[Cranial injury disclosing an asymptomatic arachnoid cyst of the sylvian fossa].

In a 21 year-old man suffering from a post-traumatic neurotic syndrome, the cranial CT scan revealed an arachnoid cyst in the left Sylvian fissure, which had been completely asymptomatic before. The surgical emptying of the cyst modified neither the CT finding nor the neurotic syndrome. The latter disappeared once the insurance controversy was resolved. After a review of the etio-pathogenesis of arachnoid cysts, our patient's malformation was identified as the so-called "Temporal Lobe Agenesis Syndrome". On that basis, any medico-legal correlation between the head injury and the cystic malformation was excluded.