Don’t be thrown for a loop: a review of internal hernias for the abdominal imager

Internal hernias are herniations of abdominal viscera, usually small bowel, through congenital or acquired openings of the peritoneum or mesentery. Congenital hernias may involve anatomic fossae such as the epiploic foramen as well as those related to abnormal peritoneal or mesenteric defects; these include left and right paraduodenal, transomental, transmesenteric, pericecal and broad ligament hernias. Acquired hernias are due to defects in the mesentery or peritoneum, usually resulting from prior surgeries, and include those associated with Roux-en-Y surgery as well as colorectal cancer resections. Internal hernias account for 5.8% of small obstructions. Obstructed internal hernias are considered surgical emergencies due to the high risk of bowel strangulation. This review summarizes the various types of congenital and acquired internal hernias, their relevant anatomy, embryology, associated surgical history and imaging appearance. We will also discuss a location-based approach to identifying internal hernias on CT, as well as complications and relevant signs, of which abdominal imagers should be vigilant.