Clinical Associations and Causes of Convexity Subarachnoid Hemorrhage

Background and Purpose— It has been previously found noted that ≈15% to 20% of subarachnoid hemorrhage (SAH) is nonaneurysmal. Nontraumatic convexity SAH (cSAH) is increasingly recognized. Data concerning incidence and associations are scant. Methods— We identified all SAH-coded cases from South Australian public hospitals between January 2005 and July 2011. Electronic discharge summaries were reviewed, and cases of cSAH were ascertained. Clinical and radiological features were recorded, and pathogenesis was assigned. Results— Of 742 cases with SAH, 41 (6%) cases were cSAH, giving a minimum population annual incidence of 5.1 per million (95% confidence interval, 3.7–7.0). Median age was 70 years (interquartile range, 48–79). Commonest causes were cerebral amyloid angiopathy (39%), reversible cerebral vasoconstriction syndrome (17%), cerebral venous sinus thrombosis (10%), large-vessel stenotic atherosclerosis (10%), and posterior reversible encephalopathy syndrome (5%). No cause was identified in 20% (mostly elderly patients with incomplete evaluation). Most (63%) presented with transient neurological symptoms. Many (49%) were misdiagnosed as transient ischemic attacks and treated inappropriately with antithrombotics. Conclusions— cSAH comprises a significant proportion of SAH. Commonest causes are cerebral amyloid angiopathy in the elderly and reversible cerebral vasoconstriction syndrome in the young, but differential diagnosis is broad. Misdiagnosis is common and leads to potentially harmful treatments.