A 5-year-old boy presents with morning headaches and vomiting. MRI shows a midline cerebellar mass filling the fourth ventricle with leptomeningeal enhancement along the spinal cord. Histology shows small round blue cells arranged in Homer Wright rosettes. The most likely diagnosis is:

• A Pilocytic astrocytoma
• B Ependymoma
• C Medulloblastoma ✓
• D Choroid plexus papilloma

Explanation

Medulloblastoma is a primitive neuroectodermal tumor of the cerebellum, typically arising in the vermis of children and presenting with raised intracranial pressure from fourth ventricle obstruction. It shows small round blue cells with Homer Wright rosettes and spreads via CSF with drop metastases to the spinal cord. Pilocytic astrocytoma is cystic with Rosenthal fibers, ependymoma shows perivascular pseudorosettes, and choroid plexus papilloma arises in the lateral ventricle of young children.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.