A Case Report of Giant Posterior Inferior Cerebellar Artery Aneurysm Simulating a Posterior Fossa Tumor

A 24-year-old female patient presented with a midline extra-axial posterior fossa lesion. We failed to suspect this lesion could be a giant thrombosed aneurysm of PICA(posteior inferior cerebellar artery) preoperatively, and didn't perform preoperative angiogram even after rather typical finding of thrombosed giant aneurysm on MRI. We suggest a giant thrombosed aneurysm should be included in the differantial diagnosis of any round extra-axial mass lesion in the skull base.