Vascular Drainage of the Orbit and Cavernous Sinus Each cavernous sinus contains a plexus of veins draining the orbits and some of the intracranial veins (▶ Fig. 15.1). The carotid artery passes through the cavernous sinus. Vascular disorders are a common cause of cavernous sinus and orbital syndromes. Fig. 15.1 Lateral view of the orbit showing the venous drainage of the orbit. (From Schuenke M, Schulte E, Schumacher U, Ross LM, Lamperti ED, Voll M. THIEME Atlas of Anatomy, Head and Neuroanatomy. Stuttgart, Germany: Thieme; 2007. Illustration by Karl Wesker.) The major orbital veins include the superior and the inferior ophthalmic veins. The cavernous sinus is connected anteriorly to the superior and inferior ophthalmic veins and posteriorly to the superior and inferior petrosal sinuses (▶ Fig. 15.2). There are numerous communications between the facial veins and the orbital veins, explaining why facial infections are often complicated by orbital cellulitis and rarely by cavernous sinus thrombosis. Impaired venous drainage results in orbital congestion, which presents like an orbital syndrome. Fig. 15.2 Clinically important vascular relationships in the facial region. (From Schuenke M, Schulte E, Schumacher U, Ross LM, Lamperti ED, Voll M. THIEME Atlas of Anatomy, Head and Neuroanatomy. Stuttgart, Germany: Thieme; 2007. Illustration by Karl Wesker.) Aneurysms of the internal carotid artery may develop within the cavernous sinus (▶ Fig. 15.3 and ▶ Fig. 15.4). They are often asymptomatic until patients develop diplopia (ocular motor nerve compression) and ipsilateral pain (trigeminal nerve compression). Fig. 15.3 a, b (a) Complete left ptosis and ophthalmoplegia with headache from a left cavernous sinus aneurysm. (b) Coronal T1-weighted magnetic resonance imaging of the brain with contrast showing a round mass in the left cavernous sinus consistent with an aneurysm (arrow) of the left internal carotid artery in the cavernous sinus. Fig. 15.4 a, b (a) Source image of a computed tomographic angiogram (CTA) with contrast showing a left cavernous sinus aneurysm (arrow). (b) Angiographic reconstruction of the CTA showing a large aneurysm (outlined) of the left internal carotid artery within the cavernous sinus. An ipsilateral third-order Horner syndrome may be present. There is usually no visual loss. A carotid-cavernous fistula (CCF) is an abnormal communication between the carotid artery and the cavernous sinus, a venous plexus (▶ Fig. 15.5). The cavernous sinus fills with arterial blood, and the pressure increases. This results in impaired drainage of all veins normally draining into the cavernous sinus with resultant venous congestion (▶ Fig. 15.6). Fig. 15.5 Sagittal view of the cavernous sinus and posterior part of the orbit showing a carotid cavernous fistula. Fig. 15.6 Catheter angiogram (lateral view) showing a direct carotid cavernous fistula (black arrow). Note the dilated superior and inferior ophthalmic veins (red arrows). CCFs can be classified by four different schemes: Etiologically (traumatic or spontaneous) Hemodynamically (high flow or low flow) Anatomically (direct or dural) Angiographically: Type A fistulas are direct shunts between the internal carotid artery and the cavernous sinus. They represent from 70 to 90% of all CCFs, are usually of the high-flow type, and most often are posttraumatic. They can also arise from rupture of an intracavernous carotid artery aneurysm or from complications of surgery or catheter angiography. Because of the high blood flow rate, direct CCFs usually manifest with acute and severe symptoms, and they rarely resolve spontaneously. Types B, C, and D are indirect or dural shunts. They represent congenital arteriovenous connections between small arterial branches and the cavernous sinus that open spontaneously in older women or in the setting of hypertension, diabetes, atherosclerotic disease, childbirth, or collagen-vascular disease. Dural CCFs usually cause insidious and less severe symptoms. In contrast to direct fistulas, dural shunts are much more likely to be misdiagnosed initially and to resolve spontaneously. As a result of these abnormal communications between arteries and veins, and because of the baseline pressure gradient between the two, the affected veins become “arterialized,” with a resultant elevation in intravenous pressure and changes in the hemodynamics of the involved vasculature, including rate and direction of blood flow (▶ Fig. 15.7, ▶ Fig. 15.8, ▶ Fig. 15.9). Fig. 15.7 Indirect right carotid-cavernous fistula with arterialization of the conjunctival vessels in the right eye, mistaken for months as chronic conjunctivitis.
15.2 Carotid-Cavernous Aneurysms
15.3 Carotid-Cavernous Fistulas
15.3.1 Classification
15.3.2 Features
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