Medulloblastoma (WHO Grade IV)

General: Malignant embryonal tumor of the cerebellum, most common in children (~70% < 16yo), with predominantly neural differentiation. Tends to metastasize via cerebrospinal fluid; ~33% of patients present with metastases. Most (~75%) arise in the vermis and extend into the fourth ventricle.

Imaging:

• CT/MRI: Solid, intense & homogeneously contrast-enhancing masses. CNS metastases seen as foci of nodular or diffuse contrast enhancement in the leptomeninges or ventricular surfaces.

Gross: Variable texture & degree of circumscription. A few are massively hemorrhagic.

Microscopic: Classically, densely packed cells with round-to-oval or carrot-shaped hyperchromatic nuclei with scanty cytoplasm. Rosettes are typical but not required. Occasional ganglion cells are seen. Mitoses and apoptosis usually common. Geographic necrosis uncommon, but pseudopalisading necrosis possible. Occasional giant cells +/- multinucleation. Rare vascular proliferation, calcification, or massive hemorrhage. Histologic types include:

• Desmoplastic medulloblastoma:
• Medulloblastoma with extensive nodularity and advanced neuronal differentiation:
• Large cell medulloblastoma:

Differential Diagnosis:

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

((())) WHO 2000.

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