Preoperative angiographical prediction of the necessity to removal of the anterior clinoid process in internal carotid-posterior communicating artery aneurysm surgery.

During the last 10 years, we had to resect the anterior clinoid process (ACP) before applying the clip in three of the 70 patients with internal carotid-posterior communicating artery (ICPCom) aneurysms. To reveal the angiographic characteristics in these three patients, we measured the following parameters on carotid angiograms in all 70 patients: 1) the angle between the midline of the skull and the axis of the C1 segment of the internal carotid artery (ICA) on A-P view (angle A). 2) the angle between the axes of the C1 and C2 segments of the ICA on A-P view (angle B). and 3) the distance between the posterior wall of the carotid "knee" and the proximal aneurysmal neck on lateral view (distance d). The common angiographic features of these three patients were as follows: 1) angle A was larger than 60 degrees. 2) angle B was less than 90 degrees. 3) distance d was less than 10 mm. and 4) the posterior communicating artery was of the foetal type. The present results suggest that preoperative angiogram can predict whether or not the ACP should be removed during ICPCom aneurysm surgery.