Etiology and management outcomes of inferior mesenteric artery aneurysm.

Objective: Inferior mesenteric artery aneurysms (IMAAs) are extremely rare, and their natural history and treatment outcomes are poorly understood. Methods: We performed a retrospective review of consecutive patients with IMAAs treated at a multistate health system between November 2005 and August 2025. Demographics, etiology, imaging features, treatment, and outcomes were analyzed. Results: There were 15 patients (11 male; mean age, 66 ± 15 years), and all these patients were diagnosed on computed tomography angiography. Presentation was with nonspecific abdominal pain in nine patients (88%), symptomatic chronic mesenteric ischemia in one patient (6%), and shock owing to rupture in one patient (6%). The most common etiology was segmental arterial mediolysis (SAM) (n = 9 [60%]), followed by atherosclerosis (n = 6 [40%]). Ten patients (67%) were managed nonoperatively, and in these patients the mean IMAA diameter was 0.9 ± .4 cm. Over a median imaging follow-up of 42 months (range, 10-170 months), size remained stable with a mean IMAA diameter of 0.9 ± 0.4 cm. Surgical intervention was required in five patients (33%; mean IMAA diameter, 2.1 ± 0.4 cm). All three patients (20%) with atherosclerosis and celiomesenteric occlusion had an IMAA of >1.5 cm, consistent with poststenotic jet flow phenomenon. Indication for repair included IMAA enlargement to >2 cm, with symptomatic chronic mesenteric ischemia in one patient (6%). Procedures performed included aneurysm resection with aorta to IMA bypass with Dacron graft (n = 1), supraceliac aorta to celiac and superior mesenteric artery bypass with IMA aneurysmorrhaphy, and endovascular repair (covered stent placement, n = 1). In two patients (13%), the celiac and superior mesenteric artery were patent, and the IMAA was ligated (diagnosis at presentation with shock owing to IMAA rupture, etiology unknown; colectomy for recurrent diverticulitis and SAM with a 1.6-cm IMAA). There were no major postoperative complications or aneurysm-related death. At a median clinical follow-up of 50 months, two patients had died with a cause of death unrelated to IMAA. Conclusions: Inferior mesenteric aneurysms secondary to SAM are usually smaller at presentation and have a benign course. IMAA associated with celiomesenteric occlusion experience progressive enlargement owing to jet phenomenon hemodynamics and require repair. Repair is required for rupture or when the aneurysm diameter reaches ≥1.5 cm if the celiac and superior mesenteric artery inflow are intact.