Hemangioblastoma

A 43 x 36 x 31 mm mass arises from the cerebellar vermis and extends more to the left than the right. Superiorly it abuts the left tentorium cerebelli. There is associated mass-effect with compression of the fourth ventricle and the aqueduct so that there is acute hydrocephalus with trans-ependymal edema. There is flattening of the pons and extension of the cerebral tonsils into the foramen magnum.

The lesion is heterogeneous in signal intensity with multiple cystic or necrotic areas; the larger superior portion of the lesion is predominately solid, with rim enhancing cystic component inferiorly. The solid components enhance fairly homogeneously. Along the posterior margin of the lesion there are multiple flow voids indicating that the lesion is vascular. Although broadly abutting the tentorium cerebelli, there is no dural tail of enhancement or diffusion restriction.  Small volume of perilesional T2 hyperintensity extending into the left middle cerebellar peduncle.

Scattered T2 hyperintense foci noted in cerebral white matter. No further enhancing lesion.

Conclusion:

Vascular tumor arising from the cerebellar vermis with severe posterior fossa mass effect and hydrocephalus. Differential include hemangioblastoma and vascular metastasis. Given the size and broad abutment of tentorium, but less likely possibility is a large atypical meningioma or hemangiopericytoma severely indenting the posterior aspect of the cerebellum.

MICROSCOPIC DESCRIPTION:

Sections of the cerebellum show a moderately cellular tumor with scattered stromal cells in a background of many blood vessels of varying sizes. The tumor cells form aggregates. They have enlarged nuclei with hyperchromasia and foamy vacuolated cytoplasm. Mitoses are inconspicuous. There is no necrosis. The tumor cells are focally inhibin positive. CAM5.2 is negative. The features are those of hemangioblastoma. There is no evidence of metastatic carcinoma. 

FINAL DIAGNOSIS: Hemangioblastoma (WHO Grade I).