Normal values of angle and distance between the superior mesenteric artery and aorta in Iraqi population: A single centre study

Introduction: The diagnosis of the superior mesenteric syndrome depends on measuring the distance and angle between the superior mesenteric artery (SMA) and aorta on CT scan in the presence of duodenal compression. Studies examining the normal range of these measurements are scarce and none of them was conducted on the Iraqi population. The aim of this study was to assess the values of aorto-SMA angle (AMA) and aorto-SMA distance (AMD) in asymptomatic patients to define the normal range in the Iraqi population and to compare it with the normal published range and different demographical values and body mass index (BMI).

Methods: A total of 333 patients referred to arterial phase CT examinations for reasons unrelated to gastrointestinal tract were recruited. On axial and reformatted sagittal-oblique images, the angle and the distance between SMA and aorta were measured at the location where the duodenum crosses.

Results: Both AMA and AMD had a wider range 10-147° and 4-44 mm, respectively, compared to the literature reported range. There was a significant reduction in AMA and AMD values in underweight participants (AMA, P < 0.001; and AMD, P = 0.014) and in female patients (AMA and AMD, P < 0.0001) and those who were younger than 20 (AMA, P = 0.014; and AMD, P = 0.001). A moderate correlation (r = 0.507, P < 0.0001) was found between AMA and AMD values. The correlation of BMI with AMD values was moderate (r = 0.46), and with AMA was weak (r = 0.23) (P < 0.0001).

Conclusion: Very low values of AMA and AMD can occur in normal asymptomatic patients without compressing the duodenum, which warrants further follow-up studies. Evaluating normal values of AMA and AMD in the Iraqi population can help in providing a reference for CT-based diagnosis of SMA syndrome.