Spontaneous Rupture of a Parietal Arachnoid Cyst Causing an Intracystic Hemorrhage and a Subacute Subdural Hematoma.

Arachnoid cysts are extra-axial cerebrospinal fluid collections located in the arachnoid space that usually do not communicate with the ventricular system. They are commonly found in the middle cranial fossa around the Sylvian fissure. Most of them are asymptomatic, but subdural collections or intracystic hemorrhages can complicate their natural course.