Hemangioblastoma is a tumor that occurs most commonly in the cerebellum.
There is usually a nodule of tumor associated with a cyst. These tumors,
whether benign (usual) or malignant (rarer), may cause clinically
significant problems, for example angiomas in the brain or spinal cord may
press on nerve or brain tissue. As an angiomas grows, the walls of the blood
vessels may weaken and leak, causing damage to surrounding tissues. Blood
leakage from angiomas in the retina can interfere with vision.