Modifiable Risk Factors for Subarachnoid Hemorrhage: Narrative Review With an Emphasis on Common Controversies and Epidemiologic Pitfalls.

Given the relatively low incidence, high prehospital death rate, substantial geographical differences, and complex disease origin (combination of genetic and environmental risk factors), epidemiologic research on subarachnoid hemorrhage (SAH) and its risk factors is challenging. In practice, we are more or less forced to exploit compromised study designs and nonrepresentative data in such circumstances where it is almost impossible to gather comprehensive data through an optimal design. For example, hospital-based patient cohorts, administrative data repositories, and short-term population-based studies from small geographical regions are often used to research the incidence, case fatality, and risk factors of SAH, regardless of their inherent and self-evident limitations.