Preoperative predictive value of the necessity for anterior clinoidectomy in posterior communicating artery aneurysm clipping

Objective: Resection of the anterior clinoid process (ACP) for the clipping of an internal carotid-posterior communicating artery aneurysm is rarely needed. However, preoperative awareness of the necessity of anterior clinoidectomy is essential for safe clipping of the lesions. We investigated the preoperative predictive value for anterior clinoidectomy in treating internal carotid-posterior communicating artery aneurysms. Methods: We retrospectively reviewed all patients with a posterior communicating artery aneurysm treated with clipping in the past 5 years. Only the patients who underwent both computed tomographic angiography and 4-vessel digital subtraction angiography were included in this study. We measured several angles and distances on these images, and compared the parameters measured between an anterior clinoidectomy group and a non-anterior clinoidectomy group. A P value of less than 0.05 was considered significant. Results: We examined 94 cases of posterior communicating artery aneurysms treated with clipping. The ACP was resected in 6 of the 94 cases. In the anterior clinoidectomy group, there were 3 factors that were statistically significant. First, the calculated real distance between the ACP and the aneurysmal neck was shorter (mean, 4.4 ± 0.7 versus 7.2 ± 1.4 mm). Second, the angle between vertical line to cranial base and communicating segment of the internal carotid artery (ICA) was larger (mean, 62.5 ± 4.6 versus 50.9 ± 10.7 degrees). Third, the angle between the communicating segment and the ophthalmic segment of the ICA was smaller (mean, 66.5 ± 15.1 versus 84.6 ± 20.4 degrees). Conclusion: The anterior clinoidectomy group showed a more tortuous course of intracranial ICA around the ACP than the nonclinoidectomy group. Therefore, measurement of the distal ICA angle is helpful in predicting the necessity of anterior clinoidectomy.