Medulloblastoma Grade

This most important malignant tumor in children constitutes 16% to 20% of intracranial childhood tumors. In adults, it is rare. Situated in the cerebellum, it may arise from remnant cells of the external granular layer of the cortex, from embryonal cell nests in the superior medullary velum, or from subependymal matrix cells of the fourth ventricle. Familial occurrences (twins and siblings), coexistence with other brain tumors, and visceral malignancies and malformations are documented.

Medulloblastoma manifests with truncal ataxia and broad-based gait. Being fast-growing in the posterior fossa, it produces increased ICP, with headache, vomiting, and papilledema early in its clinical course. The tumor is inhomogeneously hyperintense on T2-weighted images and enhances with gadolinium on Tl-weighted images. Postoperative survival averages 5 years.

Grossly, medulloblastoma is preferentially situated in the cerebellar vermis, extending into the fourth ven tricle; less often into the hemispheres. Poorly demarcated, it is pinkish-gray and soft.

Histologically, medulloblastoma is densely cellular and composed of small cells with round, oval, or carrot-shaped hyperchromatic nuclei surrounded by scanty cytoplasm (blue cell tumor). The cytologic pattern varies from clusters separated by fine fibrovascular stroma, through pseudopalisading around necrosis, to pseudorosette formation. Mitotic activity is often high and apoptotic figures may be numerous. Medulloblasts may differentiate into neurons and glial cells. Neuronal differentiation is evidenced by immunoreactivity of tumor cells for neuron-specific enolase and synaptophysin. Glial differentiation is supported by the presence of GFAP-positive tumor cells. Necrosis, small cysts, and calcifications occasionally occur. Medulloblastoma may disseminate via CSF pathway to form small nodules and diffuse infiltrates in the ventricular wall and subarach-noid space (Fig. 11.25).

Genetic alterations include isochromosome 17q; losses of chromosomes 6q, 9q, 10q, 11, and 16q; trisomy-1q; and mutations of TP53 occur in a small number of tumors.

Histological Variants

Nodular medulloblastoma refers to the presence of "pale islands," consisting of tumor cells that display small nuclei, abundant cytoplasm, and a tendency to figure 1 1.25

Medulloblastoma. A. Midsagittal section of the cerebellum shows a large tumor arising from the vermis and filling the lumen of the fourth ventricle. Small tumor nodules are present in the cerebellar cortex, indicating dissemination via CSF (cresyl violet). B. Highly cellular tumor consists of anaplastic cells with small round to oval hyperchro-matic nuclei surrounded by scanty cytoplasm (HE). C. Pale island in nodular variant (HE). D. A desmoplastic variant in the cer-ebellar hemisphere (cresyl violet).

figure 1 1.25

Medulloblastoma. A. Midsagittal section of the cerebellum shows a large tumor arising from the vermis and filling the lumen of the fourth ventricle. Small tumor nodules are present in the cerebellar cortex, indicating dissemination via CSF (cresyl violet). B. Highly cellular tumor consists of anaplastic cells with small round to oval hyperchro-matic nuclei surrounded by scanty cytoplasm (HE). C. Pale island in nodular variant (HE). D. A desmoplastic variant in the cer-ebellar hemisphere (cresyl violet).

differentiate along neuronal line. This histologic pattern seems to be less aggressive and correlates with a longer survival.

Large cell/anaplastic medulloblastomas contain cells with large vesicular nuclei and pleomorphic ana-plastic cells. Mitoses and apoptotic bodies are numerous. This histologic pattern seems to be more aggressive and correlates with shorter survival.

Desmoplastic medulloblastoma develops in the cer-ebellar hemispheres of children and young adults. His-tologically, clusters of tumor cells are separated by a rich reticulin and collagenous network (see Fig. 11.25).

Medullomyoblastoma, lipomatous, and melanotic medulloblastomas contain striated muscle fibers, lipid cells, and melanotic cells, respectively.

101 Power Tips For Preventing and Treating Headaches

101 Power Tips For Preventing and Treating Headaches

Are you fed up with your frequent headache pain? 101 Simple Ways to Attack Your Headache BEFORE the Pain Starts Guaranteed No Pain, No Fear, Full Control Normal Life Again Headaches can stop you from doing all the things you love. Seeing friends, playing with the kids... even trying to watch your favorite television shows.

Get My Free Ebook


Post a comment