Marginal Sinus Arteriovenous Fistulas Mimicking Carotid Cavernous Fistulas: Diagnostic and Therapeutic Considerations

SUMMARY: Marginal sinus fistulas (MSFs) are uncommon vascular anomalies. Occasionally, the dominant venous drainage is forced retrograde up the inferior petrosal sinus and into the cavernous sinus, causing chemosis, proptosis, and ocular hypertension, mimicking a carotid cavernous fistula. This atypical clinical presentation may lead to misdiagnosis and inappropriate hazardous treatment of an MSF. Identifying the site of the fistula and understanding the anatomy of the venous drainage are critical in providing appropriate, safe, and efficacious endovascular treatment. The marginal sinus surrounds the foramen magnum, com-municating anteriorly with the venous plexus of the clivus and posteriorly with the occipital sinus (if present). Corre-spondingly, dural fistulas of the marginal sinus typically drain via the sigmoid sinus–jugular bulb.1 However, in some cases, the jugular venous outflow becomes stenotic or thrombosed, forcing the venous drainage retrograde through the inferior petrosal sinus (IPS) and into the cavernous sinus (CS). Pa-tients with this anatomy may present with clinical findings identical to those of a carotid cavernous fistula (CCF).2 The clinical or angiographic misdiagnosis of a marginal sinus fistula (MSF) may lead to inappropriate or dangerous treatment. We review the clinical presentation, imaging find-ings, and endovascular treatment of 2 patients with MSFs, which presented clinically as CCFs