Intracystic Hemorrhage in a Posterior Fossa Arachnoid Cyst following Severe Head Injury : A Case Report

A case of intracystic hematoma in a posterior fossa arachnoid cyst in a young man following a severe head injury was reported. An otherwise healthy 34-year-old man was admitted in a comatose state following a head injury suffered in a traffic accident while riding a motorcycle. A computed tomography scan on admission showed a small hemorrhage in the left anterior thalamus, subarachnoid hemorrhage in the interpeduncular cistern, moderate brain swelling, and a high density area in a cystic cavity posterior to the cisterna magna. The patient's head injury was treated conservatively under continuous monitoring of the intracranial pressure. Magnetic resonance images taken two weeks after the onset revealed several T2 high intensity signals in the deep white matter and the corpus callosum as well, suggesting a diffuse axonal injury. The posterior fossa cyst having intracavitary hemorrhage was diagnosed as an arachnoid cyst associated with intracystic hemorrhage. He regained his consciousness gradually and showed loss of motor function in the right extremities. Fortunately he could walk without any aid after a rehabilitation program. Arachnoid cysts may associate with various types of intracranial hematoma such as subdural, intracystic, and rarely, epidural hematomas following head injuries, even mild. Although arachnoid cysts in the posterior fossa are occasionally encountered incidentally, all hemorrhagic complications but one reportedly occurred in the supratentorial cranial cavity. Considering the mechanisms of traumatic brain injury, more severe traumatic force may be necessary to cause hemorrhagic complications in arachnoid cysts of the posterior fossa.