What Is an Aneurysm and What Is a Subarachnoid Hemorrhage

Abstract

Aneurysms are bulges of the intracranial arteries caused by local weakness of the arterial wall. They are often referred to as saccular or berry aneurysms because of their shape and to discriminate these aneurysms from the much rarer dissecting aneurysms, which are caused by a tear in the aneurysm wall. Aneurysms are usually located at the basal intracranial arteries in the subarachnoid space. Most aneurysms go unnoticed, unless they are very large, rupture, or are incidentally found during brain imaging. Rupture of an aneurysm gives rise to a subarachnoid hemorrhage, which may extend into the brain parenchyma or ventricular system. A subarachnoid hemorrhage from an intracranial aneurysm is a subset of stroke that carries a high risk of death or permanent disability and usually occurs at relatively young age. There are many more causes of subarachnoid hemorrhage than rupture of an aneurysm, with trauma being the most common, and the most appropriate term would be aneurysmal subarachnoid hemorrhage, but for the sake of simplicity and because it is often used as such, we will refer to a hemorrhage from a (presumed) rupture of an intracranial aneurysm as subarachnoid hemorrhage. Similarly, we will use the term aneurysm for intracranial saccular aneurysms. This chapter describes the prevalence and risk of rupture of intracranial aneurysm, the incidence and risk factors for subarachnoid hemorrhage, the clinical syndrome of subarachnoid hemorrhage and case fatality and dependency rates after subarachnoid hemorrhage.