Radiological images and intraoperative photographs showing a thrombosed giant distal PICA aneurysm simulating large cavernous angioma. A CT scan shows a 2.5 cm sized hemorrhagic mass lesion with rim calcification in left cerebellar hemisphere (upper left). Aneurysmal dilatation is not seen (upper right). Thrombosed giant aneurysm is exposed after opening the cisterna magna (lower left) and subacute thrombus is visible in the cut surface of the specimen (lower right).