Incremental value of the perivascular fat attenuation index surrounding the superior mesenteric artery on non-contrast CT for predicting SMA abnormalities in patients with acute abdominal pain.

OBJECTIVE: To evaluate the predictive value of the perivascular fat attenuation index (FAI) surrounding the superior mesenteric artery (SMA) on non-contrast CT for SMA abnormalities in acute abdominal pain and FAI's incremental utility in risk models. METHODS: This retrospective study included 262 acute abdominal pain patients (77 with SMA abnormalities, 185 controls) admitted between January 2020 and December 2025. All underwent non-contrast and contrast-enhanced CT within 48 h. Independent predictors were identified via univariate and multivariate logistic regression. The maximum area under the curve (AUC) was obtained through receiver operating characteristic analysis, and the predictive performance of models was comprehensively evaluated using net reclassification (NRI) and integrated discrimination improvement (IDI). Decision curve analyses (DCA) and calibration curves were used to evaluate the clinical utility and calibration of the models. RESULTS: Independent predictors of SMA abnormalities were smoking (OR = 10.452, 95% CI: 2.528-43.219), elevated high-sensitivity C-reactive protein [hsCRP] (OR = 1.012, 95% CI: 1.001-1.023), increased SMA diameter [SMA-d] (OR = 4.414, 95% CI: 2.758-7.062), and high FAI (OR = 1.092, 95% CI: 1.053-1.132; all P < 0.05). Four models were constructed: Model A (smoking + hsCRP), Model B (Model A + SMA-d), Model C (Model A + FAI), and Model D (Model A + SMA-d + FAI). Model D achieved the highest AUC (0.970; 95% CI: 0.952-0.988), outperforming Model A (AUC = 0.734), Model B (AUC = 0.945), and Model C (AUC = 0.878; all P < 0.001). Versus Model A, Model D showed superior NRI (0.780) and IDI (0.573; both P < 0.001). Model B outperformed Model C in incremental value (NRI: 0.657 vs. 0.457; IDI: 0.460 vs. 0.295; all P < 0.001) when each was compared with Model A. DCA confirmed Model D provided maximal net clinical benefit (threshold probability: 0%-91%). The Model D nomogram demonstrated excellent calibration. CONCLUSION: A high FAI was independently associated with SMA abnormalities, although its incremental predictive value was lower than that of SMA-d. Thus, FAI might serve as a complementary imaging biomarker rather than a stand-alone diagnostic marker. Integrating smoking status, hsCRP, SMA-d, and FAI might improve early risk stratification based on non-contrast CT and support timely diagnostic evaluation.