Cerebellum, Hemangioblastoma

Hemangioblastoma is a WHO grade 1 CNS neoplasm of uncertain etiology. It presents clinically with local mass effect with most common sites of involvement including the cerebellum and brainstem. Germline mutation in VHL gene has been associated with 10% of cases, with most sporadic tumors showing inactivated VHL gene. Grossly on cut surface, the lesion is nodular-cystic with yellow-red (fatty, vascularized) appearance. Microscopic examination demonstrates a well-circumscribed nodule with solid component showing areas of high and low cellularity, gaping vessels, and cystic changes which imparts the variegated appearance of hemangioblastoma. The tumor has a vague organoid architecture due to the elaborate vascular network and surrounding polygonal stromal cells with hyperchromatic nuclei and vacuolated cytoplasm. Focal findings of hyaline globules are identified but are non-specific since can be found in other CNS tumors. Immunohistochemically the stromal or interstitial tumor cells stain focally positive for inhibin-a, focally stain positive for GFAP, and negative for EMA. The highly vascularized component stains positive for CD34/31. Differential diagnosis includes metastatic renal cell carcinoma, which is also associated with VHL syndrome (positive EMA, negative inhibin-a) and other primary CNS tumors.