Carotid ring 近傍の脳動脈瘤の分類と治療

Abstract

Carotid artery aneurysms arising near the dural ring and the ophthalmic segment pose conceptual and technical controversies with regard to their classification and the extent of anterior skull base exposure. We review 58 operated patients with 60 such aneurysms and propose surgical procedure-orientated classification. According to the direction and size of the aneurysms, we classified them into 4 categories: supraoptic type, suboptic type, paraophthalmic type and global type. The supraoptic type include true ophthalmic artery aneurysms and “blister aneurysms” at the anterior wall of the carotid artery. The suboptic type arising at the superior hypophyseal artery necessitates the optic canal opening for obliteration with fenestrated clips. The paraophthalmic type had no branches near the aneurysm and opening the optic canal and removal of the anterior clinoid process is usually not necessary. The global type is often found by visual symptoms, and extensive exposure near the distal ring is necessary. Aneurysms arising near the dural ring have been frequently reported and the normenclature and the indication of the treatment have seemed to be confused. The risk of causing subarachnoid hemorrhage is the most important concern and the anatomical relation of the aneurysm and the distal ring is critical. When the C2 and C3 border is defined as the distal ring, the terminology of the nearby aneurysms becomes simple. However, accurate preoperative assessment of the border from the imaging study is not always possible. That is why the distal ring runs obliquely along the longitudinal axis of the C2 and C3, and the branching point of the ophthalmic artery does not always correspond to the C2 and C3 border. We discuss surgical indication and our understanding of reported aneurysms near the distal ring such as infraclinoidal aneurysm, transitional cavernous aneurysm and carotid cave aneurysm.