[Postoperative evaluation of vascular bifurcation prostheses by means of helical CT]

The dilatation of the vascular grafts is a well known phenomenon. It is usually evaluated by means of ultrasounds or, in selected cases, by CT scans or MRI; nevertheless its characteristics are far beyond to be fully recognized. Following our promising preliminary experience with helical CT as sole preoperative imaging for AAA, we have evaluated its reliability in the postoperative follow-up. We have studied 12 patients with aorto-iliac and 11 with aorto-femoral bypass for AAA, with a follow-up ranging between 1 and 3 years. A helical CT acquisition was performed during a single breath-holding with a 5-mm slice thickness, thus resulting in a 30 cm z-axis coverage. Axial images were reconstructed at 2-mm increments and used to generate high quality multiplanar reformatted (MPR) and three-dimensional (3D) surface rendered images. For each patient we evaluated the characteristics of the graft, the maximal diameters and the wall modifications. The average expansion was 28% at 1 year, stable at 2 years and then increased up to 44% at 3 years. Considering the different types of Dacron grafts, the dilatation was ranging between 22% and 46% (21 cases). The mean expansion was 31.3% and 29.5% for the trunk and for the branches of the graft respectively. No perigraft seroma nor anastomotic aneurysms were detected. A peculiar observation, both with and without contrast medium injection, was that all the grafts made on Dacron were not anymore depictable from the aortic wall after 1 year; the contrary was observed for the ePTFE grafts.