Arachnoid cysts associated with post-traumatic and spontaneous rupture into the subdural space.

Post-traumatic or spontaneous rupture of an arachnoid cyst resulting in a subdural haematoma is rare. Much more rarely, a ruptured arachnoid cyst may be present with a subdural CSF collection without evidence of haemorrhage. These are most commonly seen in the middle cranial fossa, where arachnoid cysts occur most frequently. In this paper, five teenage patients (four male, one female) are reported with post-traumatic or spontaneous arachnoid cyst ruptures, resulting in subdural haematomas in four patients and a subdural CSF collection without haemorrhage in one patient. Possible pathogenesis of the condition is discussed.