Carotid-Cavernous Sinus Fistula Masquerading as Thyroid Eye Disease.

A 29-year-old man with a medical and social history notable for smoking presented with progressive orbital congestion, conjunctival injection, and extraocular muscle enlargement consistent with thyroid eye disease (TED). On ophthalmologic examination, tortuous episcleral vessels and blood in Schlemm's canal on gonioscopy clued an alternative diagnosis. Cavernous sinus enhancement on computed tomography also suggested a retro-orbital process. Digital subtraction angiography confirmed a low-flow indirect carotid-cavernous fistula (CCF). He subsequently underwent endovascular embolization treatment. Ocular symptoms resolved by seven weeks, and he remained ocular symptom free at six months. Eye redness and proptosis frequently cause patients to seek medical attention. In the absence of a mass or signs of infection, TED is high on the differential, especially with a smoking history and even with normal thyroid parameters. However, CCF may lurk; the authors describe key diagnostic features and management.