What Are Carrot Shaped Brain Tumors

FIGURE 1.11 WHO grades II and III ependymoma. The typical low-grade tumor is densely cellular and composed of oval to carrot-shaped cells, with dense speckled nuclei and tapering eosinophilic cytoplasm (11A; H&E @ 200x). Note the ependymal perivascular psuedorosette in the center of the field. The anaplastic ependymoma is more pleomorphic and demonstrates mitotic activity (11B; H&E @ 400x). See Plate 1.11 in Color Plate Section.

composed of oval to carrot-shaped cells, with a dense speckled nucleus and tapering eosinophilic cytoplasm (see Fig. 1.11) [46]. Some tumors have cells with a more glial appearance and more background fibrillar-ity or more epithelioid cells and architecture. Perivas-cular pseudorosettes, which are commonly observed, are circular arrangements of tumor cells that send processes towards vessel walls, creating a perivascu-lar ''nuclear-free zone'' that can be noted at low-power. Less commonly, true ependymal rosettes, surrounding a true lumen, can be observed. Ependymomas are usually GFAP positive. Anaplastic ependymomas (WHO grade III) have additional features such as increased cellularity, mitotic activity, pleomorphic nuclei, vascular hyperplasia, nuclear atypia, and necrosis. Myxopapillary ependymomas are WHO grade I tumors that arise in the lower spine within the cauda equina. They display an admixture of fibrillated and epithelioid cells with an exuberant connective tissue stroma. Papillary arrangements of elongated fibrillary cells that extend delicate processes to hyalinized vessels are prominent. In addition, prominent myxoid degeneration of the cell cytoplasm and blood vessel walls is a constant feature. Subependymomas are WHO grade I tumors that develop in the walls of the ventricular system (65-70 per cent fourth ventricle) and may present with hydrocephalus. They are composed of tumor cells exhibiting features of ependymal and astrocytic differentiation, with the tendency to form distinct clusters (''glomerate'' structures) separated by cellfree areas.

Choroid Plexus Tumors. Neoplasms of the choroid plexus are classified by the WHO as choroid plexus papillomas (WHO grade I) or choroid plexus carcinomas (WHO grade III) [24,25,30]. These tumors arise from the specialized epithelium constituting the choroid plexus and therefore develop within the lateral and fourth ventricles. Choroid plexus papillomas are usually diagnosed in children and present with increased intracranial pressure from hydrocephalus secondary to obstruction of cerebrospinal fluid (CSF) pathways or overproduction of CSF. Histological examination reveals delicate fibrovascular connective tissue fronds covered by a single layer of uniform cuboidal to columnar epithelial cells [47]. The fronds are similar in appearance to normal choroid plexus, but with slightly more cellularity and pleomorphism. Choroid plexus carcinoma has additional features of anaplasia including increased cellularity, frequent mitoses, cellular and nuclear pleomorphism, loss of papillary structure, regional brain invasion, and areas of necrosis.

Neuronal and Mixed Neuronal-Glial Tumors. Neuronal and mixed neuronal-glial tumors are a heterogeneous group of neoplasms that are mainly classified by the WHO as grades I and II (see Table 1.7) [24,25,30]. Gangliogliomas are well differentiated, slow-growing tumors with a mixture of neoplastic glial and neuronal elements. They are composed of irregular groups of large, multipolar neurons with dysplastic features, and intermixed with regions of neoplastic glial cells, usually of astrocytic origin (WHO grade I or II; see Fig. 1.12) [48]. The astrocytic

TABLE 1.7 WHO Classification: Neuronal and Mixed Neuronal-Glial Tumors

Gangliocytoma

Dysplastic gangliocytoma of cerebellum (Lhermitte-Duclos)

