Collateral pathways between the cavernous portion of the internal carotid and external carotid arteries.

Abstract

Extensive arterial anastomoses exist between the cavernous portion of the internal carotid artery and the external carotid artery. These arterial channels are seldom visible in the normal patient. They may enlarge, however, and become roentgenographically visible when they act as collateral pathways between the internal and external carotid arteries. In this report, we will review the anatomy of the arterial anastomosis between meningeal branches of the external carotid artery and the artery to the inferior cavernous sinus, a branch of the internal carotid artery. The clinical and roentgenographic findings in six patients in whom this pathway was visualized will be described. Anatomy The anatomy of the cavernous branches of the internal carotid artery has been reviewed extensively (3–7). The three main branches of the cavernous carotid artery are the meningohypophyseal trunk, the artery to the inferior cavernous sinus, and the capsular arteries of McConnell. The meningohypophyseal trunk, the first branch of the cavernous carotid artery, trifurcates into three branches of nearly equal caliber. These divisions are: (a) a tentorial artery, (b) a dorsal meningeal artery, and (c) an inferior hypophyseal artery. Parkinson (3, 4) noted that the meningohypophyseal trunk was present in all 200 necropsy specimens studied. In 80 per cent of the specimens, another main trunk arose from the internal carotid artery 0.5 cm anterior to the origin of the meningohypophyseal trunk (3). This branch, the artery to the inferior cavernous sinus, supplies the structures within the inferior cavernous sinus and its dural covering. It courses over the sixth nerve and gives branches to the gasserian ganglion. Branches of this trunk anastomose directly with the middle meningeal and accessory meningeal arteries near the foramen spinosum. When the artery to the inferior cavernous sinus is absent, the blood supply is assumed by branches of the meningohypophyseal trunk (2). The collateral pathway between the artery to the inferior cavernous sinus and the meningeal branches of the internal maxillary artery has been discussed previously in the anatomic literature (3–7). The following case reports illustrate this anastomotic channel as demonstrated by neuroradiologic studies. Case Reports Case I: This 62-year-old man had complete occlusion of the right internal carotid artery due to arteriosclerosis. The external carotid artery and its branches were well opacified. The cavernous portion of the internal carotid artery was filled via anastomoses between the internal maxillary artery and the artery to the inferior cavernous sinus (Fig. 1). Case II: A 52-year-old woman had a cerebrovascular accident with residual left facial weakness. Carotid arteriography revealed a complete occlusion of the right internal carotid artery. The carotid siphon was filled via the ophthalmic artery and the artery to the inferior cavernous sinus.