Incidental optic nerve sheath arachnoid cyst: A rare case finding with literature review

Arachnoid cysts are the most common benign cystic abnormalities formed due to congenital splitting of the arachnoid layer. They comprise 1% of intracranial masses, and the orbital location is even more rarely reported in history especially in the pediatric population. They might be discovered as an asymptomatic finding on imaging performed for a concomitant condition or, in most reported cases, as a result of ophthalmic impairment. They can be isolated or associated with gliomas, neurofibromas, empty sella syndrome, and frontotemporal porencephalic cysts. Computed tomography scan shows a non-enhancing liquid cystic lesion, and magnetic resonance imaging remains the best assessment tool confirming the similarity of the fluid to cerebrospinal fluid and evaluating the optic nerves. Herein, we report the case of an incidental discovery of an intraorbital arachnoid cyst on magnetic resonance imaging in a 53-year-old woman with a history of epilepsy. No treatment was performed as the cystic formation was asymptomatic.