Aggressive CSF Diversion Reverses Delayed Cerebral Ischemia in Aneurysmal Subarachnoid Hemorrhage: A Case Report

External ventricular drain (EVD) placement temporarily provides cerebrospinal fluid (CSF) diversion and is indicated in patients with aneurysmal subarachnoid hemorrhage (aSAH) to relieve hydrocephalus. Case report. A 56-year-old woman was admitted to our hospital with aSAH complicated by acute hydrocephalus. An EVD was placed and set to 15 mmHg. After nearly 72 h, she clinically deteriorated. A computed tomography (CT) perfusion scan showed hypoperfusion in the watershed regions in both hemispheres and CT angiogram showed mild segmental arterial narrowings. After the EVD was lowered to 5 mmHg, the radiologic perfusion abnormalities and clinical symptoms resolved. We postulate a mechanism by which CSF diversion could decrease the risk of delayed cerebral ischemia after aSAH: CSF drainage at low levels of intracranial pressure (e.g., 5 mmHg) could improve blood flow in the microcirculation, and thus improve tissue perfusion.