The anatomy of the orbital vascular bed is complex, with tremendous individual variation. The main arterial supply to the orbit is from the ophthalmic artery, a branch of the internal carotid artery. The external carotid artery normally contributes only to a small extent. However, there are a number of orbital branches of the ophthalmic artery that anastomose with adjacent branches from the external carotid artery, creating important anastomotic communications between the internal and external carotid arterial systems. The venous drainage of the orbit occurs mainly via two ophthalmic veins (superior and inferior) that extend to the cavernous sinus, but there are also connections with the pterygoid plexus of veins, as well as some more anteriorly through the angular vein and the infraorbital vein to the facial vein. A working knowledge of the orbital vasculature and lymphatic systems is important during orbital, extraocular, or ocular surgery. Knowing the anatomy of the blood supply helps one avoid injury to the arteries and veins during operative procedures within the orbit or the eyelid. Inadvertent injury to the vasculature not only distorts the anatomy and disrupts a landmark but also prolongs the surgery and might compromise blood flow to an important orbital or ocular structure. Upon entering the cranium, the internal carotid artery passes through the petrous portion of the temporal bone in the carotid canal and enters the cavernous sinus and middle cranial fossa through the superior part of the forame lacerum . It proceeds forward in the cavernous sinus with the abducens nerve along its side. There it is surrounded by sympathetic nerve fibers (the carotid plexus ) derived from the superior cervical ganglion. It then makes an upward S-shaped turn to form the carotid siphon , passing just medial to the oculomotor, trochlear, and ophthalmic nerves (V1). After turning superiorly in the anterior cavernous sinus, the carotid artery perforates the dura at the medial aspect of the anterior clinoid process and turns posteriorly, inferior to the optic nerve.
External Carotid Artery Embolization of Dural Arteriovenous Malformations Involving the Cavernous Sinus