During the last 17 years, we have had 15 cases of aneurysmal regrowth or rebleeding after direct surgical treatment. In this paper, we have divided the cases into five groups according to the cause of rebleeding or regrowth, and have discussed some of the problems in each group. Group 1: Incomplete clipping or wrapping ; eight cases Most of the cases in this group had undergone initial operation more than ten years before, and incomplete obliteration of the aneurysms was attributable largely to

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... immaturity of technical skill. Most of the recent cases had anterior communicating or internal carotid artery aneurysms, the necks of which were unusually broad and did not easily accept a clip or a combination of clips. Based on the length of interval after operation, recurrent hemorrhage was divided into early (5 to 15 days after initial operation) and late (5 to 16 years) rebleeding. Early rebleeding appeared to occur when the"responsible" or"ruptured" bleb escaped clipping. In late rebleeding it was assumed that incompletely clipped necks took some time to develop an aneurysmal sac and eventually to rupture. Group 2: Mycotic aneurysm; 1 case Mycotic aneurysms often occur multiply in a single case and, for this reason, four-vessel study is mandatory to prevent recurrent hemorrhage. Group 3: Traumatic aneurysm; 1 case Two traumatic aneurysms occurred in a single case after operation for a large pericallosal artery aneurysm. Avulsion of small cortical branches from the pericallosal artery during the initial operation was responsible for these aneurysms, which bled soon after the initial operation. Use of an encircling clip should be considered whenever a tear of the arterial wall appears to be large enough to produce a postoperative traumatic aneurysm. Group 4: Aneurysmal development at a site other than the original; 3 cases We retrospectively and precisely reviewed initial angiograms in this group and discovered that small aneurysms had already been present in the initial angiograms. These aneurysms grew larger