Hemorrhagic Arachnoid Cyst of the Posterior : A Case Report

Abstract

Arachnoid cysts are reported to be occasionally associated with subdural hematoma or hygroma. Spontaneous disappearances of arachnoid cysts have been reported previously and in was emphasized that rupture of cyst membrane and subdural hematoma or hygroma must be essential for them to disappear. We report herein a case of hemorrhagic arachnoid cyst of the posterior fossa. The hemorrhagic cyst was not accompanied by subdural hematoma or hygroma and gradually reduced in size. A 21-year-old man sustained a cerebral contusion and epidural hematoma of the frontal reglon from a head injury. Computerized tomography scannlng obtained 12 hours after the inJury revealed a hemorrhagic retrocerebellar arachnoid cyst. Magnetic resonance imaging performed on day 21 revealed that the hemorrhagic arachnoid cyst had high intensity on a T1-weighted image and relatively low intensity on a T2- weighted image without subdural hematoma or hygroma. Follow-up CT scans revealed that the hemorrhagic arachnoid cyst had reduced in size. The patient made an almost complete recovery and was discharged with no observable neurologlcal deficits three months after admission. Hemorrhage was not presentin the first few hours after head injury but developed Subsequently, confined strictly to the cystic cavity. This case report provides evidence that disappearance or reduction of arachnoid cysts can occur without the need for subdural hematoma or effusion.