Right Indirect Carotid-Cavernous Fistula Presenting With Isolated Oculomotor Palsy: A Diagnostic Challenge and Successful Endovascular Management.

Carotid-cavernous fistulas are abnormal communications between the carotid arterial system and the cavernous sinus. Indirect carotid-cavernous fistulas are low-flow lesions that may sometimes present subtly and mimic inflammatory or neoplastic cavernous sinus disease. We report the case of a 76-year-old man with diabetes and hypertension who developed painless diplopia and right-sided partial ptosis over two weeks. Clinical examination revealed right incomplete third nerve palsy with pupillary involvement. Magnetic resonance imaging showed enhancing soft tissue thickening in the right cavernous sinus, raising suspicion of an inflammatory process. He was treated with corticosteroids after appropriate glycemic control but showed no improvement. Further evaluation with positron emission tomography and cerebrospinal fluid analysis excluded malignancy and infection, although serum galactomannan and IgG4 were mildly elevated, complicating the diagnostic picture. The lack of response to steroids and inconclusive imaging prompted consideration of a vascular etiology. Digital subtraction angiography ultimately confirmed an indirect carotid-cavernous fistula draining via the inferior petrosal sinus. The patient underwent transvenous coil embolization under general anesthesia, achieving near-complete occlusion of the fistula. The procedure was uneventful, and the patient experienced complete resolution of diplopia and ptosis at one-month follow-up. He was discharged in stable condition with multidisciplinary follow-up. This case highlights how indirect carotid-cavernous fistulas can mimic other cavernous sinus pathologies, how misleading ancillary tests may complicate diagnosis, and the critical importance of angiographic evaluation when non-invasive imaging is inconclusive. Endovascular transvenous coil embolization provided safe and effective treatment with favorable clinical outcomes.