Aneurysms at nonbranching sites in the surpaclinoid portion of the internal carotid artery: internal carotid artery trunk aneurysms.

OBJECTIVE: Aneurysms at nonbranching sites in the supraclinoid internal carotid artery (ICA), known as blood blister-like aneurysms or ICA anterior or dorsal wall aneurysms, are not well understood. To clarify this clinical entity, 7408 patients with subarachnoid hemorrhage who were treated during a 5-year period were analyzed.
METHODS: Forty-eight patients had aneurysms that were intraoperatively confirmed to be located at a nonbranching site in the supraclinoid portion of the ICA. Neuroradiological and clinicopathological features and outcomes were studied.
RESULTS: The aneurysms were divided into the "blister type," with a blood blister-like configuration and fragile walls, and the "saccular type," with a saccular configuration and a relatively firm neck, like ordinary berry aneurysms. The most frequent origin was the anteromedial wall for both types. ICA dissection was associated only with the blister type, and hypertension was more frequent with the blister type (P = 0.0978). The preoperative conditions of the patients were the same, but the outcomes for patients with blister-type aneurysms were worse, because of frequent intra- and postoperative aneurysmal bleeding. Saccular-type aneurysms were safely clipped. Treatment of blister-type aneurysms by clipping on wrapping material achieved good results, but ICA trapping (P = 0.0952), clipping (P = 0.0146), and wrapping (P = 0.0110) were associated with much worse results.
CONCLUSION: Blister-type and saccular-type aneurysms have different shapes and wall characteristics. The saccular type can be treated by clipping, whereas the blister type requires clipping on wrapping material. ICA trunk aneurysms may be a better designation to express the diversity of these aneurysms, rather than ICA blood blister-like or anterior or dorsal wall aneurysms.