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With the introduction of screening programmes for abdominal aortic aneurysm (AAA) more individuals are being identified with a subaneurymal aorta (SAA; diameter 25-29mm). More recent data indicate that these aortas may not be as harmless as previously thought, but there is, however, no general agreement on how SAA should be managed.

The aims of this thesis were to study men with screening detected SAA, regarding: (I) prevalence, risk factors and comorbidities; (II), the long-term natural course regarding development to AAA ≥30mm, in particular the progression to AAA ≥55mm, to assess the AAA repair rate, turn down, and mortality rates; (III) the association between aortic morphological baseline factors; (SAA diameter, aortic index related to height and body surface area as well as relative aortic diameter to proximal aorta) and the risk for later progression to AAA ≥55mm; and (IV) describe health utility (HU) values and compare them in men with screened AAA, SAA and in men with normal aortic diameters.

There was a marked similarity in the risk factor profile between men with SAA representing 2% of the screening population and men with AAA with smoking as the most important risk factor, with an incremental association between smoking and disease severity. Most SAAs eventually progress to an AAA ≥30mm, of which 30% eventually reach the threshold for AAA-repair within 10 years. A follow-up policy with an ultrasound scan after five years can safe and effectively identify those at risk of developing clinically relevant AAAs, and should be considered for anyone with reasonably good life expectancy. Baseline SAA diameter, aortic size index, and aortic height index were all independently associated with progression to AAA ≥55mm, with aortic size index as the strongest predictor, whereas relative aortic diameter was not. These morphological factors may be considered for stratification of follow-up at initial screening. At baseline screening, HUs were similar between men with AAA, SAA, and normal aortas. Compared to SAAs and controls, lower health utility scores were observed in men with AAA after five years, most likely associated with higher frequency of smoking and comorbidities.