Epidemiology and treatment of atraumatic subarachnoid hemorrhage over 10 years in a population-based registry

Introduction: Incidence of atraumatic subarachnoid hemorrhage (SAH) is decreasing over time and its treatment is changing. We reported epidemiologic data on aneurysmal (a-) and non-aneurysmal (na-) SAH over 10 years. Patients and Methods: Our prospective population-based registry included patients with first-ever SAH occurring from January 2011 to December 2020. Clinical and neuroimaging records were screened to evaluate the presence and location of intracranial aneurysms, to identify naSAH subtypes and to retrieve information on surgical treatments. Incidence rates were standardized to the 2011 Italian and European population. We also estimated 30-day and 1-year case-fatality rates after SAH. Multivariate hazard ratios for 30-days and 1-year fatality were estimated with Cox regression analysis. Results: 194 patients (60.8% women; mean age 62.5 +/- 16.0 years) were included (76.8% aSAH and 23.2% naSAH). The crude incidence rates per 100,000 person-years of SAH, aSAH, and naSAH were 6.5 (95% CI 5.6-7.5), 5.0 (95% CI 4.2-5.9), and 1.5 (95% CI 1.1-2.0), respectively, and remained stable over time. Compared to aSAH, naSAH patients had higher age (68.8 +/- 19.7 yearsvs 60.6 +/- 14.2 years; p = 0.012), lower cigarette smoking (17.9%vs 36.4%; p < 0.001) and higher atrial fibrillation (15.7% vs 2.8%; p = 0.005). SAH case-fatality rates within 30-days and 1-year were 28.4% (95% CI 21.4-36.9) and 37.1% (95% CI 29.0-46.7), respectively. The relative proportion of surgically treated patients did not change over time. Conclusion: We found a low and stable incidence of SAH over the 2011-2020 period. naSAH remained rare and deserves further investigation in larger prospective cohorts.