Internal Hernias: A Rare But Cannot Miss Diagnosis

Authors: Nicholas Alsofrom, MD (@AlsofromNick, EM Resident Physician, University of Vermont Medical Center) and Katie Wells, MD (@KatieWellsMD, EM Attending Physician, University of Vermont Medical Center) // Reviewed by: Marina Boushra, MD (@BoushraMarina); Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit)


A 47-year-old woman presents to the emergency department with three days of nausea, vomiting, and generalized abdominal pain. Her medical history is notable for diabetes, hypertension, and obesity status post Roux-en-Y gastric bypass. On abdominal examination, she is diffusely tender without guarding, rebound, or rigidity. CT scan demonstrates a closed-loop small bowel obstruction, evidence of mild stranding and multiple air fluid levels. Her labs are notable for a leukocytosis of 14 and a lactic acid of 2.2.


Internal hernias occur when bowel herniates through a congenital or iatrogenic mesenteric defect (Figure 1).  While rare, internal hernias have been linked to 0.6 – 5.8% of small bowel obstructions (SBOs). 1 This internal herniation can occur in a variety of locations and they can be further classified as right or left paraduodenal, through the foramen of Winslow, pericecal, sigmoid-mesocolon-related, transmesenteric, transomental, supravesical or a pelvic hernia (Figure 2). Historically, paraduodenal hernias were the most common; more recently, due to the increase in Roux-en-Y procedures, transmesenteric internal hernias have now surpassed them in incidence.2 In fact, approximately 42% of SBOs after gastric bypass surgeries are secondary to internal hernias.3 Symptomatic internal hernias have a high rate of strangulation and are associated with a mortality rate exceeding 50%.4 Given the high risk of significant morbidity and mortality if this diagnosis is missed, this diagnosis should be seriously considered in the right clinical situation, in particular patients who have undergone Roux-en-Y gastric bypass.

History and Exam

Consider the diagnosis of an internal hernia in patients presenting with SBO or symptoms of intermittent obstruction. Although internal hernias can occur in patients with a surgically naïve abdomen, more commonly, patients will have a history of laparoscopic surgery, particularly a surgery which utilizes the Roux-en-Y enteral anastomosis technique.2 This technique is classically seen in gastric bypass and liver transplant. Do not forget to consider this diagnosis in pregnant patients who are status post gastric bypass.5 Internal hernias do not present homogenously; they can present as vague abdominal or epigastric pain or as an acute abdomen.6 Most patients will present with symptoms of intermittent or persistent SBO and can also have associated abdominal distention, nausea, constipation, and vomiting. The exam can range from a benign abdomen to overt peritonitis. The ambiguity in the history and exam makes the diagnosis of internal hernia challenging—likely contributing to its high mortality rate. In general, it is best to have a low threshold for additional workup when evaluating patients with a concerning medical history.

ED Evaluation and Testing

In a patient with a clinical history or exam concerning for an internal hernia, an urgent CT scan of the abdomen/pelvis with IV contrast is the test of choice. Although there is limited data on the sensitivity and specificity of CT in the diagnosis of internal hernias specifically, one review suggests CT imaging has a sensitivity and specificity for SBO of 94-100% and 90-95% respectively.2 This makes CT a great choice for diagnosing internal hernias, as those causing SBO are often the ones associated with a high mortality.2 If a closed loop SBO is seen on CT, internal hernia should be high on the differential. Additionally, dilated loops of bowel in a ‘sac-like appearance’ can sometimes be seen and should further increase clinical suspicion. If strangulation is present, engorged disconnected mesenteric vessels may be noted within the closed loop obstruction.2 Finally, in patients with a history of Roux-en-Y procedures, the “mesenteric swirl sign” (Figure 3) has been described as the most sensitive and specific finding, 78-100% and 80-90% respectively, for diagnosing an internal hernia.7 If any of this is seen on CT scan, immediate surgical consult should be initiated.

An upper GI series with small bowel follow-through could also be considered if a CT scan is contraindicated; this would demonstrate SBO.8 In pregnant patients, an abdominal x-ray can be considered. The x-ray may show multiple air-fluid levels with an absence of air in the large bowel; this may be enough to prompt a diagnostic laparotomy if high clinical suspicion is high enough. If the x-ray is non-diagnostic, CT or MRI could be considered, this decision should be made in conjunction with general surgery and obstetrics. Notably, internal hernias are often intermittent and if imaging is performed while the patient is asymptomatic, the tests may be non-diagnostic. Labs such as leukocytosis greater than 18,000 or lactic acidemia suggest a gangrenous or ischemic bowel; unfortunately, neither is sensitive enough to rule out bowel ischemia. Recent meta-analysis using varying lactate cut offs suggest an elevated lactic acid has a sensitivity of 86% for diagnosing bowel ischemia, so while this can bolster suspicion for the diagnosis, it should not be used to rule out this life-threatening disease.9


