**4. Epidemiology**

The true incidence and prevalence of aortic aneurysms is difficult to ascertain due to the silent nature of this disease [7]. In a computed chest tomography (CT) study the prevalence of asymptomatic thoracic ascending aneurysm was 0.16% [8]. In a different study the prevalence was noted to be 0.34% [9]. The incidence and prevalence of aneurysms tend to differ between studies due to different aortic dimension cut-offs. The majority of studies did not include aortas between 4 and 5 cm [7]. The annual incidence according to two studies was estimated to be in the range of 5.6 and 10.4 cases per 100,000 patient-years [10, 11]. Thoracic aneurysms are more common in men greater than 60 years of age [7].

Abdominal aortic aneurysm is predominantly a disease of men [12–15]. The incidence rises with age. In screening studies its prevalence is estimated at 4–8%. The incidence of new cases of abdominal aortic aneurysms in the western population is estimated at 0.4–0.67% [7].

The true incidence and prevalence of HIV associated aneurysms remains understudied. The incidence of symptomatic vasculitis in HIV-infected patients is reported to be 1% [16].
