Internal Hernias: Congenital and Acquired

1. Introduction to Internal Hernias

Definition: Internal hernias involve the protrusion of the bowel or viscera through an intraabdominal aperture without passing through fascial planes. They account for 0.6% to 5.8% of small bowel obstructions.
Symptoms: Commonly presents as intermittent small bowel obstruction, with vague abdominal pain, and can be difficult to diagnose even in acute conditions.
Mortality: Mortality can be as high as 31% to 50%, particularly in acute cases.

2. Acquired Internal Hernias

Acquired Internal Hernias:
- Develop through rearrangements of intraabdominal organs, such as during liver transplantation, bowel anastomosis, or bariatric surgeries like Roux-en-Y gastric bypass (RYGB).
- Increased awareness due to rising popularity of RYGB, especially in patients with significant weight loss.
Roux-en-Y Gastric Bypass (RYGB):
- Weight Loss and Complications: Results in profound weight loss and resolution of comorbidities in 65% to 85% of cases but increases the risk of internal hernias due to the lack of adhesion formation.
- Reoperations: Internal hernias are a common reason for reoperation, typically occurring 15-33 months post-surgery.
- Defect Sites:
  - Petersen defect
  - Mesenteric defect at the jejunojejunal (JJ) anastomosis.
Presentation and Diagnosis:
- Symptoms: Obstruction, with pain, vomiting, and bowel ischemia signs like tachycardia and fever.
- Imaging: Contrast-enhanced CT is the diagnostic tool of choice. Findings include bowel clustering, aberrant vascular arrangements, and the swirl sign (indicating volvulus and ischemia).
Anatomy of the Roux-en-Y:
- Potential Herniation Sites:
  - Brolin space (mesentery defect at JJ anastomosis).
  - Petersen defect.
  - Transverse mesocolon defect (retrocolic RYGB).
- Antecolic vs. Retrocolic Approach:
  - Retrocolic approach has a higher hernia risk but routine closure reduces risk significantly.
Internal Hernia in Pregnancy:
- Increased diagnostic challenges after RYGB in pregnant women, with risks like biliary limb obstruction. Surgical exploration may be necessary, with laparoscopy safe up to 31 weeks' gestation.

3. Congenital Internal Hernias

Paraduodenal Hernia:
- Comprises 50% of all congenital internal hernias, more common in men (3:1 ratio), and typically presents in the third or fourth decade of life.
- Left Paraduodenal Hernia:
  - Bowel herniates into Landzert fossa.
  - Presentation: Postprandial abdominal pain, diagnosed around 38.5 years of age.
  - CT Findings: Clustering of small bowel in the left upper quadrant with mass effect on the stomach and transverse colon.
- Right Paraduodenal Hernia:
  - Bowel herniates into Waldeyer fossa.
  - CT Findings: Clustering of small bowel in the right upper quadrant, displacement of duodenum and colon.
Foramen of Winslow Hernia:
- Accounts for 5-10% of congenital internal hernias.
- Presentation: Symptoms of proximal small bowel obstruction, sometimes associated with jaundice.
- CT Findings: Clustering of small bowel posterior to the stomach.
Transmesenteric Hernia:
- Results from herniation through a congenital mesenteric defect, often associated with intestinal atresia in 50% of cases.
- Locations:
  - Pericecal mesentery
  - Sigmoid mesentery
  - Duodenojejunal junction
Pericecal Hernia:
- Represents 10-15% of congenital internal hernias.
- Commonly misdiagnosed as appendicitis due to clinical presentation.
- CT Findings: Clustering of small bowel lateral to the cecum.
Intersigmoid Hernia:
- Comprises 5% of congenital internal hernias.
- Results from defects in the sigmoid mesentery, allowing bowel to herniate and be trapped.
- CT Findings: Loops of small bowel in the left lower quadrant, displacing the sigmoid colon.

4. Conclusion

Internal hernias, though rare, should be considered in the differential diagnosis of small bowel obstruction, particularly in post-bariatric surgery patients. Prompt surgical response is crucial to prevent bowel ischemia and necrosis.

1. Introduction to Internal Hernias

Definition: Protrusion of bowel/viscera through an intraabdominal aperture without crossing fascial planes.
Prevalence: Accounts for 0.6% to 5.8% of small bowel obstructions.
Symptoms: Intermittent bowel obstruction, vague abdominal pain, nausea, vomiting, and distension.
Diagnosis: Often elusive; requires high suspicion. CT scan is the preferred diagnostic tool.
Mortality: Mortality can be as high as 31% to 50% in acute cases due to complications like bowel ischemia and necrosis.
Types:
- Congenital: Present from birth.
- Acquired: Result of surgery or trauma.
Management: Early diagnosis and operative intervention are key to limiting morbidity and mortality.

