Intracranial arachnoid cysts presenting with first-episode mania and subsequent hyperammonemic encephalopathy: A case report

Intracranial arachnoid cysts are often an incidental discovery in the course of neuroimaging for other conditions. While often asymptomatic, cysts which enlarge can cause mass or pressure effects on adjacent structures. We report a 33-year-old male patient who presented with first episode of manic symptoms. Following treatment with sodium valproate patient developed altered sensorium and was subsequently diagnosed with middle cranial fossa arachnoid cysts and valproic acid-induced hyperammonemic encephalopathy that was successfully treated with enteric lactulose. There are several case reports of arachnoid cysts presenting in patients with psychiatric disorders and debating whether these cysts are a cause or co-occurrence. In 16 reported patients, who had arachnoid cysts with psychiatric symptoms, 9 had cysts exerting mass/pressure effects. Three patients had surgical intervention and showed significant improvement following surgery. So did 1 patient who was treated with mannitol infusion. Intracranial arachnoid cysts may also present with atypical psychiatric symptoms or complicate the treatment process by way of poor response or treatment emergent adverse effects. There is an important role for thorough neurological examination, neuroimaging, and vigilant use of psychotropics in such patients.