A 40-year-old man has a well-circumscribed cerebellar tumor. Histology shows biphasic pattern with compact Rosenthal fiber–rich areas and loose microcystic areas. The tumor is GFAP positive and WHO grade 1. What is the diagnosis?

• A Diffuse astrocytoma
• B Ependymoma
• C Medulloblastoma
• D Pilocytic astrocytoma ✓

Explanation

Pilocytic astrocytoma is a WHO grade 1 glioma characterized by a biphasic pattern — alternating compact, bipolar (hair-like) cells with Rosenthal fibers and loose microcystic areas with multipolar cells. GFAP positivity confirms glial lineage. It is the most common pediatric brain tumor and also occurs in young adults, typically in the cerebellum, with KIAA1549-BRAF fusion being the hallmark molecular alteration.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.