Some internal hernias may not be identified until surgical exploration.10 If an internal hernia is suspected in a hemodynamically unstable patient with signs of peritonitis on exam, surgical consultation and exploration should not be delayed for diagnostic studies. Imaging, specifically a CT scan, is often the crux for developing a compelling diagnosis and should be initiated early in a patient with a story suspicious for an internal hernia. If an internal hernia is identified or strongly suspected as the cause of SBO, non-surgical medical management is not appropriate and surgical consultation should be initiated immediately. Finally, the mortality of internal hernias is correlated to the degree of intestinal necrosis, which leads to sepsis and multi-organ failure. If an internal hernia causing bowel strangulation is suspected, broad spectrum antibiotics covering intra-abdominal pathogens is recommended.


  • Consider internal hernia as a cause for small bowel obstruction in any patient. Those with a history of surgeriesrequiring Roux-en-Y technique such as gastric bypass or liver transplant are at higher risk, but internal hernias can occur in the surgically naïve patient as well, particularly if there is concern for a mechanism causing a mesenteric injury such as blunt abdominal trauma causing a mesenteric tear.11
  • CT scan with intravenous contrast is the first line imaging modality in stable patients with suspected internal hernia. In the setting of Roux-en-Y procedures, the most sensitive and specific sign is the mesenteric swirl. However, any SBO, particularly a closed loop SBO, should raise concern for the diagnosis.
  • If internal hernia is strongly suspected or confirmed, urgent surgical consultation and exploration is required due to the high prevalence of bowel strangulation and infarction.
  • Sepsis is a large contributor to mortality associated with any type of bowel ischemia; if intestinal necrosis or ischemia is suspected broad-spectrum antibiotics should be administered early.

References/Further Reading

  1. Akyildiz, H., Artis, T., Sozuer, E., Akcan, A., Kucuk, C., Sensoy, E., & Karahan, I. (2009). Internal hernia: Complex diagnostic and therapeutic problem. International Journal of Surgery7(4), 334–337. doi: 10.1016/j.ijsu.2009.04.013
  2. Lanzetta MM, Masserelli A, Addeo G, et al. Internal hernias: a difficult diagnostic challenge. Review of CT signs and clinical findings. Acta Bio-medica : Atenei Parmensis. 2019 Apr;90(5-S):20-37. DOI: 10.23750/abm.v90i5-S.8344.
  3. Koppman, J. S., Li, C., & Gandsas, A. (2008). Small Bowel Obstruction after Laparoscopic Roux-En-Y Gastric Bypass: A Review of 9,527 Patients. Journal of the American College of Surgeons206(3), 571–584. doi: 10.1016/j.jamcollsurg.2007.10.008
  4. Review of Internal Hernias: Radiographic and Clinical Findings, Lucie C. Martin, Elmar M. Merkle, and William M. Thompson, American Journal of Roentgenology 2006 186:3, 703-717
  5. Warsza, B., & Richter, B. K. (2018). Internal Hernia in Pregnant Woman after Roux-en-Y Gastric Bypass Surgery. Journal of Radiology Case Reports12(1). doi: 10.3941/jrcr.v12i1.3257
  6. Lim, R., Beekley, A., Johnson, D. C., & Davis, K. A. (2018). Early and late complications of bariatric operation. Trauma Surgery & Acute Care Open, 3(1). doi:10.1136/tsaco-2018-000219
  7. Ellsmere, J. C., Jones, D., & Chen, W. (2019, August 1). Late complications of bariatric surgical operations. Retrieved December 6, 2019, from hernias&search=internal hernia&topicRef=14953&anchor=H33&source=see_link#H33.
  8. Kurian, M., Jones, D., & Chen, W. (2019, June 4). Imaging studies after bariatric surgery. Retrieved December 6, 2019, from hernia&source=search_result&selectedTitle=4~25&usage_type=default&display_rank=4
  9. Tendler, D., & Lamont, T. (2020, February). Overview of intestinal ischemia in adults. Retrieved March 20, 2020, from necrosis§ionRank&usage_type=default&anchor=H1190364758&source=machineLearning&selectedTitle=1~150&display_rank=1#H1190364522
  10. Newsom, B. D., & Kukora, J. S. (1986). Congenital and acquired internal hernias: Unusual causes of small bowel obstruction. The American Journal of Surgery152(3), 279–285. doi: 10.1016/0002-9610(86)90258-8
  11. Lim, R., Beekley, A., Johnson, D. C., & Davis, K. A. (2018). Early and late complications of bariatric operation. Trauma Surgery & Acute Care Open, 3(1). doi:10.1136/tsaco-2018-000219

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