Aneurysmal Versus “Benign” Perimesencephalic Subarachnoid Hemorrhage

Abstract

Background The rate of underlying ruptured aneurysms, complications, and their relevance to outcomes in “benign” perimesencephalic subarachnoid hemorrhage are not well known and underreported. Methods Retrospective analysis of patients with perimesencephalic subarachnoid hemorrhage from a large tertiary care center (2007–2022). Results Eighty‐one patients were included with mean age of 55.5 ± 10.3 years. An underlying ruptured aneurysm was diagnosed in 5 patients (6.2%); 3 (60%) had negative computed tomography angiography and they were detected only in digital subtraction angiography (2 on initial digital subtraction angiography and 1 on follow‐up digital subtraction angiography). The most common complication was vasospasm in 25/81 patients (31%), and the majority 21/25 (84%) were asymptomatic. Symptomatic vasospasm occurred at a significantly higher rate among patients with underlying aneurysm (40% versus 2.6%; P  = 0.01). Hydrocephalus occurred in 10% of patients, all within 1 day, but at a higher rate in the aneurysmal group (40% versus 8%; P  = 0.07). A total of 88% of patients had modified Rankin scale score 0–2 at discharge, but at a significantly higher rate in nonaneurysmal patients (91% versus 40%; P  = 0.01). An underlying aneurysm, hydrocephalus, and symptomatic vasospasm were associated with poor functional status (odds ratio [OR] = 14.7 [2.1–104]; P  = 0.007, OR = 22.6 [4.2–123.5]; P <0.001, OR = 8.6 [1.06–69.88]; P  = 0.04), respectively. Conclusion “Benign” perimesencephalic subarachnoid hemorrhage pattern was associated with a ruptured aneurysm in 6.2% of patients, and 3.7% were detected only on cerebral angiogram. Underlying aneurysm, symptomatic vasospasm, and hydrocephalus were associated with lower rates of good clinical outcome. All hydrocephalus cases were symptomatic and occurred very early. Asymptomatic vasospasm alone was not associated with poor outcomes. Our findings suggest that patients with nonaneurysmal perimesencephalic subarachnoid hemorrhage without hydrocephalus can safely be managed with less strict monitoring and a shorter hospital stay.