Pregnant Women After Bariatric Surgery: Diagnostic Accuracy of Magnetic Resonance Imaging for Small Bowel Obstruction

Background: Small bowel obstruction (SBO) is a late complication of Roux-en-Y gastric bypass (RYGB). In non-pregnant patients, computed tomography (CT) is the first choice of imaging. During pregnancy, magnetic resonance imaging (MRI) is preferred to limit exposure to ionizing radiation. However, literature regarding the diagnostic accuracy of MRI for SBO is scarce.

Objective: To describe the diagnostic accuracy of MRI for SBO during pregnancy.

Methods: Pregnant women with RYGB suspected for SBO who presented at our center between September 2015 and April 2020 and who received an MRI scan (index) and underwent surgery (reference) were included. Original reports were retrospectively evaluated. Available MRI scans were structurally reinterpreted by two experienced radiologists. Statistical analysis included sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and Cohen's kappa.

Results: Twenty-seven original MRI reports were included. Twenty-four (89%) MRIs were of good quality. Sensitivity was 67% (confidence interval (CI) 0.43-0.85), specificity 67% (CI 0.13-0.98), PPV 93% (CI 0.66-0.99), and NPV 22% (CI 0.04-0.60). MRI was unable to detect SBO in 1 out of 3 patients. The presence of swirl sign, SBO sign, or clustered loop sign increases the likelihood of SBO. The interobserver agreement was overall wide, with the highest score for swirl sign (κ 0.762).

Discussion: MRI is a safe and feasible alternative for CT. The value is doubtful as diagnostic accuracy shows wide ranges with considerable variability in the interobserver agreement. We would cautiously advise to perform MRI in case of a mild clinical presentation, but in case of a severe clinic, the diagnostic laparoscopy should remain the gold standard.