The Significance of the Angle between Superior Mesenteric Artery and Aorta in Spontaneous Isolated Superior Mesenteric Artery Dissection

Background The aim of this study is to assess the significance of the angle between superior mesenteric artery (SMA) and distal aorta in spontaneous isolated superior mesenteric artery dissection (SISMAD) by clinical and biomechanical analyses. Methods Thirty-seven patients with SISMAD (1 asymptomatic) and 148 controls (1:4 matched for age [mean 50.2 years], gender [92% male], and body mass index, and being ruled out for arterial disease) underwent aortic computed tomography angiography. SMA–distal aorta angle, measured on sagittal plane, was compared along with baseline characteristics (body mass index, smoking history, and comorbidities) between groups, and assessed as tool to evaluate SISMAD risk after stratification into 4 angle-interval categories. Flow analysis and fluid–structure interaction study were conducted based on patient-specific models with ultrasound-measured boundary conditions to further reveal the flow pattern and loading distribution in the 4 angle-interval categories. Results SISMAD patients versus controls had larger mean SMA–distal aorta angle (73 ± 19.8° vs. 50 ± 18.81°, P < 0.001), and more frequently smoking history (62% vs. 40%, P = 0.02) and hypertension (59% vs. 34%, P < 0.001), all multivariate predictors of no SISMAD (odds ratio 0.946 [95% confidence interval 0.927–0.966]; 0.415 [0.198–0.87]; and 0.252 [0.117–0.544], respectively). Odds ratio for SISMAD increased with increasing SMA–distal aorta angle (1, 10, 57, and 73 for <50°, 50–69°, 70–90°, and >90°, respectively; P < 0.05 for >70°). In silico study confirmed that larger angle is associated with higher stress in the arterial wall and higher oscillatory shear index in the vessel lumen at the SMA superior convex, where dissection commonly occurs. Conclusions Besides smoking history and hypertension, SISMAD was positively associated with a morphological parameter, the SMA–distal aorta angle. This might be due to the greater wall stress and oscillatory stress index in the arterial convex with a larger angle.