Desmoplastic infantile

Astrocytoma/ganglioglioma

Dysembryoplastic neuroepithelial tumor

Ganglioglioma

Anaplastic ganglioglioma

Central neurocytoma

Cerebellar liponeurocytoma

Paraganglioma of the filum terminale

Glial Cells The Brain
FIGURE 1.12 WHO grade II ganglioglioma. The tumor demonstrates a mixture of large neoplastic ganglion cells within a background of diffuse, low-grade fibrillary astrocyoma. H&E @ 400x. See Plate 1.12 in Color Plate Section.
What Color Are Tumors
FIGURE 1.13 Central neurocytoma. Note the presence of dense sheets of uniform round cells with neuronal features and the delicate vasculature. H&E @ 200x. See Plate 1.13 in Color Plate Section.

portion is fibrillary and similar to low-grade astrocytomas as described earlier. Eosinophilic granular bodies are often noted, along with frequent peri-vascular lymphocytic infiltration. Occasional mitoses may be present, but significant pleomorphism, necrosis, and vascular hyperplasia are absent. Anaplastic ganglioglioma (WHO grade III or IV) are similar to low-grade gangliogliomas, except for additional malignant features within the glial component of the tumor [30,48]. These malignant features include increased cellularity, frequent mitoses, nuclear pleo-morphism and atypia, regional brain invasion, and areas of necrosis. Gangliocytomas are well differentiated, slow-growing tumors composed of neoplastic, mature ganglion cells, without a glial component. The ganglion cells are large and multipolar, and often show dysplastic features. There is a non-neoplastic glial stroma and network of reticulin fibers that surround the ganglion cells.

Central neurocytomas are low-grade tumors (WHO grade II) composed of uniform cells with neuronal differentiation that arise in the lateral ventricles near the foramen of Monro [24,25,30]. Histological examination reveals sheets of uniform round cells with neuronal features, along with fibrillary areas that mimick neuropil (see Fig. 1.13) [30,49]. In some tumors, regions with oligodendroglioma-like features may be noted, with a honeycomb appearance and large fibrillary areas. The tumors stain diffusely with synaptophysin, neuron specific enolase, and calcineurin.

Pineal Parenchymal Tumors. The WHO recognizes three forms of pineal parenchymal tumors, including the pineocytoma (WHO grade II), pineoblastoma (WHO grade IV), and tumors of intermediate differentiation [24,25,30]. The pineocytoma is a slow-growing pineal tumor that usually occurs in young adults. On histological examination, the tumor is a well-differentiated neoplasm composed of sheets of small, uniform, mature cells resembling pineocytes. A lobular pattern may be present, with groups of tumor cells separated by mesenchymal septae. The cells are small in size, with inconspicuous nucleoli, a fine chromatin pattern, and moderate quantities of eosinophilic cytoplasm. Another characteristic feature is the presence of pineocytomatous rosettes, which can vary in size and number. Mitoses and regions of necrosis are either absent or rare. Pineoblastomas are malignant tumors with a more aggressive growth rate, tendency to invade surrounding brain, and disseminate along CSF pathways. They are composed of patternless sheets of densely packed small blue cells with round-to-irregular nuclei and scant cytoplasm, similar to other small cell tumors

Homer Wright Rosettes
FIGURE 1.14 WHO grade IV pineoblastoma. Densely cellular neoplasm with large, pleomorphic and hyperchromatic nuclei. Cells forming Homer-Wright rosettes are present. H&E @ 400x. See Plate 1.14 in Color Plate Section.
High Grade Large Cell Malignancy
FIGURE 1.15 WHO grade IV medulloblastoma. Note the dense cellularity and presence of undifferentiated cells with hyper-chromatic, oval to carrot-shaped nuclei with scant cytoplasm. The nuclei have a tendency to mold against one another. H&E @ 200x. See Plate 1.15 in Color Plate Section.

