Internal hernia

Background

• An internal hernia is the protrusion of bowel through a peritoneal or mesenteric defect within the abdominal cavity, without involvement of the abdominal wall
• Historically, paraduodenal hernia was the most common type; however, with the rise of bariatric surgery, post-Roux-en-Y gastric bypass (RYGB) internal hernia has become the most commonly encountered form
• Reported incidence after RYGB: 2–9%, with higher rates after laparoscopic approaches (fewer adhesions → greater bowel mobility through mesenteric defects)
• This is a surgical emergency — delayed diagnosis leads to bowel ischemia, necrosis, perforation, and potentially short bowel syndrome or death

Classification

Post-bariatric (most common in current practice)

• Three potential hernia spaces are created during RYGB:
  • Petersen space: Between the Roux (alimentary) limb mesentery and the transverse mesocolon — most common in antecolic approaches
  • Jejunojejunostomy (JJ) mesenteric defect: At the enteroenterostomy between the biliopancreatic and alimentary limbs
  • Transverse mesocolon defect: Only present in retrocolic Roux limb construction; most common in retrocolic approaches
• Significant weight loss increases risk by creating laxity in the mesentery
• Average time from RYGB to internal hernia presentation: ~2–3 years, but can occur at any time

Congenital (non-surgical)

• Paraduodenal (most common congenital type; ~53% of all congenital internal hernias)
  • Left paraduodenal (fossa of Landzert) — more common
  • Right paraduodenal (fossa of Waldeyer)
• Transmesenteric
• Pericecal
• Foramen of Winslow
• Supravesical / pelvic
• Transomental

Clinical features

• Presentation ranges from intermittent, vague abdominal pain to acute surgical abdomen — highly variable and often leads to delayed diagnosis
• Symptoms may be episodic and self-resolving (spontaneous reduction of hernia) for weeks to months before an acute presentation

Classic presentation

• Postprandial, crampy, periumbilical or left upper quadrant abdominal pain
• Nausea, vomiting
• Abdominal distension
• Obstipation (if complete obstruction)
• Pain may be worsened by eating and improved by position change or lying prone

Signs of complicated internal hernia (strangulation/ischemia)

• Severe, constant abdominal pain out of proportion to exam (early ischemia)
• Peritoneal signs (rebound, guarding, rigidity)
• Hemodynamic instability (tachycardia, hypotension)
• Fever, leukocytosis
• Lactic acidosis

Biliopancreatic limb obstruction (specific to RYGB)

• May present without classic nausea/vomiting or obstipation because the obstruction is in the excluded limb
• Instead: left upper quadrant fullness, hiccoughs, unexplained tachycardia
• Left shoulder pain (from gastric remnant distension irritating the diaphragm)
• This is particularly dangerous because the closed-loop obstruction of the biliopancreatic limb can progress to remnant gastric perforation (a catastrophic event that is difficult to diagnose)

Key ED pearl

• A post-bariatric surgery patient with intermittent or acute abdominal pain should be presumed to have an internal hernia until proven otherwise
• Multiple ED visits for abdominal pain in a post-RYGB patient without a clear diagnosis is a common pattern preceding internal hernia catastrophe

Differential diagnosis

• Small bowel obstruction (adhesive)
• Incisional hernia (trocar site)
• Marginal ulcer (anastomotic ulcer)
• Anastomotic stricture
• Intussusception (at the JJ anastomosis)
• Cholelithiasis / Cholecystitis (increased risk after bariatric surgery)
• Dumping syndrome
• Pancreatitis
• Mesenteric ischemia
• Appendicitis
• Nephrolithiasis
• Gastric remnant distension/perforation (biliopancreatic limb obstruction)

Evaluation

Workup

• Determine the type of bariatric surgery performed — this is essential for interpretation of imaging and identification of potential hernia spaces
• Labs:
  • CBC (leukocytosis suggests ischemia/perforation)
  • BMP/CMP (electrolytes, renal function, bicarbonate)
  • Lactate — elevated lactate suggests bowel ischemia; however, a normal lactate does NOT exclude ischemia or strangulation
  • Lipase (exclude pancreatitis)
  • LFTs
  • Coagulation studies
  • Type and screen (anticipate possible surgical intervention)
• CT abdomen/pelvis with IV contrast — imaging modality of choice
  • Oral contrast is not required and may delay imaging
  • Obtain with multiplanar reconstructions (coronal and sagittal views are critical)

