Abstract
A 14-year-old boy who had been complaining of double vision for the previous month was referred for neuro-ophthalmological evaluation. He was carrying a diagnosis of a cavernous sinus haemangioma causing a right VIth nerve palsy, based on imaging elsewhere. He reported having a boil at the angle of his mouth, which was associated with left-sided facial cellulitis, two weeks before the onset of the diplopia. His blood investigations showed a leukocytosis with elevated inflammatory markers. Re-evaluation of the magnetic resonance imaging suggested a sac-like out-pouching in the intracavernous part of the right internal carotid artery with differential intensity suggestive of turbulent flow. On the basis of the clinico-radiological findings, a diagnosis of mycotic aneurysm of the cavernous sinus part of internal carotid artery was made. A high index of suspicion is required to detect this rare clinical entity, which is associated with a potentially catastrophic clinical course.