To report what we believe to be the first case in the English language literature of unilateral cavernous sinus thrombosis complicating contralateral sphenoid sinusitis.

A 62-year-old man presented to his general practitioner with a severe, right-sided, temporal headache. He was diagnosed with temporal arteritis and treated with systemic steroids. After five days, he developed right proptosis, ophthalmoplegia and ptosis. He was referred to the neurologists. After an urgent computed tomography head scan and computed tomography angiogram, a diagnosis of carotido-cavernous fistula was made. However, this was subsequently excluded after a negative cerebral angiogram. A review of the scans enabled diagnosis of right cavernous sinus thrombosis secondary to left sphenoiditis. The patient was referred to the otolaryngology team. After an urgent endoscopic sphenoidotomy and medical treatment, all symptoms and signs improved dramatically.

Sphenoiditis can lead to contralateral cavernous sinus thrombosis. Urgent surgical sphenoidotomy, with appropriate medical treatment, can be successful in this life-threatening complication.