Lack of thrombus organization in nonshrinking aneurysms years after endovascular abdominal aortic aneurysm repair.

OBJECTIVE

During endovascular abdominal aortic aneurysm repair (EVAR), blood is trapped in the aneurysm sac at the moment the endograft is deployed. It is generally assumed that this blood will coagulate and evolve into an organized thrombus. It is unknown whether this process always occurs, what its time span is, and how it influences aneurysm shrinkage. With magnetic resonance imaging (MRI), quantitative analysis of the aneurysm sac is possible in terms of endoleak volume as well as unorganized thrombus volume and organized thrombus volume. We investigated the presence of unorganized thrombus in nonshrinking aneurysms years after EVAR.

METHODS

Fourteen patients with a nonshrinking aneurysm without endoleak on computed tomography/computed tomography angiography underwent MRI with a blood pool agent (gadofosveset trisodium). Precontrast T1-, precontrast T2-, and postcontrast T1-weighted images (3 and 30 minutes after injection) were acquired and evaluated for the presence of endoleak. The aneurysm sac was segmented into endoleak, unorganized thrombus, and organized thrombus by interactively thresholding the differently weighted images. The classification was visualized in real-time as a color overlay on the MR images. The volumes of endoleak, unorganized thrombus, and organized thrombus were calculated.

RESULTS

Median time after EVAR was 2 years (range, 1-8.2 years). The average aneurysm sac volume of the patients was 167 ± 107 mL (mean ± standard deviation). Nine patients had an endoleak on the postcontrast T1-w images 30 minutes after injection. On average, the aneurysm sac contained 78 ± 61 mL unorganized thrombus, which corresponded to 51 ± 21 volume-percentage, irrespective of the presence of an endoleak on the blood pool agent enhanced MRI images (independent t-test, P = .8).

CONCLUSIONS

In our study group, half of the nonshrinking aneurysm sac contents consisted of unorganized thrombus years after EVAR.