What is the expected CT and MRI imaging appearance of the aorta after stent graft repair?
CT is used postoperatively to assess for stent placement (location, stent patency, aorta size, and any associated complications). In particular, it is of utmost importance to document any increase or decrease in the size of the aorta, including the proximal and distal aortic necks. Following stent-graft repair, a follow-up CT is performed at 1st and 4th week followed by a 6-month scan, a 1-year scan, and then scans annually thereafter. Periaortic changes (aortic wall thickening, atherosclerosis, and effusion), perigraft leak, and/or aortic dissection may be seen immediately following the procedure.
MRI is usually not performed after stent placement because the artifacts caused by stainless steel stents will generally obscure the aneurysm sac. However, stent-grafts composed of nitinol or elgiloy do not cause appreciable artifact, and for these patients, contrast-enhanced MRA has a higher sensitivity for endoleak detection compared to CTA. With respect to the MRI findings following stent-graft repair, the early normal postoperative changes are characterized by a perigraft collar of low-intermediate T1-weighted signal intensity and high T2-weighted signal intensity consistent with the perigraft fluid. Two to three months postoperatively, the perigraft collar is characterized by low signal intensity fibrotic tissue.