Internal hernia

Congenital internal hernias

• Abnormal retroperitoneal fixation of the mesentery resulting in anomalous intestinal position (mesocolic or paraduodenal hernias)
  • Mesocolic: the small intestine herniates behind the mesocolon. Result from abnormal rotation of the midgut. Categorised as left or right.
    • Right: most of small intestine remains to the right of SMA, and becomes trapped behind the mesentery of the right colon. Ileocolic, right colic and middle colic vessels lie within the anterior wall of the sac, and SMA courses along the medial border of the neck of the hernia. Treat by incising the lateral peritoneal reflections along the right colon, with reflection of the right colon and caecum to the left.
    • Left: caused by in utero herniation of small bowel between IMV and posterior parietal attachments of the descending mesocolon to the retroperitoneum. Treat by incising the peritoneal attachments and adhesions along the right side of IMV, with reduction of the herniated small intestine from beneath IMV.
  • Paraduodenal hernias usually present as SBO.
    • Exceedingly rare
    • Paraduodenal recesses
      • To the left of D-J flexure, sometimes present
      • Small evagination of peritoneum beneath the upper end of IMV
    • An incarcerated hernia may obstruct and thrombose IMV
• Abnormally large internal foramina or fossae (e.g. foramen of Winslow, supravesical hernia)
• Incomplete mesenteric surfaces with the presence of an abnormal opening through which the intestine herniates (e.g. mesenteric hernia)
  • Most common location is near the ileocolic junction, and sometimes defects in the sigmoid mesocolon

Acquired internal hernias

• Usually result from inadequate closure/dehiscence of mesenteric defects created during a gastrojejunostomy, colostomy, ileostomy or bowel resection