Posterior Fossa Arachnoid Cyst Presenting as Negative Symptoms of Psychosis.

Arachnoid cysts are benign congenital malformations, making up 1% among all the space occupying lesions (SOL). Sylvain fissure is the most common place (50%) but it can happen in any place. Patients might complain of a headache, ataxia, seizures, dizziness, and visual changes etc. The common psychiatric symptoms are psychosis, alexithymia, attention deficit and hyperactivity disorder, paranoid delusions, obsessive religiosity, sense of guilt or ruin, hallucinations, depression, insomnia, irritability and cognitive alterations etc. Recently, we presented a case of an arachnoid cyst in the right middle cranial fossa compressing temporal lobe presenting as the positive symptoms of psychosis. Here, we are presenting a case of posterior fossa arachnoid cyst which presented as severe negative symptoms.