Internal hernias after abdominal surgeries: MDCT features

As less-invasive treatments for small bowel obstruction, such as laparoscopic surgery or small incision therapy, have become common, there is a growing demand for preoperative assessment of the cause and location of the small bowel obstruction. Thus, the role of computed tomography (CT) in the evaluation of small bowel obstruction is expanding. CT imaging of internal hernias (IHs) has been extensively described and is well established; however, CT imaging of IH after abdominal surgeries is not well recognized because of their anatomical complexity. The aims of this pictorial review are (1) to evaluate the causes of internal IHs in relation to previous abdominal surgery (e.g., IH associated with Roux-en-Y reconstruction, Billroth II reconstruction, peritoneal adhesive band, perineal hernia, and IH after gynecological procedures), (2) to demonstrate the spectrum of imaging findings on multidetector CT (MDCT), and (3) explain the key features for CT diagnosis of IHs related to previous surgical procedures, with emphasis on the multi-planar reformation (MPR) image. We also demonstrate the dynamic changes in the progression of mesenteric strangulation revealed by CT. Understanding the imaging appearance on MDCT can help radiologists guide therapy for patients with a small bowel obstruction after abdominal surgery.