Fistula between a posterior communicating artery aneurysm and the cavernous sinus is very rare and few cases have been reported in the literature so far.

We report two patients including a 51-year-old man and a 43-year-old woman, who were known cases of treated fistula between a posterior communicating artery aneurysm and the cavernous sinus via neurosurgical clipping and embolization, who presented with decreased vision, eye proptosis, conjunctival chemosis and dilated episcleral vessels.

Further evaluation demonstrated that the patients had elevated intraocular pressure with a shallow anterior chamber.Fundus examination and imaging studies including optical coherence tomography and fluorescein angiography revealed choroidal effusion with retinal nerve fiber layer changes. Based on their history and imaging studies a diagnosis of secondary choroidal effusion with angle closure glaucoma and venous stasis retinopathy was made, and patients were treated with anti-glaucoma medications including eye drops of timolol, brimonidine, oral medication with acetazolamide and peripheral iridotomy in the affected eye.

In all patients with an internal carotid artery (or its branches) and cavernous sinus fistula, even in treated patients close ophthalmic follow-up visits must be done to reduce the risk of vision threatening side conditions like choroidal effusion and secondary angle closure glaucoma.