What is the diagnostic approach for Median Arcuate Ligament Syndrome (MALS)?

Diagnostic Approach for Median Arcuate Ligament Syndrome (MALS)

The diagnosis of MALS requires a combination of clinical presentation, characteristic imaging findings on CT angiography showing "J-shaped" narrowing of the proximal celiac artery, and lateral projection mesenteric angiography during both inspiration and expiration to document dynamic worsening of stenosis. 1

Clinical Presentation

• Typical symptoms:

  • Postprandial abdominal pain
  • Nausea and vomiting
  • Weight loss (significant predictor of successful surgical outcome when >20 pounds)
  • Food aversion
  • Exercise-induced abdominal pain 1, 2

• Physical examination:

  • May reveal an abdominal bruit
  • Laboratory findings may include anemia, leucopenia, electrolyte abnormalities, and hypoalbuminemia (secondary to malnutrition) 1

Diagnostic Imaging Algorithm

1. CT Angiography (CTA) - First-Line Imaging

• Sensitivity and specificity of 95-100% for grading mesenteric vessel stenosis
• Should include both arterial and venous phases with 1mm slices
• Characteristic findings: proximal narrowing of the celiac artery in a "J-shaped" configuration
• Also evaluates for other potential causes of abdominal pain 1, 3

2. Duplex Doppler Ultrasound

• Useful as a screening tool and for follow-up
• Should be performed in the fasting state to avoid bowel gas
• Diagnostic criteria for celiac artery stenosis: peak systolic velocity >240 cm/s for 70% stenosis
• Can demonstrate respiratory variation in celiac artery flow velocities 1

3. Mesenteric Angiography

• Confirmation test for MALS
• Should be performed in lateral projection during both inspiration and expiration
• Documents dynamic worsening of stenosis during expiration
• Evaluates mesenteric collateralization (important prognostic factor)
• Patients with collateralization on angiography are less likely to benefit from surgical release 3, 1

Diagnostic Pitfalls and Considerations

1. Prevalence of asymptomatic compression: Celiac axis narrowing due to median arcuate ligament occurs in approximately 20% of the general population, often asymptomatic due to collateral circulation 3, 1

2. Diagnosis of exclusion: MALS must be considered after ruling out other gastrointestinal pathologies that can cause similar symptoms 2, 4

3. Multifactorial etiology: Beyond vascular compression, MALS has neurogenic components involving the celiac plexus that contribute to symptomatology 1, 2

4. Predictors of successful surgical outcome:

   • Postprandial pain pattern
   • Age between 40-60 years
   • Weight loss >20 pounds 1

5. Delayed diagnosis: Consideration of MALS in patients' diagnostic workup is typically delayed due to vague symptoms and lack of awareness 2

Diagnostic Confirmation

The definitive diagnosis of MALS requires correlation between:

• Characteristic clinical symptoms
• Imaging findings demonstrating celiac artery compression
• Exclusion of other causes of abdominal pain
• In some cases, response to treatment may be confirmatory 1, 2

MALS remains a challenging diagnosis due to its rarity and the overlap of symptoms with other more common gastrointestinal conditions. A high index of suspicion is required, particularly in younger to middle-aged patients with postprandial pain and weight loss who have negative workups for other conditions.