Internal Hernia After Bariatric Surgery
An internal hernia is a loop of bowel slipping through a gap created inside the abdomen during gastric bypass; it is the commonest cause of bowel obstruction after keyhole bypass surgery and needs urgent assessment.
Plain English
Patient-Friendly Explanation
An internal hernia is different from the hernia most people picture, the bulge under the skin. It happens inside the abdomen. When a surgeon performs a gastric bypass they rearrange the small intestine into a Y shape, and in doing so they create potential gaps between loops of bowel and their supporting membranes. Usually the surgeon closes these gaps, but a gap can reopen, or a loop of bowel can slip through one that was left open. The bowel then becomes trapped, twists on itself, and its blood supply is at risk. This is the commonest cause of bowel obstruction after a laparoscopic gastric bypass, and it is more common after keyhole surgery than after open surgery precisely because keyhole surgery leaves fewer internal adhesions - scar tissue that would otherwise hold the bowel in place. Reported rates after laparoscopic gastric bypass range from about half a per cent to nine per cent, and early series that did not routinely close the gaps reported rates as high as fourteen per cent. The two usual sites are named after the surgeon Petersen, describing the space behind the limb of bowel carrying food, and the gap at the join lower down where the two intestinal limbs are connected. The difficulty is that symptoms can be vague and can come and go. A person may have episodes of severe cramping pain in the upper or middle abdomen, sometimes with nausea and vomiting, that settle on their own before returning. That pattern is dangerous to dismiss, because an internal hernia can progress to strangulation in a matter of hours. A CT scan of the abdomen is the key test and shows characteristic twisting of the blood vessels, sometimes called the swirl sign. Treatment is an operation to reduce the trapped bowel and close the defect. Meticulous closure of these defects at the original operation has cut the rate from around thirteen per cent to about one per cent in large series, so the risk today is lower than the early figures suggest.
Medical
Clinical Definition
Internal hernia after laparoscopic Roux-en-Y gastric bypass results from herniation of small bowel through a mesenteric or mesocolic defect created during the index operation. Two sites predominate: the Petersen defect, the potential space between the mesentery of the alimentary (Roux) limb and the transverse mesocolon, and the jejunojejunostomy mesenteric defect; a mesocolic defect is a third site when a retrocolic Roux limb is used. Reported incidence after laparoscopic Roux-en-Y bypass is approximately 0.5-9 per cent, with rates up to 14.4 per cent in early laparoscopic series before routine closure of mesenteric defects became standard; incidence is higher after laparoscopic than open bypass, reflecting the reduced adhesion formation that would otherwise splint the bowel. Internal hernia is the commonest cause of small bowel obstruction following laparoscopic gastric bypass, whereas adhesions remain the dominant cause after open surgery. Presentation is often intermittent at first - postprandial colicky epigastric or periumbilical pain, nausea and vomiting that may resolve spontaneously - which carries a risk of diagnostic delay; pain out of proportion to examination findings and the absence of fever should raise suspicion. Contrast-enhanced CT is the investigation of choice, with findings that include the mesenteric swirl sign, clustered and converging mesenteric vessels, small bowel dilatation, and in advanced cases reduced bowel wall enhancement or pneumatosis indicating ischaemia. Treatment is surgical and urgent: reduction of the herniated bowel with closure of all defects, laparoscopically or by laparotomy depending on bowel viability and adhesions, with resection reserved for non-viable segments. Prophylactic closure of mesenteric defects using running non-absorbable suture substantially reduces risk; in a series of 1,927 patients with a mean follow-up of 15 years, the incidence fell from 12.9 per cent with interrupted sutures to 1.05 per cent with running non-absorbable suture plus a purse-string at the jejunojejunostomy, although a small residual risk persists. Presentation may occur many years after surgery and should be considered in any post-bypass patient with unexplained abdominal pain or vomiting.
Key Insight
Why It Matters
Severe or recurring cramping abdominal pain in anyone who has had a gastric bypass is a surgical emergency until proven otherwise, because an internal hernia can twist and strangle the bowel within hours even though the early episodes keep settling.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: October 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
