with hypercellularity, increased mitotic activity, and microvascular proliferation

Figure 43.80 Myxopapillary Ependymoma. Note the manner in which mucinous material separates draping tumor cells from a hyalinized vascular core and accumulates in rounded microcysts

Figure 43.81 Subependymoma. The huddling of small tumor cells in an expansive fibrillar meshwork is characteristic of this entity. Microcystic changes commonly round out the histologic picture

Figure 43.82 Astroblastoma. The stout and non-fibrillar cytoplasmic processes of this papillary neoplasm's constituent cells taper toward markedly hyalinized vascular cores

Figure 43.83 Chordoid Glioma of the Third Ventricle. Nests and anastomosing cords of epithelioid tumor cells arrayed against a variably myxoid stromal background typify this lesion (A), which is distinguished from other chordoid neoplasms by its diffuse cytoplasmic immunolabeling for glial fibrillary acidic protein (B). Note also in A the presence of plasma cells at upper right. These are often present in conspicuous numbers

Figure 43.84 Angiocentric Glioma. Tumor cells of monomorphous, spindled profile sheath and collar cerebrocortical blood vessels in this typical example

Figure 43.85 Choroid Plexus Papilloma. Note the characteristically bosselated surface of this surgically resected example. Deprived of its blood supply, the tumor tissue loses its normally hyperemic appearance and may assume a tan or golden hue

Figure 43.86 Choroid Plexus Papilloma. This example's delicate fibrovascular fronds are covered by an orderly, low columnar epithelium

Figure 43.87 Choroid Plexus Carcinoma. In contrast to the choroid plexus papilloma, this tumor shows anaplastic cytology and a more solid growth pattern

Figure 43.88 Ganglioglioma. The neoplastic nature of the ganglion cell tumor's large neurons is readily apparent from their cytologic abnormalities and multinucleation. Note admixed piloid astrocytic elements, microcystic architecture, and scattered eosinophilic granular bodies

Figure 43.89 Ganglioglioma. Surface perikaryal labeling for synaptophysin characterizes the neuronal elements of some ganglion cell tumors on immunohistochemistry

Figure 43.90 Ganglioglioma. Diffuse and strong cytoplasmic immuno- reactivity for chromogranin A, a feature foreign to native cerebrocortical neurons, characterizes the neoplastic neuronal perikarya of some ganglion cell tumors

Figure 43.91 Desmoplastic Infantile Ganglioglioma/Astrocytoma. As demonstrated by this example in an 8-week-old boy, tumors of the desmoplastic infantile ganglioglioma/astrocytoma group are typically large cerebral growths exhibiting dural attachment of their superficially located and contrast-enhancing solid components with the formation of prominent underlying cysts

Figure 43.92 Desmoplastic Infantile Ganglioglioma/Astrocytoma. Distinctive features include collagenized regions dominated by spindled astrocytes in fascicular or storiform array and admixed small cells of primitive appearance in nodular aggregates

Figure 43.93 Central Neurocytoma. This postcontrast magnetic reso- nance imaging shows the neurocytoma's predilection for the lateral ventricles, its tendency to be centered about the septum pellucidum, regions of bright enhancement, and associated ventriculomegaly indicative of obstructive hydrocephalus

Figure 43.94 Central Neurocytoma. The typical neurocytoma is rather densely populated by small, monomorphous cells embedded in a variably abundant, delicate fibrillar matrix. Rounded nuclear contours, perinuclear clearing, a plexiform capillary arcade, and associated microcalcifications (the basophilic structures present at upper right) impart an oligodendro- glioma-like appearance to this small cell neuronal neoplasm

Figure 43.95 Central Neurocytoma. A phenomenon restricted in the normal central nervous system to advanced stages of neuronal maturation, immunolabeling for the NeuN nuclear antigen is shared by many central neurocytomas and attests to their well-differentiated nature

Figure 43.96 Cerebellar Liponeurocytoma. A, As in central neurocytoma, tumor cells are diffusely synaptophysin immunoreactive with the exception of most lipoma-like cells. B, In contrast, the latter often express glial fibrillary acidic protein

Figure 43.97 Dysembryoplastic Neuroepithelial Tumor. A gyriform focus of increased signal attests to the largely cortical localization of this superficial lesion, seen in a FLAIR MR sequence. Also characteristic is the absence of mass effect or white matter changes indicative of edema

Figure 43.98 Dysembryoplastic Neuroepithelial Tumor. Extensive myxoid change and the disposition of small, oligodendrocyte-like cells along axonal fiber bundles and capillaries lend an alveolar or "patterned" appearance to the specific glioneuronal element of this distinctive lesion. Also present are mature neurons appearing to float in the mucoid matrix