2. Acquired Internal Hernias

2.1 Acquired Internal Hernias

Formation: Acquired hernias develop through the creation of potential intraabdominal spaces during surgical interventions or after trauma.
Causes:
- Bowel anastomosis: Surgical joining of two bowel sections may create mesenteric defects.
- Liver transplantation: Mesocolon defects, particularly through the transverse mesocolon, are common sites.
- Roux-en-Y Gastric Bypass (RYGB): Bariatric surgery significantly increases the risk due to the creation of multiple potential spaces (e.g., Petersen’s space).
Prevalence: Increased cases with the rise in RYGB surgeries, as it predisposes patients to hernia formation due to significant weight loss and mesenteric fat reduction.

2.2 Roux-en-Y Gastric Bypass (RYGB)

Purpose: A bariatric surgery designed for weight reduction, achieving 65-85% excess weight loss and resolving multiple comorbidities like diabetes, sleep apnea, hypertension, GERD, and depression.
Complications: Post-RYGB patients are prone to developing internal hernias, especially after laparoscopic procedures, which result in less adhesion formation, leading to more mobile bowel segments.
Herniation Sites:
- Petersen’s defect: A mesenteric gap between the Roux limb and transverse mesocolon.
- Mesenteric defect at the jejunojejunal (JJ) anastomosis: The most common site, created during surgery to join the Roux limb and biliopancreatic limb.
Incidence:
- Internal hernias occur in 1.8% to 7.6% of post-RYGB patients.
- Reoperation rates for internal hernias are between 6.9% and 13%, with the highest reoperation rates occurring within the first two years after surgery.

2.3 Presentation and Diagnosis

Symptoms:
- Roux limb obstruction: Epigastric or left upper quadrant pain, often relieved by vomiting. May present with signs of high-grade obstruction (50% of cases).
- Common channel obstruction: Similar to Roux limb obstruction but accompanied by bilious emesis, indicating obstruction beyond the JJ anastomosis.
- Biliopancreatic limb herniation: Rare, presenting with remnant gastric distension, tachycardia, and hiccups.
Physical Exam: Nonspecific, but signs of bowel ischemia (e.g., tachycardia, fever, localized tenderness) should raise suspicion of an internal hernia.
Laboratory Findings: Nondiagnostic but may include leukocytosis and amylasemia.
Imaging:
- CT Scan is the diagnostic tool of choice. Key signs include:
  - Swirl sign: Twisting of the mesenteric vessels, indicative of volvulus and potential bowel ischemia.
  - Bowel clustering: Bowel loops appearing in abnormal positions, often displaced due to the hernia.
  - Mesenteric vessel abnormalities: Engorgement or abrupt changes in vessel direction.

2.4 Anatomy of the Roux-en-Y

Roux-en-Y Structure:
- Roux limb: Typically 100-150 cm, connected to a small 15-mL gastric pouch.
- Retrocolic vs. Antecolic Approach:
  - Retrocolic: Higher incidence of hernias due to increased potential for mesocolic defects.
  - Antecolic: Lower risk but still prone to Petersen's hernia.
Common Defect Sites:
- Brolin space: Mesentery defect at the jejunojejunal (JJ) anastomosis.
- Petersen defect: Mesentery defect between the Roux limb and transverse mesocolon.
- Transverse mesocolon defect: Seen more often with the retrocolic approach.

Hernia Prevention:
- Mesenteric defect closure with nonabsorbable sutures can significantly reduce hernia risk. Studies show a hernia incidence of 0.2% to 0.7% with proper closure of the defects.

2.5 Internal Hernia in Pregnancy

Diagnostic Challenges: Pregnant women with a history of RYGB who present with abdominal pain pose a unique diagnostic challenge due to anatomical changes and the risk of internal hernias.
- Comorbidities: Patients may have additional complications such as gallbladder disease or biliary limb obstruction, which must be ruled out with ultrasound.
Management:
- Imaging: Ultrasound should be the first imaging tool to rule out gallbladder pathology. CT may be avoided due to fetal radiation risks.
- Surgical Exploration: Should be considered early due to the low negative predictive value of CT and the potential for bowel ischemia. Laparoscopy is safe up to 31 weeks of gestation; beyond this, open surgery or a combined cesarean section with exploration may be needed after 36 weeks.

