Inference from clinical and fluid dynamic studies about underlying cause of spontaneous isolated superior mesenteric artery dissection

Purpose Due to increased use and improvements in diagnostic imaging studies, spontaneous isolated superior mesenteric artery dissection (SISMAD), which is a rare vascular event, has been reported to occur on a more frequent basis. Although there have been some anecdotal case reports describing the underlying pathology of SISMAD, the etiology of the majority of SISMAD is still poorly understood. The purpose of this study was to determine the underlying cause of SISMAD. Method From July 2001 to March 2010, 51 consecutive patients with SISMAD (symptomatic 39, asymptomatic 12) and 38 patients with combined aortic and superior mesenteric artery dissection (CASMAD) were identified in a single institution by retrospective investigations. Diagnosis was dependent on multi-detector helical computed tomography (CT) scan. To find clinical characteristics of SISMAD, we compared demographic, clinical, and lesion (site of entry tear, type, length) characteristics between the two groups. To find any flow dynamic abnormalities at the proximal segment of the superior mesenteric artery (SMA), we conducted flow dynamic studies using computational fluid dynamic models (V.12; ANSYS, Inc., Canonsburg, Pa). Streamline patterns and wall shear stress distributions were tested with computer simulation models using three different branching angles of SMA from the abdominal aorta. Results Compared to CASMAD, SISMAD was more common in men (90.2% vs 71.1%; P = .02), less frequently associated with hypertension (31.4% vs 65.8%; P = .001), and more frequently associated with intra-abdominal cancers (11.8% vs 0%; P = .036). In a fluid dynamic study using computational fluid dynamic models, we found abnormal mechanical stresses at the anterior wall around the convex portion of the SMA. Conclusion Development of SISMAD seems to be less likely the result of hypertension or connective tissue disease but more likely due to hemodynamic force caused by convex curvature.