Surgical treatment of internal carotid siphon aneurysms

Abstract

Surgical treatment of internal carotid (IC) artery aneurysms around the carotid siphon is discussed. We resent 54 cases including 16 of giant aneurysms. The surgical approaches to the aneurysms in this region are as follows: 1) A frontotemporal approach with the patient in a 45 semi-sitting position to decrease venous pressure, 2) A Dolenc approach with incision of part of the dura mater of the superior orbital fissure to facilitate removal of the anterior clinoid process and unroofing of the optic canal, and 3) Opening of the medical triangle followed by transection of the optic canal and dural sheath. Carotid siphon aneurysms can be divided into three groups anatomically : aneurysms of the ophthalmic segment (C2), of the clinoid segment (C3), and of the horizontal segment (C4). We present 29 cases of aneurysms arising from the C2 or C2/3 segment, 14 cases arising from the C3 or C3/4 segment, and 11 cases arising from the C4 segment. The anatomic locations of the aneurysms were determined preoperatively using angiography and three - dimensional CT imaging. Small aneurysms of the ophthalmic segment projecting inferomedially can be clipped using a contralateral approach via the prechiasmatic route. Aneurysms of the ophthalmic segment projecting superiorly can be clipped following resection of the anterior clinoid process. The clinoid process should be resected intradurally with direct visualization of the aneurysms. Straight side angled clips are suitable for these aneurysms. Carotid cave aneurysms, which include aneurysms of the ophthalmic segment oriented inferomedially and of the clinoid segment projecting posteromedially, can be clipped using curved fenestrated clips via Dolenc's extradural approach. For accurate clipping, opening of the medial triangle and full mobilization of the IC at the clinoid segment and optic nerve by unroofing of the optic canal required. Aneurysms of the horizontal portion ar clipped after full exposure of the artery in the cavernous sinus only when the aneurysms are large and symptomatic. We used the frontotemporal and Dolenc approaches and applied fenestrated clips to aneurysms oriented posteromedially and straight or oblique clips to aneurysms projecting anterolaterally. Forty aneurysms were clipped using these approaches with 36 cases (90%) resulting in favorable postoperative recovery. There were 3 deaths secondary to complication of vasospasm and 3 cases with postoperative visual loss. The classification of these aneurysms and the surgical techniques we employed are discussed in detail.