Superior Mesenteric Artery Syndrome: A Diagnostic Conundrum

Abstract

Introduction: Superior Mesenteric Artery Syndrome (SMAS) is a rare, controversial disease resulting from compression of the duodenum by the superior mesenteric artery [Fig. 1]. Current diagnostic criteria include symptoms of small bowel obstruction and a narrowed aortomesenteric (AM) angle (< 25 deg) or AM distance (< 8mm) at the level of the duodenum [Fig. 2]. In the absence of a complete understanding of the pathophysiology of SMAS, many question the specificity of these criteria. Our aim was to determine how accurately current criteria diagnose true SMAS and identify variables distinguishing true SMAS cases from those with an alternate diagnosis.Figure 1Figure 2Methods: We conducted a dual-center retrospective chart review from 2/2000 to 2/2015. All patients met SMAS criteria as above based on bowel obstruction symptoms and abdominal CT findings. Two radiologists independently verified AM distances/angles. In ‘unlikely' SMAS patients, treating physicians determined a more likely diagnosis versus ‘true' SMAS in which other diagnoses were excluded. Results: For 51 patients meeting SMAS criteria, mean age was 38.5 years (SD 16.1), 68.6% were female. At presentation, mean BMI was 20.1kg/m2 (SD 3.9), AM distance was 7.3mm (SD 2), and AM angle was 8.5deg (SD 3.3). 70.6% underwent treatment (66.7% medical therapy only, 3.9% surgical treatment) and 80.4% of all patients noted symptom resolution during follow-up [Table 1]. In 32 (62.7%) cases, a physician had specifically considered and dismissed SMAS as the cause of the patient's symptoms in favor of a more likely diagnosis (PPV with diagnostic criteria = 37.3%), such as opioid-induced bowel dysfunction (15.6%), enteritis (15.6%), and mechanical small bowel obstruction (12.5%). ‘True' SMAS patients more likely reported recent rapid weight loss (OR 4.8, 95% CI 1.4-17.1), tobacco use (OR 3.5, 1.1-11.6), and HCV infection (OR 14.3, 1.6-131). There were no significant differences in AM distances, angles, or symptom duration between the two groups.Table 1: Clinical Characteristics of Patients Meeting Diagnostic Criteria for SMASConclusion: In our experience, current SMAS diagnostic criteria overestimate SMAS. There is no correlation with severity of AM distances and angles and having true SMAS. Aside from recent rapid weight loss, tobacco use, and HCV infection, few predictive factors distinguish those who likely have another competing diagnosis. In the absence of more specific diagnostic criteria for SMAS, clinical judgment is necessary to rule out more likely diagnoses.