To report a rare case of a spontaneous carotid cavernous fistula (Barrow type D), presenting as refractory, prolonged unilateral conjunctival injection, soreness, and increased intra-ocular pressure.

Carotid cavernous fistula (CCF) is an abnormal arteriovenous communication between the carotid arterial system and the venous cavernous sinus. They are classified as direct (high-flow, involving a direct connection between the internal carotid artery and the cavernous sinus) or indirect/dural (low-flow, involving meningeal branches of the internal or external carotid arteries and the cavernous sinus). They can present with various ocular complaints, often mimicking common conditions like conjunctivitis. Delayed diagnosis or treatment can lead to serious complications including vision loss.

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A 73-year-old female with a history of hypertension, hyperlipidemia, obstructive sleep apnea, and migraine presented with six weeks of left eye redness and soreness that was initially diagnosed as conjunctivitis. Symptoms persisted despite treatment with topical antibiotics. Examination revealed conjunctival corkscrew vessels, mild proptosis, anisocoria, and elevated intraocular pressure (27 mmHg). CT angiography demonstrated abnormal vessels arising from the left cavernous internal carotid artery with enlargement of the ophthalmic artery, suspicious for a carotid cavernous fistula. Diagnostic cerebral angiography confirmed a Barrow type D CCF with shunting from branches of both internal and external carotid arteries into the left cavernous sinus. Patient underwent successful transvenous embolization through a venous channel from the left internal jugular vein, with complete resolution of symptoms postoperatively and normalization of intraocular pressure.

This case highlights the importance of consideration of CCF in patients with persistent unilateral conjunctivitis despite standard medical therapy. Recognition of atypical findings such as elevated intra-ocular pressure and proptosis should prompt vascular imaging. It also demonstrates that alternative venous pathways, such as direct channels from the internal jugular vein, can provide access to the cavernous sinus when typical routes (Inferior petrosal sinus) are unavailable.