Treatment of unruptured cerebral aneurysms--a multi-center study of Japanese national hospitals.

The treatment and natural course of unruptured cerebral aneurysms were analyzed in 427 cases of unruptured cerebral aneurysm registered at five Japanese national hospitals. Of these cerebral aneurysms 295 were treated by craniotomy, and 22 with endovascular coil embolization. Neurological deterioration after treatment occurred in 31 (9.8%) of the 295 craniotomies and 3 (13.6%) of the 22 endovascular treatments. There was no subarachnoid hemorrhage (SAH) reported after the craniotomies whereas one case of SAH was reported after endovascular treatment. For 145 aneurysms in 110 cases, the natural course of the aneurysms was observed without surgical treatment. During the follow up period of in total 2,610 months (217.5 years), seven of these aneurysms ruptured, resulting in a rupture rate of 3.2%/year. Three of these seven aneurysms were less than 10 mm in diameter. The likelihood of an unruptured cerebral aneurysm to rupture was not exceedingly low. Since the risk of rupture and the morbidity related to surgical treatment cannot be predicted by size alone, the morphology, location and condition of the patients should be considered when treating unruptured cerebral aneurysms.