We report five cases of giant aneurysm in the posterior fossa; arising from the posterior inferior cerebellar artery in 1, the vertebral artery in 2 and the vertebrobasilar artery in 1 patient. The origin of aneurysm was unknown in 1 patient in whom a completely thrombosed aneurysm was located in the cerebellopontine angle. Two patients underwent surgical treatment. One patient who underwent resection of a giant and multiple aneurysms of the distal posterior inferior cerebellar artery had a good result. The other patient who underwent partial aneurysmectomy of a giant thrombosed aneurysm of the vertebral artery had postoperative hemorrhage and died 10 months after the operation. Two patients, 1 with a partially thrombosed giant aneurysm of vertebral artery and the other a giant fusiform vertebrobasilar artery were managed conservatively and died due to progressive brainstem compression and ischemia. Managements of giant aneurysms in the posterior fossa were discussed.
