Spontaneous progressive thrombosis and surgical resection of a giant aneurysm of the posterior cerebral artery in an 18-year-old.

The rare case is reported of an 18-year-old boy with giant fusiform aneurysm of the P1 and P2 segments of the posterior cerebral artery. The symptoms were two episodes of sudden headache with transient third-nerve palsy. The aneurysm developed into almost complete thrombosis over five months. The posterior cerebral artery distal to the aneurysm was also thrombosed and reirrigated by collateral channels without visual field deficit. The aneurysm was treated by resection. The development of this giant aneurysm, the progressive thrombosis and the clinical characteristics are discussed.