A 7-year-old male presents with headache, vomiting and gait ataxia. A noncontrast head CT shows a hyperdense mass in the posterior fossa. A biopsy is performed, and a representative section is shown here. What is the most likely diagnosis?

What is the most likely diagnosis?

A. Astrocytoma
B. Glioblastoma
C. Oligodendroglioma
D. Medulloblastoma
E. Ependymoma

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(Scroll down for the answer)

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The diagnosis in this case is medulloblastoma. Medulloblastoma is most common in the pediatric age group, in which it accounts for 30% of all brain tumors. Most commonly found in the cerebellum, it usually presents with symptoms of increased intracranial pressure, such as nausea and vomiting. Some patients present with cerebellar symptoms such as gait ataxia.

Histologically, medulloblastoma is composed of sheets of densely-packed, small, dark, anaplastic cells. Sometimes, the cells form little rosettes, called Homer-Wright rosettes (there are a bunch of these in the image above, especially in the lower half).

Although highly malignant, medulloblastoma is fortunately very radiosensitive, and with complete excision and radiation, 5 year prognosis is approximately 75%.

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