Surgical difficulties in treating aneurysms arising at the arterial wall and unrelated to fork and their histopathological characteristics were discussed. We named these aneurysms“blister aneurysms”in view of the following characteristics:(1) arising at the arterial wall unrelated to fork, mostly at the cisternal portion of the internal carotid artery,(2) hemispheric shape and small in size, i. e., 1 to 4mm in diameter, and (3) fragility. We experienced five cases of blister aneurysms. Their outcome was severe disability in one and death in four.
The causes of death were: ICA trapping due to intraoperative premature rupture in two cases and cerebral infarction due to ICA stenosis resulting from Sandt's encircling clipping and preoperative rerupture in one case each.
Arteriosclerosis around the aneurysm, in addition to defective internal elastic lamina, was the outstanding histopathological finding in the autopsy cases. Fibromuscular dysplasia was also noted in one case. The true mechanism of such blister aneurysm is unclear. Stehbens stated that small aneurysms have rather thinner walls.
For such reasons as mentioned above, our surgical attitude with regard to blister aneurysms is as follows. Neck clipping is contraindicated in most cases, even if the aneurysm has a clippable neck because the aneurysmal neck may be unable to tolerte the tension of the clip.
Safer surgical techniques for such aneurysms are summarized as follows: at first, secure the ipsilateral cervical internal carotid artery prior to accessing the aneurysm and thereafter (a) muscle encasement of the aneurysm,(b) EC-IC bypass followed by intravascular balloon occlusion of the parent artery at the aneurysmal neck or (c) EC-IC bypass after application of Sandt's encircling clip.
Treatment with Sandt's clip alone may cause arterial narrowing, and additional bypass on the ipsilateral ICA territory may be mandatory.
