Clinical and patho-anatomical factors affecting expansion of thoracic aortic aneurysms

Objective-To examine the expansion of aneurysmal aortic segments (greater t han or equal to 35 mm) and to assess the impact of clinical and patho-anato mical factors on aneurysm expansion. Design-87 consecutive patients (mean age 63.6 years, range 22-84 years) wer e studied using serial (six month intervals) computed tomographic or magnet ic resonance imaging to monitor progression of thoracic aortic aneurysms. A ortic diameter was measured at seven predetermined segments and at the site of maximum aortic dilatation (MAX). Results-780 segment intervals were identified. The median overall aneurysm expansion rate was 1.43 mm/year. This increased exponentially with incremen tal aortic diameter (p < 0.01) and varied by anatomical segment (p < 0.05). The presence of intraluminal thrombus (p < 0.01) but not dissection or cal cification was associated with accelerated growth. Univariate analysis iden tified thrombus (p < 0.001), previous stroke (p < 0.002), smoking (p < 0.01 ), and peripheral vascular disease (p < 0.05) as factors associated with ac celerated growth in MAX. Dissection, wall calcification, and history of hyp ertension did not affect expansion. beta Blocker treatment was not associat ed with protection. Multivariate analysis confirmed the positive effect of intraluminal thrombus and previous cerebral ischaemia, and the negative eff ect of previous aortic surgery on aneurysm growth. These findings translate d into a mathematical equation describing exponential aneurysm expansion. Conclusions-Aneurysmal thoracic aortic segments expand exponentially accord ing to their initial size and their anatomical position within the aorta. T he presence of intraluminal thrombus, atherosclerosis, and smoking history is associated with accelerated growth and may identify a high risk patient group for close surveillance.