A 12-year-old boy has a posterior fossa tumor. Biopsy shows Homer Wright rosettes and small round blue cells in a background of neuropil. The diagnosis is:
- A Ependymoma
- B Medulloblastoma (PNET) ✓
- C Craniopharyngioma
- D Pilocytic astrocytoma
Correct answer: B. Medulloblastoma (PNET)
Explanation
Medulloblastoma (WHO grade 4) is the most common malignant brain tumor in children, arising from the cerebellum/posterior fossa. Histologically, Homer Wright rosettes (tumor cells surrounding a central tangle of neuropil without a central lumen) and sheets of small round blue cells (primitive neuroectodermal cells) are characteristic. Ependymoma shows perivascular pseudorosettes. Craniopharyngioma has calcification and cholesterol crystals. Pilocytic astrocytoma is a low-grade glioma.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.