3. Congenital Internal Hernias

Congenital internal hernias are present from birth and result from defects in the normal development of the mesentery or peritoneum during fetal development. These hernias are rare, often diagnosed later in life, and can cause bowel obstruction with a high risk of ischemia and necrosis due to delayed diagnosis.

3.1 Paraduodenal Hernia

Prevalence: Accounts for 50% of all congenital internal hernias.
Gender Prevalence: More common in men (3:1 ratio).
Age of Presentation: Typically presents in the third or fourth decade of life.
Types:
1. Left Paraduodenal Hernia:
  - Pathogenesis: Results from herniation into the Landzert fossa (a potential space near the left colonic mesentery).
  - CT Findings: Clustering of small bowel in the left upper quadrant with mass effect on the posterior stomach and transverse colon. May show anterior displacement of the inferior mesenteric vein (IMV) and ascending left colic artery.
  - Symptoms: Intermittent postprandial abdominal pain, often self-resolving. Diagnosis often delayed, with an average age of 38.5 years.
  - Treatment: Surgical reduction of the hernia, with repair of the defect using nonabsorbable sutures. In cases of difficult reduction, ligation of the IMV and ascending colic artery may be necessary.
2. Right Paraduodenal Hernia:
  - Pathogenesis: Herniation into the Waldeyer fossa, located behind the right colon mesentery.
  - CT Findings: Clustering of small bowel in the right upper quadrant, with displacement of the duodenum and colon. May show malrotation of the small bowel and incomplete rotation of the ligament of Treitz.
  - Treatment: Surgical reduction of the hernia, with care taken to avoid damage to the superior mesenteric artery (SMA). In severe cases, a procedure similar to the Ladd procedure may be performed, leaving the bowel in a non-rotated state and removing the appendix to prevent future complications.

3.2 Foramen of Winslow Hernia

Prevalence: Comprises 5-10% of congenital internal hernias. Approximately 160 adult cases and 4 pediatric cases have been described.
Anatomy: The foramen of Winslow is a natural aperture between the caudate lobe, inferior vena cava, duodenum, and hepatoduodenal ligament (which contains the portal triad).
Associated Conditions: Often associated with malrotation of the intestines.
Presentation: Patients present with proximal small bowel obstruction symptoms. There may be gastric outlet obstruction or jaundice if the common bile duct is involved. Necrotic bowel may not lead to peritonitis since the bowel is isolated in the lesser sac.
CT Findings: Small bowel loops clustered posterior to the stomach with anterior displacement of the stomach. May resemble a left paraduodenal hernia, but the bowel is higher in the right upper quadrant.
Treatment: Reduction of herniated contents into the peritoneal cavity. Widening the foramen is not typically feasible due to surrounding vital structures. If a malrotated cecum is involved, cecectomy may be necessary.

3.3 Transmesenteric Hernia

Definition: Herniation through a defect in the mesentery, which can be either congenital or acquired.
Pathogenesis: Likely caused by a failure of proper mesenteric development during fetal growth, often linked to in utero ischemic events similar to those that cause intestinal atresia.
Associated Anomalies: Intestinal atresia is found in about 50% of infants presenting with transmesenteric hernias.
Common Locations:
- Pericecal mesentery
- Sigmoid mesentery
- Duodenojejunal junction
Presentation: These hernias may remain asymptomatic for years or cause chronic abdominal pain and bowel obstruction.

3.4 Pericecal Hernia

Prevalence: Comprises 10-15% of congenital internal hernias.
Pathogenesis: Results from the failure of proper development of the pericecal mesentery, likely due to an ischemic event during fetal life. This creates an aperture through which the bowel may herniate.
Clinical Presentation: Often mistaken for appendicitis due to the location of pain and tenderness.
CT Findings: Clustering of small bowel loops lateral to the cecum, with anterior displacement of the cecum.
Treatment: Surgical reduction of the herniated bowel, closure of the aperture, and resection of necrotic bowel if necessary.

3.5 Intersigmoid Hernia

Prevalence: Represents 5% of congenital internal hernias.
Pathogenesis: Caused by improper development or redundancy in the sigmoid mesentery, forming a sac or pseudo sac where the bowel can herniate and become trapped.
CT Findings: Loops of small bowel displaced in the left lower quadrant, often pushing the sigmoid colon anteriorly or medially.
Treatment: Surgical reduction of the hernia and closure of any mesenteric defects. If necrotic bowel is present, resection may be necessary.

This detailed summary expands on each type of congenital internal hernia, providing a clear overview of their pathogenesis, clinical presentation, diagnostic findings, and treatment options. Let me know if you'd like to proceed with further sections or focus on specific areas for revision!