Size and location of thrombus in intact and ruptured abdominal aortic aneurysms

Abstract

This study compared the volume and morphology of intraluminal thrombus (ILT) in intact and ruptured abdominal aortic aneurysms (AAAs). ILT volume in 67 intact AAAs and in 31 ruptured AAAs was assessed by using computed tomography (CT) angiography to measure the major and minor diameter of the outer wall and lumen of AAA as outlined by contrast at multiple sites. ILT thrombus morphology was recorded by AutoCAD 2000 software. Four equidistant images traced from the CT scan were recorded along the length of AAA. Thrombus volume was categorized as anterior-eccentric if the calculated area of thrombus was greater anteriorly, posterior-eccentric if greater posteriorly, eccentric-equal if the difference between the anterior and posterior thrombus was <or=10%, and no thrombus. Patients were well matched for age, gender, and other demographic variables except hypertension, which was significantly higher in ruptured AAA group ( P = .018). Ruptured AAAs were larger in diameter compared with intact AAAs (7.3 +/- 1.7 cm vs 6.0 +/- 1.2 cm, P = .0002). ILT volume was greater in ruptured AAAs (148.9 +/- 90.4 cm 3 ) compared with intact AAAs (92.1 +/- 75.6 cm 3 , P = .0031). However, the ILT volume/aneurysm volume ratio was similar in the two groups (0.49 +/- 0.19 in intact AAAs, 0.47 +/- 0.18 in ruptured AAAs; P = .8). Two patients in intact AAA group and three patients in the ruptured AAA group did not have ILT. Eccentric thrombus was present in 65 of 67 in the intact group and in 28 of 31 in the ruptured AAA group. Eccentric-anterior thrombus was predominant in both groups (46 of 67 in intact AAAs; 14 of 31 in ruptured AAAs). Thrombus location was statistically similar in both groups ( P = .101). Ruptured AAAs are larger in diameter and have a greater volume of thrombus compared with intact AAAs. However, there was no difference in the thrombus volume/aneurysm volume ratio in the two groups. In both intact and ruptured AAA groups, the thrombus was usually anterior and eccentric.