[Ruptured Cerebral Aneurysm Associated with Arachnoid Cyst].

Cerebral aneurysms and arachnoid cysts are relatively common cerebral malformations and the use of recent modalities has increased their detection rates. However, cerebral aneurysms associated with arachnoid cysts are unusual. We describe two cases of ruptured cerebral aneurysms associated with arachnoid cysts. According to previous reports, clinical presentation may sometimes be unusual, as cysts can prevent subarachnoid hemorrhage. Moreover, in some cases, CT may reveal typical arachnoid cysts without subarachnoid hemorrhage, without intracystic hematoma, or with subdural hematoma alone. These clinical presentations and radiologic findings can lead to delayed diagnosis of subarachnoid hemorrhage. Therefore, we should consider the coexistence of arachnoid cyst in case of a warning sign of aneurysm rupture.