A Rare Occurrence of Arachnoid Cyst in a Patient of Mental Subnormality

An arachnoid cyst is a collection of cerebrospinal fluid (CSF) that develops in the membrane enveloping arachnoid matter in the brain or spinal cord.It is a common intracranial expansive condition, often discovered incidentally.With a prevalence of 0.5 to 2.7%, it occurs more commonly in men than women.It is mostly treated conservatively.In case of severe symptoms due to mass effect, surgical intervention may be indicated.To the best of the authors' knowledge, no aetiological significance has been ascribed to arachnoid cyst in the pathogenesis of psychiatric illnesses yet.Although there is recent evidence of arachnoid cysts occurring in patients with psychosis, it is usually labelled as an incidental finding.Here, the authors report a rare and unusual finding of an arachnoid cyst in a case of intellectual development disorder.