A giant basilar artery perforator aneurysm.

Basilar artery perforator aneurysms (BAPA's) are a rare entity. Their natural history and treatment are unclear. We describe the largest BAPA reported thus far in literature in a 64-year-old Caucasian woman. This patient did not present with subarachnoid hemorrhage, but with left hemiparesis due to pontine ischemia. The aneurysm was initially misdiagnosed as a tumoral mass in a referring center. Angiography confirmed the presence of a BAPA and a flow diverter was successfully placed. This case shows us that a BAPA can mimic a tumoral mass and can cause ischemia due to mass effect without having ruptured. Both conservative and flow diverter placement seems viable treatment options. Individual patient characteristics and preferences should be considered in decision-making for treatment.