Carotid-Cavernous Fistula

Overview

An abnormal communication between the carotid circulation and the cavernous sinus, arterialising the orbital venous drainage. Two patterns matter clinically: the DIRECT (high-flow) fistula, typically after head trauma in a younger patient — abrupt pulsatile proptosis, chemosis, a bruit the patient may hear — and the INDIRECT (dural, low-flow) fistula, typically spontaneous in an older, often hypertensive patient, presenting as a chronically red, quietly congested eye that is repeatedly treated as conjunctivitis or cellulitis. The recognisable signature is arterialised, corkscrew episcleral vessels running to the limbus, raised IOP on the affected side, and orbital congestion WITHOUT fever or tenderness. Diagnosis is by imaging; definitive management is endovascular.