The significance of endograft geometry on the incidence of intraprosthetic thrombus deposits after abdominal endovascular grafting.

OBJECTIVES: To examine the incidence and risk factors of intraprosthetic thrombotic deposits in abdominal aortic endografts.

METHODS: The clinical records of 51 patients (44 males; mean age 76.3 years, range: 63-90 years) with abdominal aortic aneurysm treated with transfemoral implantation of bifurcated stent graft between the years 2002 and 2008 were retrospectively reviewed. Patients underwent three-phase helical computed tomographic (CT) examinations at 1-, 3-, 6- and 12-month intervals and then annually. The formation of intraprosthetic thrombus associated with use of anti-platelet, preoperative mural thrombus in the aneurysm, ratio of cross-sectional area between the mainbody and bilateral limb grafts and length of mainbody were evaluated.

RESULTS: Over a 10-month mean follow-up, intraluminal deposits of thrombotic material were observed in eight of 51 patients (15.6%, 95% confidence interval: 8.2-28). The first signs of thrombus formation occurred on average 9.8 months after endografting (range: 1-24 months). Intraprosthetic thrombotic deposits was not related to preoperative mural thrombus formation (p=0.38) or postoperative anti-platelet or anticoagulation medication (p=0.40). However, it was significantly related to the ratio of the cross-sectional area between the mainbody and the bilateral limb grafts and the length of mainbody (p=0.04 and p=0.01). There were three graft limbs occlusion owing to kinking with no intraprosthetic thrombus detected on CT scans taken prior to occlusion. One patient developed distal left proximal superior femoral artery embolisation 4 months after detectable intraprosthetic mainbody thrombus in a CT scan follow-up. In no case did the thrombotic deposits clear completely from the prosthesis lumen during follow-up.

CONCLUSIONS: This short experience demonstrates that incidentally found thrombotic deposits in abdominal aortic endografts are common. The deposition of thrombus is mostly influenced by the geometry of the aortic stent graft with wider mainbody diameter coupled with smaller limb grafts and longer mainbody graft. Most of these thrombi are clinically silent and require no additional treatment.