Diagnosis

• CT findings suggestive of internal hernia:
  • Mesenteric swirl sign (whirlpool sign) — twisting/swirling of the mesenteric vessels and fat; most specific finding
  • Small bowel behind the mesenteric vessels (mushroom sign)
  • Clustered small bowel loops in the left upper quadrant or in an atypical location
  • Jejunojejunostomy (JJ) anastomosis displaced to the right of midline or above the transverse colon
  • Small bowel obstruction with transition point at a mesenteric defect
  • Engorgement or stretching of mesenteric vessels
  • Hurricane eye sign — rounded configuration of distal mesenteric fat and vessels
• CT sensitivity is imperfect: Reported sensitivity ranges from 63–80%; specificity ~76%
  • Retrospective review shows diagnostic abnormalities present in up to 97% of cases, but these are frequently missed prospectively by general radiologists
  • If clinical suspicion is high and CT is equivocal or negative, surgical exploration is still indicated
• Communicate directly with the radiologist — alert them to the bariatric surgical history and ask them to specifically evaluate for internal hernia; this significantly improves diagnostic accuracy
• Upright abdominal XR: May show dilated loops or air-fluid levels but is insufficient to diagnose or exclude internal hernia; CT is mandatory
• Congenital internal hernias are typically diagnosed on CT in the setting of small bowel obstruction without prior surgical history

Management

ED management

• NPO
• IV fluid resuscitation — crystalloid bolus; correct dehydration and electrolyte abnormalities
• IV antiemetics (ondansetron)
• IV analgesia — do not withhold pain control; opioids as needed
• Nasogastric tube: Consider for decompression if significant vomiting or distension
• Broad-spectrum antibiotics: Initiate if concern for ischemia, perforation, or sepsis (e.g. piperacillin-tazobactam or cefepime + metronidazole)
• Lactate monitoring: Serial measurements; rising lactate is ominous

Surgical management

• Emergent surgical consultation for all suspected internal hernias — this is a time-sensitive surgical emergency
• Laparoscopic exploration is preferred when performed by an experienced bariatric surgeon; may require conversion to open in complicated cases
• Surgical goals:
  • Reduce herniated bowel
  • Assess bowel viability (resect necrotic segments)
  • Close mesenteric defects with non-absorbable suture to prevent recurrence
• If bowel ischemia has progressed to necrosis → segmental resection; extensive resection may result in short bowel syndrome
• Contact the patient's bariatric surgeon if possible — they know the specific anatomy and prior operative details
• If a bariatric surgeon is not available at the presenting facility, consult general surgery and arrange transfer to a bariatric center if the patient can be stabilized

Critical management pearl

• Do NOT discharge a post-bariatric surgery patient with unexplained abdominal pain and a negative or equivocal CT without surgical consultation — internal hernias can spontaneously reduce and appear normal on imaging, only to recur and strangulate

Disposition

• Operative:
  • All patients with CT findings consistent with internal hernia
  • All patients with clinical concern for ischemia or strangulation regardless of CT findings
  • Biliopancreatic limb obstruction with gastric remnant distension
• Admit with surgical consultation:
  • Equivocal CT findings in a symptomatic post-RYGB patient
  • Resolved symptoms but history concerning for intermittent internal hernia (may require elective/semi-urgent laparoscopic exploration)
• Transfer:
  • If bariatric surgical expertise is not available at the presenting facility, stabilize and transfer to a facility with bariatric surgery capability
• Discharge is rarely appropriate for post-RYGB patients with significant abdominal pain:
  • If pain fully resolves, CT is clearly negative, labs are normal, and the patient tolerates oral intake, discharge may be considered with very close follow-up (24–48 hours with bariatric surgeon)
  • Provide strict return precautions: worsening pain, vomiting, inability to eat, fever
  • Document the discussion of the risk of intermittent internal hernia and the possibility that imaging may be falsely negative

See also

• Bariatric surgery complications
• Small bowel obstruction
• Gastric bypass surgery
• Dumping syndrome
• Mesenteric ischemia
• Short bowel syndrome
• Marginal ulcer
• Incisional hernia

External links

• Prevention and management of internal hernias after bariatric surgery: an expert review - Mini-invasive Surg 2022
• Management of post-bariatric surgery emergencies - J Gastrointest Surg 2017
• Sensitivity and specificity of CT signs for internal hernia after RYGB - Clin Radiol 2009
• CT of internal hernias - Radiographics 2005
• Imaging of postoperative internal hernias - Applied Radiology