Clinical differences between angiographically negative, diffuse subarachnoid hemorrhage and perimesencephalic subarachnoid hemorrhage

Objective: To identify prognostic factors for vasospasm, hydrocephalus, and clinical outcomes in patients with angiographically negative, non-traumatic, diffuse subarachnoid hemorrhage (d-SAH). Methods: Retrospective review of patients who experienced angiographically negative SAH at our institution over the past 6 years was undertaken. The patients were stratified based on grade at presentation, severity, and pattern of SAH on initial non-enhanced, computed tomography (CT) of the head into perimesencephalic and diffuse subtypes. The patients were further differentiated based on the development of vasospasm, hydrocephalus and required treatments, and clinical outcomes. Patients were excluded if a causative lesion was discovered subsequently. Results: Ninety-four patients with angiographically negative SAH were identified. A total of 31 patients were considered to have the perimesencephalic (p-SAH) subtype, while 63 patients fit criteria for the diffuse (d-SAH) subtype. Compared to the p-SAH subtype, those patients with d-SAH subtype had significantly higher risk for complications related to SAH with an increased incidence of hydrocephalus (50.8% vs. 9.6%), requirement for external ventricular drainage (41% vs. 9.6%), and for the hydrocephalus requiring eventual permanent cerebrospinal fluid diversion (20.6% vs. 0%). Patients with d-SAH were also at an increased risk for symptomatic vasospasm (28.6% vs. 9.6%). Ultimately, only 76% of d-SAH patients achieved complete recovery and independent living, compared to 96.7% of p-SAH patients. Conclusion: The angiographically negative d-SAH pattern is associated with worse presentations and outcome. These patients are at increased risk for vasospasm and hydrocephalus requiring aggressive treatment and should therefore be cared for with a higher level of surveillance.