Figure 43.99 Papillary Glioneuronal Tumor. These fields from a single tumor demonstrate papillary (A) and nonpapillary (B) components. Glial fibrillary acidic protein expression confirmed the glial nature of the former, while the latter (represented in this case by neuronal elements of "intermedi- ate" type) selectively labeled for synaptophysin. The vascular hyalinization in papillary regions (A) and bubbly, myxoid alterations in non-papillary foci (B) are common accompanying features

Figure 43.100 Rosette-Forming Glioneuronal Tumor of the Fourth Ventricle. Neurocytic rosettes of small diameter that often appear free floating (A) and that exhibit central immunolabeling for synaptophysin (B) are defining components of this entity

Figure 43.101 Diffuse Leptomeningeal Glioneuronal Tumor. This T2-weighted magnetic resonance imaging shows marked expansion of the intracranial and intraspinal subarachnoid spaces, including the basal cisterns

Figure 43.102 Diffuse Leptomeningeal Glioneuronal Tumor. A, Biopsy typically reveals a markedly expanded leptomeningeal layer with tumor cells resembling oligodendroglioma. Immunohistochemistry often reveals strong OLIG2 (B) and patchy synaptophysin (C) expression

Figure 43.103 Multinodular and vacuolating neuronal tumor with pale nodules (A) composed of variably vacuolated neuronal cells (B)

Figure 43.104 Hypothalamic Hamartoma. T1-weighted magnetic resonance image showing sessile hypothalamic mass (arrow)

Figure 43.105 Hypothalamic Hamartoma. A, This example was composed of mildly disorganized gray matter composed predominantly of small neurocytic or oligodendrocyte-like neurons. B, Their neuronal lineage was confirmed on a Neu-N immunostain

Figure 43.106 Dysplastic Gangliocytoma (Lhermitte-Duclos Disease). T2-weighted magnetic resonance imaging reveals the typical "tiger-stripe" pattern in the right cerebellar cortex

Figure 43.107 Dysplastic Gangliocytoma (Lhermitte-Duclos Disease). This resection specimen reveals replacement of the internal granular layer by large dysmorphic ganglion cells. Note scattered retained internal granular cell neurocytes in lower portion of figure

Figure 43.108 Medulloblastoma (Classic and WNT-Activated Sub- types). A, The classic medulloblastoma is a highly cellular neoplasm composed of diminutive, undifferentiated-looking elements possessed of little definable cytoplasm and prone to nuclear molding. B, A subset of classic medulloblastomas show evidence of WNT pathway activation, most often detected by the presence of nuclear ẞ-catenin immunoreactivity

Figure 43.109 Medulloblastoma (Desmoplastic/Nodular and SHH- Activated Subtypes). A, Micronodular zones of reduced cellularity ("pale islands") are a striking feature of this medulloblastoma variant. B, Virtually all desmoplastic/nodular (and a smaller subset of classic) medulloblastomas show evidence of SHH pathway activation, including immunoreactivity to GAB1, often with strongest expression in the internodular regions. C, A poor prognosis subtype of SHH-activated medulloblastoma features p53 overexpression, often with superimposed anaplastic cytology

Figure 43.110 Medulloblastoma. Homer Wright rosettes consist of tumor cell nuclei disposed in circular fashion about tangled cytoplasmic processes. These structures are indicative of differentiation along neuronal lines

Figure 43.111 Medulloblastoma With Extensive Nodularity. This variant of medulloblastoma is typified by the linear streaming of rounded, "neurocytic" tumor cell nuclei within amassed cytoplasmic processes

Figure 43.112 Large Cell/Anaplastic Medulloblastoma. Cellular enlargement, often prominent nucleoli, and pronounced mitotic and apoptotic activity are features of this virulent medulloblastoma subtype

Figure 43.113 Embryonal Tumor With Multilayered Rosettes. A, Typical of the subtype with abundant neuropil and true rosettes is a delicate fibrillar matrix in which primitive neuroepithelial elements and ependymoblastic rosettes (center) are arrayed, the latter having well-defined (though often minute) lumens and being composed of mitotically active tumor cells with granular apical stippling. B, Immunoreactivity for LIN28 is diagnostically useful, regardless of whether the tumor resembles embryonal tumor with abundant neuropil and true rosettes, ependymo- blastoma, or medulloepithelioma

Figure 43.114 Medulloepithelioma. A tubulopapillary disposition of its columnar elements characterizes this primitive neuroepithelial neoplasm

