An unusual aneurysm of a basilar perforating artery presenting with a subarachnoid haemorrhage.

A 65-year-old man had a perimesencephalic subarachnoid haemorrhage with normal angiography initially. After a rebleed 5 days later, a repeat angiogram revealed a pea-like aneurysm a short distance behind and below the basilar bifurcation. It was not amenable to endovascular treatment and the feeding vessel was coagulated and divided at open surgery via a sub temporal approach. He developed a right hemiparesis and dysphasia, from which he slowly recovered. Basilar perforating artery aneurysms are extremely rare, with only 4 previous cases reported.