A 9-year-old boy presents with morning headache, vomiting, and truncal ataxia. MRI reveals a midline posterior fossa mass arising from the cerebellar vermis, homogeneously enhancing, with hydrocephalus. Histology shows a small round blue cell tumor with Homer Wright rosettes. Which molecular subgroup has the best prognosis?

• A WNT-activated ✓
• B SHH-activated
• C Group 3
• D Group 4

Explanation

This describes medulloblastoma, the most common malignant brain tumor of childhood. Medulloblastoma is divided into four molecular subgroups: WNT, SHH, Group 3, and Group 4. WNT-activated medulloblastoma has the best prognosis with over 90% long-term survival. Group 3 has the worst prognosis, often presenting with metastatic disease. The distinction is emphasized in the WHO 2021 CNS classification and is high-yield for exams.

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.