Huge arachnoidal cyst with recent onset of seizure in an adult

A 68-year-old right-handed man, having consulted for the occurrence of a first epileptic seizure. Brain computerized tomography (CT) scan and magnetic resonance imaging (MRI) showed a giant congenital supratentorial arachnoidal cyst occupying the anterior two thirds of the right hemisphere, measuring 14.09x6.07 (APxT) cm and 11.67cm high, compressing the right cerebral hemisphere and the right cerebral peduncle with a midline shift. Arachnoidal cysts are congenital malformations containing cerebrospinal fluid. They may be asymptomatic and discovered incidentally on imaging. When they are large, as in this patient, they can cause a mass effect.