von Hippel Lindau disease - multiple hemangioblastomas

At least five heterogeneous but predominantly T2 hyperintense and enhancing intra-axial lesions are present within the posterior fossa, the largest within the left inferior cerebellar hemisphere measuring 2.7 x 2.5 cm in transaxial diameter. 2 further punctate foci of enhancement in the right cerebellar hemisphere are suspicious for additional tiny lesions. 

Most of these abut the pial surface and have enlarged supplying and draining vessels adjacent. Edema and positive mass effect  associated with the largest lesion, resulting in the distortion of the inferior mid brain, pons and fourth ventricle. Up to 13mm inferior tonsillar herniation. Moderated hydrocephalus with minor periventricular T2 hyperintensity. No further supratentorial abnormality, in particular no other intra-axial mass nor abnormal areas of enhancement.

The larger and more anterior left cerebellar hemisphere lesion is markedly hypervascular, with supply from enlarged left anterior inferior cerebellar arteries, as well as posterior inferior cerebellar arteries. No
significant meningeal supply. Other smaller lesions are identified, the larger superior to the 25mm lesion, and better characterized on MRI. No supply from external carotid branches.

The sections show replacement of cerebellar parenchyma by a moderately hypercellular, intensely vascular tumor.  Vascular channels vary from large caliber thin-walled sinusoids to small capillaries.  These are lined by unremarkable endothelial cells.

Intervening tumor is composed of lobules and diffuse sheets of stromal cells with round and oval vesicular nuclei and a variable amount of pale and granular cytoplasm.  No mitotic figures are identified and there is no vascular endothelial cell hyperplasia and no necrosis.  The features are of a capillary hemangioblastoma.

DIAGNOSIS: Posterior fossa capillary hemangioblastoma (WHO Grade I)