Background: Abdominal aortic aneurysms are a major cause of death. Prediction of aneurysm expansion and rupture is challenging and currently relies on the simple measure of aneurysm diameter. Using MRI, we aimed to assess whether areas of cellular inflammation correlated with the rate of abdominal aortic aneurysm expansion.
Methods and results: Stable patients (n=29; 27 male; age, 70±5 years) with asymptomatic abdominal aortic aneurysms (4.0 to 6.6 cm) were recruited from a surveillance program and imaged using a 3-T MRI scanner before and 24 to 36 hours after administration of ultrasmall superparamagnetic particles of iron oxide (USPIO). The change in T2* value on T2*-weighted imaging was used to detect accumulation of USPIO within the abdominal aortic aneurysm. Histological examination of aneurysm tissue confirmed colocalization and uptake of USPIO in areas with macrophage infiltration. Patients with distinct mural uptake of USPIO had a 3-fold higher growth rate (n=11, 0.66 cm/y; P=0.020) than those with no (n=6, 0.22 cm/y) or nonspecific USPIO uptake (n=8, 0.24 cm/y) despite having similar aneurysm diameters (5.4±0.6, 5.1±0.5, and 5.0±0.5 cm, respectively; P>0.05). In 1 patient with an inflammatory aneurysm, there was a strong and widespread uptake of USPIO extending beyond the aortic wall.
Conclusions: Uptake of USPIO in abdominal aortic aneurysms identifies cellular inflammation and appears to distinguish those patients with more rapidly progressive abdominal aortic aneurysm expansion. This technique holds major promise as a new method of risk-stratifying patients with abdominal aortic aneurysms that extends beyond the simple anatomic measure of aneurysm diameter. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00794092.