TABLE 1.8 WHO Classification: Embryonal Tumors

Medulloepithelioma Ependymoblastoma Medulloblastoma

Desmoplastic medulloblastoma Large-cell medulloblastoma Medullomyoblastoma Melanotic medulloblastoma Supratentorial PNET Neuroblastoma Ganglioneuroblastoma Atypical teratoid/rhabdoid tumor

(i.e., primitive neuroectodermal tumors, PNET; see Fig. 1.14). The tumor cells have a high nuclear cytoplasmic ratio, hyperchromatic nuclei, and indistinct cell borders. Typical pineocytomatous rosettes of lower-grade pineal tumors are absent. However, Homer-Wright pseudo-rosettes may be noted. Mitotic activity is variable and can be high in some tumors. Regions of necrosis are commonly noted.

Medulloblastoma and other Embryonal Tumors. Embryonal tumors are a group of aggressive, malignant neoplasms that usually affect children that are classified by the WHO as grade IV in all cases (see Table 1.8) [24,25,30]. All embryonal tumors share the common features of high cellularity, frequent mitoses, regions of necrosis, and a propensity for metastases along CSF pathways. Medulloblastoma is the most common of the embryonal tumors and is considered a PNET of the cerebellum. It usually arises in the midline in children, within the cerebellar vermis, while in adults it is more likely to have an off-center location within the cerebellar hemispheres. The typical medulloblastoma is densely cellular and composed of undifferentiated cells with hyperchro-matic, oval to carrot-shaped nuclei with scant cytoplasm (see Fig. 1.15) [30,50]. The nuclei have a tendency to mold against one another. Mitoses and single-cell necrosis are frequently present. Evidence of anaplasia is variable and may include increased nuclear size, abundant mitoses, and the presence of large-cell or similar aggressive cellular morphology. Some tumors may display immunohistochemical and morphological evidence for differentiation along neuronal, glial, or mesenchymal lines. Tumors with neuronal differentiation may display mature ganglion cells, immunoreactivity for neuronal markers (e.g., synaptophysin), neuroblastic Homer Wright rosettes, and ultrastructural findings such as dense core granules and synaptic vesicles. Several histologic variants of medulloblastoma are recognized by the WHO including the desmoplastic, large cell, and melanotic sub-types, as well as medullomyoblastoma. The desmoplastic variant shows nodular, reticulin-free zones (''pale islands'') surrounded by densely packed, highly proliferative cells within a dense reticulin fiber network. Large-cell medulloblastoma is an uncommon variant with large cells that contain large, rounded nuclei with prominent nucleoli and more abundant cytoplasm. Nuclear molding is less frequent; however, mitotic activity, pleomorphism, and necrosis are more prominent. Melanotic medullo-blastoma has similar histological features to more typical cases, except for the presence of melanotic tumor cells that often form tubular epithelial structures. Medulloblastomas are highly proliferative tumors, with Ki-67 labeling indices ranging from 15 to 50 per cent.

Atypical teratoid/rhabdoid tumors (WHO grade IV) are rare neoplasms that usually develop in the posterior fossa and affect children less than 3 years of age [24,25,30]. Histological examination reveals a cellular tumor with large and polygonal rhabdoid cells with conspicuous eosinophilic or pink cytoplasm, that contain spherical fibrillary intracytoplas-mic inclusions composed of bundles of intermediate filaments [51]. Other tissue elements may be present, such as primitive neuroepithelium, mesenchyme, and mature epithelium. Mitoses and regions of necrosis are common. The rhabdoid cells lack true muscle differentiation and do not react positively with desmin. They may show variable reactivity with epithelial-membrane antigen, vimentin, smooth muscle actin, and GFAP. These tumors have marked proliferative capacity as shown by Ki-67 studies, with labeling indices ranging from 50 to 80 per cent. Molecular studies consistently reveal a loss of chromosome 22 or specific loss of 22q11, with mutations in the chromatin remodeling tumor suppressor gene hSNF5/INI1 (human sucrose nonfermentor/integrase interactor 1). This molecular signature is unique to teratoid/rhabdoid tumors and is not present in medulloblastomas or other embryonal tumors.

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  • mantissa
    What are carrot shaped brain tumors?
    5 years ago
  • J Lowe
    What is the shape of a carrot cell?
    4 years ago

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