Intraoperative aneurysmal subarachnoid hemorrhage after rupture of a previously undiagnosed intracranial aneurysm during Chiari decompression: case report and literature review

Type 1 Chiari malformation occurs when caudal displacement of cerebellar tonsils below the level of foramen magnum obstructs the normal flow of cerebrospinal fluid (CSF) between the cranial and spinal spaces, a condition that often needs surgical decompression to restore normal CSF circulation. Abrupt changes in CSF flow dynamics after Chiari decompression can affect the intracranial CSF dynamics to the extent that a previously undiagnosed intracranial aneurysm remote from the site can rupture. The authors describe the development of intraoperative aneurysmal subarachnoid hemorrhage that occurred as a result of spontaneous rupture of a previously undiagnosed right distal posterior inferior cerebellar artery in a 57-year-old woman with type 1 Chiari malformation who was undergoing surgical decompression. The mechanism of the aneurysmal rupture appears to be related to the changes of CSF flow dynamics during surgical decompression. Normally, pressure equilibrium between the two sides of the aneurysmal wall prevents its rupture, but factors that significantly affect this equilibrium, such as systemic hypertension, can cause the aneurysm to rupture. The concept of spontaneous intraoperative rupture of intracranial aneurysm remote from the site of surgery has been described twice previously but under different scenarios. This scenario, to the best of our knowledge, has not been previously described.