ABSTRACT

Aneurysms are abnormal dilatations of a portion of the vascular wall (Figure 21.1). ey can occur at any age, but most commonly occur in the adult female population (Deshaies and Boulos 2011). ere are two types of intracranial aneurysms: fusiform aneurysms and ISAs. e rst are dilatations of a straight segment of artery without an obvious neck and oen occur in the basilar artery. e second are spherical in shape, have a neck, and commonly arise at the apex of a bifurcation located within the Circle of Willis (Figure 21.1) (Humphrey 2002; Kumar et al. 2007). ISAs are further classied by their diameter and size of neck. Small, large, and giant ISAs have diameters 4-10, 11-25, and >25 mm, respectively. Necks smaller than 4 mm are classied as small-necked, and necks greater than 4 mm as wide-necked ISAs (Murayama et al. 2003b). Fusiform aneurysms usually remain asymptomatic until they press on adjacent tissue. In contrast, ISAs oen remain asymptomatic until they rupture resulting in spontaneous subarachnoid hemorrhage (SAH), also known as a hemorrhagic stroke. Of these patients, approximately 35−50% die (Humphrey 2002; Szikora et al. 2006). Of those who do survive, 50% regain functional independence, while 30% are permanently disabled, and 20% require institutional care (Carod-Artal and Egido 2009).