Malhotra K, Zompola C, Theodorou A, et al. - According to this systematic review and meta-analysis, the etiology of spontaneous intracerebral hemorrhage (ICH) is unknown or cryptogenic in 1 out of every 7 patients in studies that use etiology-oriented classification and 1 out of every 4 patients in studies that do not use etiology-oriented classification. Despite the small ICH volume, the short-term mortality rate in undetermined ICH is high.

• There were 24 studies that included 15,828 patients with spontaneous ICH (mean age, 64.8 years; men, 60.8%).

• For hypertensive arteriopathy ICH, a pooled prevalence of 50% was noted; such estimate for undetermined ICH and cerebral amyloid angiopathy ICH was 18% and 12%, respectively.

• The volume of ICH in cerebral amyloid angiopathy ICH was the greatest, followed by hypertensive arteriopathy ICH and undetermined ICH.

• The rates of short-term mortality (within 3 months) and concomitant intraventricular hemorrhage were 33% and 38%, respectively, among patients with undetermined ICH.

• Subgroup analysis revealed a higher rate of undetermined ICH in studies that did not use an etiology-oriented classification.

• There was no difference in the rates of undetermined ICH between studies based on the completion of detailed neuroimaging.