Clinico-Radiological Features of Acute and Chronic Superior Mesenteric Artery Occlusion (SMAO)

Superior mesenteric artery occlusion (SMAO) can present as acute mesenteric ischemia (AMI) with bowel necrosis or as mesenteric vascular narrowing with collateral formation, resulting in chronic mesenteric ischemia (CMI). The diagnosis is often delayed due to a low clinical index of suspicion, leading to a high mortality rate. We aimed to characterize the clinical and radiological features of SMAO. This retrospective study included 39 patients with SMAO reported on CT for 3 years. We compared the clinical features from medical records with imaging and intraoperative findings. The CT features of vessel occlusion, status of collaterals, bowel changes, and other intra-abdominal findings apart from involvement of other vessels (celiac, renal, aortic, neck vessels) were analyzed. Out of 39 patients, 12 had acute SMAO, and the remaining 27 patients had chronic SMAO and were sub-classified into Takayasu (n = 13) and non-Takayasu (n = 14) sub-groups. The acute group had proximal and distal occlusions equally and bowel gangrene changes but without collaterals, whereas chronic group had mainly proximal stenosis/occlusion and no bowel changes with well-formed collaterals. Involvement of other abdominal and peripheral vessels was noted in the chronic group (both Takayasu and non-Takayasu) but less in acute group patients. Early surgery in the acute group was associated with a better prognosis and CT-detected bowel ischemia changes correlated well with intraoperative findings. Acute and chronic SMAO have distinct features in terms of level and type of occlusion, bowel ischemic changes and collaterals. Takayasu arteritis may be a subset of chronic SMAO with associated changes, which warrant further elucidation.