Delayed cavernous sinus dural arteriovenous fistula with aggressive venous reflux after transsphenoidal surgery for pituitary adenoma

Background Carotid-cavernous fistula (CCF) after transsphenoidal surgery is rare and usually represents a direct fistula related to internal carotid artery injury. Delayed cavernous sinus dural arteriovenous fistula (CS-dAVF)/indirect CCF without recognized carotid injury has only exceptionally been documented. Case description A man in his 70s underwent endoscopic transsphenoidal surgery for a non-functioning pituitary adenoma without recognized internal carotid artery injury or arterial bleeding. Immediate postoperative MRI showed no apparent vascular abnormality. Two months later, while asymptomatic, time-of-flight magnetic resonance angiography showed subtle high signal in the right cavernous sinus. Six months postoperatively, he developed diplopia due to right abducens nerve palsy, followed by eyelid swelling and conjunctival congestion. Repeat imaging demonstrated superior ophthalmic vein dilation, and angiography revealed a Barrow type D CS-dAVF/indirect CCF with aggressive posterior intracranial venous reflux. Compartment-oriented transvenous embolization through the inferior petrosal sinus abolished both orbital venous drainage and posterior intracranial reflux. Symptoms improved, and no recurrence occurred over 10 years. Conclusion Delayed CS-dAVF/indirect CCF can occur after transsphenoidal surgery even without recognized carotid injury. Subtle postoperative cavernous sinus signal on time-of-flight magnetic resonance angiography may provide an early diagnostic clue before overt orbital venous signs develop.