Morphology of Small Abdominal Aortic Aneurysms Should be Considered before Continued Ultrasound Surveillance

Background: To evaluate abdominal aortic aneurysm (AAA) morphology in a cohort of patients presenting with ruptured AAA (rAAA) and to explore if aneurysms with diameters below the recommended threshold for elective repair (<55 mm) have some distinctive morphological characteristics. Methods: All patients diagnosed with rAAA using computed tomography (CT) scans between January 2006 and June 2013 were eligible for this study. Where CT scans of acceptable quality were available, images were reconstructed in a dedicated three-dimensional vascular workstation for evaluation of aneurysm diameters and morphology. All morphological characteristics were defined according to the reporting standards for endovascular aortic aneurysm repair. Additionally, fusiform AAAs were defined as aneurysms involving the whole circumference of the aortic wall and saccular AAAs as spherical aneurysms involving only a portion of the aortic circumference. Results: A total of 248 patients were identified. Of those, 83% (n = 206) had high -quality CT scans available and were included in the study. Patients were on average 75 years old and 85% were men. Mean aneurysm diameter was 76 14 mm and 95% (n = 197) had fusiform morphology. Six percent (n = 12) were <55 mm and those included all saccular aneurysms in women (n = 3) and 22% of saccular aneurysms in men (n = 2). The remaining saccular aneurysms (n = 4) were small with a maximal diameter of 56 mm. Aneurysms <55 mm had less angulated proximal necks than their larger counterparts (P < 0.01). No other morphological differences were found between the groups. Conclusions: Ruptured aneurysms are often large and the >= 55 mm threshold for elective repair is probably appropriate. However, approximately 6% of rAAAs are <55 mm, with a significant portion being saccular, especially in women. Morphological assessment of AAAs with CT scans should be considered in small aneurysms (40-55 mm), particularly in women, to exclude saccular morphology before continued ultrasound surveillance.