Optic Strut as a Radiographic Landmark in Evaluating Neck Location of a Paraclinoid Aneurysm

Abstract

The optic strut (OS) is a candidate landmark in computed tomographic (CT) angiographic scans for the discrimination of intradural and extradural/intracavernous aneurysms involving the paraclinoid segment of the internal carotid artery. The goal of this study is to examine and confirm the qualifications of the OS as a landmark in CT angiographic scans for the preoperative evaluation of aneurysms in this region. Seventeen consecutive patients with 18 unruptured paraclinoid aneurysms who underwent preoperative CT angiography scans and direct surgery between 1998 and 2005 were evaluated retrospectively. We focused on the relationships of the necks of aneurysms to the OS in CT angiographic scans and that of the necks to proximal dural rings during intraoperative examinations. Direct surgery revealed that 14 aneurysms, the necks of which were distal to the OS on CT angiographic scans, arose distal to the proximal dural rings. All aneurysms were clipped, except one exhibiting calcification of the neck. Three aneurysms, for which the neck was proximal to the OS on CT angiographic scans, revealed only a portion or nothing of their domes instead of their necks through the proximal dural rings after dissection of the distal dural rings. Dome coating with fibrin glue and a piece of muscle tissue or mere exploration was performed. Another aneurysm, of which the neck straddled the OS on CT angiographic scans, was found to arise across the proximal dural ring. Clipping of the neck was performed after dissection of the proximal dural ring. Of the source images of CT angiographic scans, the axial images were the most useful in evaluating the relationship of the neck of an aneurysm to the OS. On CT angiographic scans, the OS is a precise identification of the proximal dural ring that forms the superior border of the cavernous sinus. The aneurysms whose necks arise obviously distal to the OS on CT angiographic scans are able to be clipped without dissection of the proximal dural ring.