What is Petersen's mesenteric defect?

Petersen's Mesenteric Defect

Definition and Anatomic Location

Petersen's space (or Petersen's defect) is a mesenteric gap located between the Roux alimentary limb, the transverse mesocolon, and the retroperitoneum that forms after gastrojejunostomy procedures, most commonly Roux-en-Y gastric bypass (RYGB). 1

This anatomic space represents one of three potential sites for internal hernia formation after RYGB surgery, alongside the transverse mesocolon defect (in retrocolic bypasses) and the jejuno-jejunostomy mesenteric defect. 1

Clinical Significance

Incidence and Risk Factors

• Internal hernia through Petersen's space accounts for approximately 54% of small bowel obstructions after RYGB, making it the most common cause of post-bariatric obstruction. 2

• The laparoscopic approach to RYGB paradoxically increases the risk of Petersen's hernia compared to open surgery, because the absence of postoperative adhesions permits greater bowel mobility and facilitates herniation through the defect. 3

• Greater weight loss after bariatric surgery appears to increase the risk of developing internal hernias, likely due to reduction in mesenteric fat that previously filled the potential space. 4

Clinical Presentation

• Patients typically present with intermittent crampy epigastric pain that may radiate to the back, often accompanied by nausea and vomiting. 5, 3, 6

• Symptoms may be nonspecific and intermittent, making diagnosis challenging; a high index of suspicion is required in any post-RYGB patient with abdominal pain. 3, 6

• The mean time to presentation is approximately 13.5 to 24 months after the initial bypass surgery, though hernias can occur as early as 3 weeks or as late as several years postoperatively. 6, 7

Diagnostic Approach

Imaging Findings

• Contrast-enhanced CT is the diagnostic modality of choice, though its sensitivity for detecting internal hernias is only 14.8–51.9%, while specificity exceeds 90%. 5

• Key radiologic signs include:

  • "Swirl sign" (clustered bowel loops with mesenteric vessels swirling around a central point) 2
  • Mushroom-shaped mesentery configuration 6
  • Abnormal bowel clustering or displacement 2
  • Mesenteric edema and engorgement 5

• CT predicts the diagnosis in only 73% of cases, meaning a negative CT does not exclude internal hernia when clinical suspicion is high. 7

When to Pursue Surgical Exploration

• Exploratory laparoscopy should be performed within 12–24 hours in stable post-RYGB patients with persistent abdominal pain and inconclusive imaging, because delayed diagnosis markedly increases the risk of bowel ischemia and resection. 1, 2

• The threshold for diagnostic laparoscopy must be deliberately low given the poor sensitivity of imaging and the catastrophic consequences of missed strangulation. 2, 7

Surgical Management

Intraoperative Approach

• Surgical exploration after RYGB should follow a systematic sequence: 1

  1. Begin at the ileocecal junction (distal to obstruction)
  2. Follow the alimentary limb proximally to the jejuno-jejunostomy
  3. Inspect all three potential hernia sites: Petersen's space, transverse mesocolon defect, and jejuno-jejunostomy mesenteric defect
  4. Examine the remnant stomach

• When an internal hernia is identified, assess bowel viability immediately; if ischemia is present, resection is mandatory. 1

Defect Closure

• All mesenteric defects should be closed with non-absorbable suture material (running or interrupted technique) to prevent recurrence. 1

• Closure of both the jejunal mesenteric defect and Petersen's space reduces the internal hernia rate from approximately 3.34% to 0.91% compared to closure of the jejunal defect alone. 7

• Routine closure of Petersen's defect during primary RYGB surgery is strongly recommended, as it halves the incidence of subsequent internal hernias (from 2.58% to 1.15% in matched cohorts). 7

• Non-closure strategies result in a 6.5% rate of manifest internal hernias, with Petersen's space being the most common site (5.3% at the jejunal mesenteric space alone). 4

Critical Pitfalls

• Do not delay surgical exploration beyond 12–24 hours when internal hernia is suspected, even if imaging is negative or equivocal; persistent postoperative pain alone justifies operative evaluation. 2, 5

• Do not rely solely on CT findings to exclude internal hernia; clinical judgment must prevail when symptoms are consistent with obstruction. 5, 7

• Do not assume that passage of flatus or stool excludes a Petersen's hernia, as partial obstruction may be intermittent. 5