Figure 43.115 Atypical Teratoid/Rhabdoid Tumor. A, Neoplasms of this family typically contain at least some cells of large, rhabdoid phenotype. A second example (B) harbors, at right, small cell elements of primitive neuroepithelial appearance and a differentiated glandular structure, at left, embedded in a neoplastic component of mesenchymal appearance

Figure 43.116 Atypical Teratoid/Rhabdoid Tumor. Loss of nuclear INI1 protein expression on immunohistochemical study characterizes this entity. Note retained expression by endothelial cells and perivascular mononuclear cell infiltrate

Figure 43.117 Pineocytoma. Shown here are the conspicuous rosettes that constitute a defining feature of this neoplasm. Note the benign oligodendroglioma-like/neurocytoma-like nuclear features, monomorphism, and absence of mitotic activity

Figure 43.118 Pineal Parenchymal Tumor of Intermediate Differentia- tion. Note the sheet-like architecture, hypercellularity, lack of pineocytic rosettes, and increased mitotic activity, but the features fall short of the primitive "small blue cell" cytology seen in pineoblastoma

Figure 43.119 Papillary Tumor of the Pineal Region. Perivascular structuring (A) and strong immunoexpression of CK18 (B) typify the cellular elements of this lesion

Figure 43.120 Meningioma. Circumscription, homogeneous contrast enhancement and anchorage to the dura (in this case, the tentorium) typify the meningioma. This magnetic resonance imaging also demonstrates thickened and abnormally enhancing dural "tails" extending from the lesional borders-a finding suggestive, though not diagnostic, of this tumor entity

Figure 43.121 Meningioma. The broad dural base depicted here is characteristic

Figure 43.122 Meningioma. Indistinct cytoplasmic boundaries, nuclear clearing ("pseudoinclusions"), cellular whorls, and a psammoma body are all apparent in this view of a meningotheliomatous (syncytial) meningioma

Figure 43.123 Meningioma. Cellular spindling and a fascicular or storiform architecture are evidenced by meningiomas of "fibroblastic" type

Figure 43.124 Microcystic Meningioma. The wispy "cobweb-like" pattern results from extracellular fluid accumulation and characterizes this variant

Figure 43.125 Secretory Meningioma. This variant of meningothelio- matous meningioma harbors eosinophilic globules (A) that label with antibodies to carcinoembryonic antigen (B)

Figure 43.126 Lymphoplasmacyte-Rich Meningioma. The brisk inflammatory infiltrate in this case partially obscures the underlying meningioma (A), the latter of which is highlighted by an immunostain for somatostatin receptor 2a (B)

Figure 43.127 Chordoid Meningioma. A, The ribbon-like architecture, vacuolated cytoplasm, and alcian blue-positive mucinous stroma provides a remarkable resemblance to chordoma of the bone. B, However, these tumors express the same immunomarkers as conventional meningiomas, often including progesterone receptor

Figure 43.128 Angiomatous (Vascular) Meningioma. The marked hypervascularity (often with hyalinization) and degenerative nuclear atypia may obscure the meningothelial nature of this variant

Figure 43.129 Clear Cell Meningioma. The example shown here arose from the filum terminale of a 9-year-old girl. Note cytoplasmic clearing, traversing collagenous bands, and absence of meningothelial-type whorls

Figure 43.130 Rhabdoid Meningioma. Rhabdoid features include loss of cohesion, large eccentrically placed vesicular nuclei, macronucleoli, and a paranuclear fibrillar to globular eosinophilic inclusion (A), which is often further highlighted on vimentin immunohistochemistry (B)

Figure 43.131 Papillary Meningioma. This intraspinal example, which also exhibited features of an atypical meningotheliomatous meningioma with increased mitotic activity and foci of necrosis (not shown here), metastasized to lung, lymph node, and bone

Figure 43.132 Meningioma. Cytoplasmic labeling for epithelial membrane antigen on immunoperoxidase assay, depicted here, characterizes the overwhelming majority of meningiomas, regardless of their histologic subtype

Figure 43.133 Atypical Meningioma. Low-magnification clues include two-dimensional sheeting architecture (loss of whorling and fascicles) and small cell formation (clusters of tumor cells with high N/C ratio) (A), as well as spontaneous (e.g. not embolization-induced) necrosis (B)

Figure 43.134 Atypical Meningioma. Another criterion for atypical meningioma in the WHO 2016 scheme is brain invasion, characterized by tongue-like protrusions into adjacent gliotic brain (A), which can be further verified using glial fibrillary acidic protein immunohistochemistry (B)

