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. Cases of intracystic hemorrhage and subdural hematoma, especially in the absence of traumatic events, have been scarcely reported. Arachnoid cysts outside the middle cranial fossa are rarely associated with an intracystic hemorrhage. We present the case of a 10-year-old boy with a known right parietal brain arachnoid cyst who complained of progressive headaches for three days. There was no history of trauma. The head CT scan showed a 2-cm isodense subacute subdural hematoma, causing a mass effect on the underlying brain. It was associated with a right parietal arachnoid cyst containing intracystic subacute blood. The symptoms were relieved after burr-hole surgical drainage of the intracystic hemorrhage and associated subacute subdural hematoma.