Figure 43.135 Anaplastic Meningioma. A, On postcontrast magnetic resonance imaging, this tumor was large, had irregular borders with adjacent brain, and displayed central areas of low signal intensity cor- responding to foci of necrosis. Histologically, there was extensive geo- graphic necrosis (B), a mitotic index over 20 per 10 high-power fields (not shown), and a Ki-67 labeling index greater than 20% (C)

 Figure 43.136 Solitary Fibrous Tumor/Hemangiopericytoma, WHO Grade I. A, Demonstrating the classic solitary fibrous tumor histology, this tumor is predominantly spindled and shows lace-like brightly eosino- philic intercellular collagen. Immunohistochemistry reveals diffuse CD34 (B) and nuclear STAT6 (C) positivity

Figure 43.137 Solitary Fibrous Tumor/Hemangiopericytoma, WHO Grade III. In comparison to the case in Fig. 43.136, this one is more cellular, less collagenized, and includes greater than 5 mitoses/10 hpf (A and B). Note also the typical hypervascularity, including gaping thin walled blood vessels (A). Immunohistochemically, CD34 highlighted the rich vascularity but was negative in tumor cells (not shown), while STAT6 was diffusely expressed in tumor nuclei (C)

Figure 43.138 Primary Central Nervous System Lymphoma. As demonstrated in this postcontrast injection magnetic resonance imaging, primary cerebral lymphomas exhibit a predilection for the deep, para- ventricular white matter and tend to striking and fairly homogeneous enhancement in "sporadic" (as opposed to AIDS-related) cases

Figure 43.139 Primary Central Nervous System (CNS) Lymphoma. Although not apparent in all cases, a vasocentric growth pattern with tumoral infiltration of blood vessel walls and Virchow-Robin spaces is common to primary CNS lymphomas. Systemic lymphomas secondarily involving the neuroparenchyma may also preferentially grow in this fashion

Figure 43.140 Primary Central Nervous System (CNS) Lymphoma. An intraoperative smear preparation demonstrates the large cell cytology and nuclear features characteristic of CNS lymphoma. The lack of cellular cohesion or cytoplasmic processes, respectively, are useful in discriminating this tumor from metastatic carcinoma and glioblastoma multiforme, two neoplasms that commonly enter the clinical differential diagnosis

Figure 43.141 Primary Central Nervous System (CNS) Lymphoma. The great majority of lymphomas arising in the CNS are of B-cell type and, as shown here, label for CD20 on immunoperoxidase (L-26) assay

Figure 43.142 Intravascular Large B-Cell Lymphoma. Large, highly atypical cells fill a small blood vessel in the white matter of a 63-year-old woman subjected to brain biopsy for progressive cognitive impairment. Positive immunoassays for leukocyte common antigen and CD20 confirmed their lymphoid nature and B-cell phenotype, respectively

Figure 43.143 Meningeal Melanocytoma. The tendency to cellular whorling manifested by this example, resected from the cervical region of a 34-year-old man with a protracted history of neck pain and gait disturbance, accounts for the potential misclassification of melanocytomas as melanotic meningiomas. Note finely divided brown pigment in the cytoplasm of some tumor cells (as opposed to coarse pigment granules in melanophages), delicate and monomorphous nuclear features, lack of mitotic activity, and absence of necrosis

Figure 43.144 Hemangioblastoma. Most hemangioblastomas arise in the cerebellar hemispheres, where, as emphasized in this postcontrast injection magnetic resonance imaging, they present as diminutive, brightly enhancing, and sharply delimited mural nodules projecting into sizable cysts

Figure 43.145 Hemangioblastoma. The neoplasm's defining "stromal" cells are most readily visualized when lipid accumulation imparts a foamy or vacuolated quality to their pale cytoplasm

Figure 43.146 Metastatic Carcinoma. A cohesive growth pattern and clearly delimited tumor-central nervous system interface are hallmarks of neoplasms metastatic to the brain. The adenocarcinoma (right), derived from a primary in the left lung, "pushes" against adjacent cerebral white matter

Figure 43.147 Metastatic Carcinoma. The cellular cohesion characteristic of most epithelial neoplasms and foreign to gliomas and lymphomas is generally maintained in cytology preparations, facilitating rapid intraoperative diagnosis. Note also the absence of cytoplasmic processes and presence of conspicuous nucleoli, the latter also alien to most neuroepithelial tumors, in this smear preparation of a poorly differentiated pulmonary adenocar- cinoma that presented as a solitary, right frontal lobe brain mass