What is the recommended radiological imaging for Median Arcuate Ligament Syndrome (MALS)?

Radiological Imaging for Median Arcuate Ligament Syndrome (MALS)

CT angiography (CTA) of the abdomen and pelvis is the recommended first-line imaging modality for diagnosing Median Arcuate Ligament Syndrome (MALS), followed by mesenteric angiography in lateral projection during both inspiration and expiration to confirm the diagnosis if needed. 1

Initial Diagnostic Imaging

CT Angiography (CTA)

• CTA provides the highest accuracy and inter-reader agreement for grading mesenteric vessel stenosis with sensitivity and specificity of 95-100% 2
• Key findings on CTA include:
  • Characteristic "J-shaped" or "hooked" appearance of the proximal celiac artery 1, 3
  • Focal narrowing in the proximal celiac axis 3
  • Upward deflection of the celiac artery (fold angle <135° suggests MALS) 4
  • Post-stenotic dilation of the celiac artery 5
• CTA should be performed during both inspiratory and expiratory phases to demonstrate dynamic compression 1

Confirmatory Imaging

If CTA findings suggest MALS, the following may be used for confirmation:

1. Mesenteric Angiography:

   • Performed in lateral projection during both inspiration and expiration 2
   • Rated 7/9 (usually appropriate) by the American College of Radiology 2
   • Documents dynamic worsening of stenosis during expiration 1
   • Identifies mesenteric collateralization, which helps predict surgical outcomes 2
   • Patients with collateralization on angiography are less likely to benefit from surgical release 2

2. Duplex Doppler Ultrasound:

   • Useful as a screening tool and for follow-up 2
   • Best performed in fasting state to avoid bowel gas 2
   • Peak systolic velocity cutoffs for stenosis:
     • SMA: 295 cm/s for 50% stenosis, 400 cm/s for 70% stenosis
     • Celiac artery: 240 cm/s for 70% stenosis 2
   • Can demonstrate respiratory variation in celiac artery flow 6

Diagnostic Criteria

• Stenosis >30% is considered the threshold for intervention 1
• Fold angle (FA) measurement is important:
  • FA <135° (hook sign) is significantly associated with symptomatic MALS 4
  • Patients with MALS have more severe FA (120.7° ± 33.6°) compared to those without MALS (134.8° ± 27.9°) 4

Post-Treatment Imaging

• Duplex ultrasound or CTA at 6 months and annually thereafter to assess:
  • Patency of vascular reconstruction
  • Resolution of stenosis
  • Development of potential complications like aneurysms 1, 7

Clinical Pitfalls and Considerations

1. Incidental findings vs. symptomatic disease:

   • Celiac axis compression occurs in 10-24% of asymptomatic individuals 5
   • Correlation with clinical symptoms is essential for diagnosis 5

2. Differential diagnosis:

   • Atherosclerotic disease can mimic MALS but typically lacks the characteristic "hook" appearance 3
   • Calcified atherosclerotic plaque is common in elderly and cannot be relied upon for MALS diagnosis 2

3. Potential complications requiring imaging surveillance:

   • Development of collateral circulation (present in 69.6% of MALS patients) 7
   • Visceral artery aneurysms (occur in 47.8% of MALS patients) 7
   • Aneurysm rupture (36.4% of those with aneurysms) 7

4. Body habitus considerations:

   • Fold angle is negatively correlated with BMI in patients with celiac artery compression 4
   • In patients with BMI >25, those with MALS have narrower FA (112.6° ± 30.5°) compared to those without MALS (131.7° ± 30.3°) 4

By following this imaging algorithm, clinicians can accurately diagnose MALS, guide appropriate treatment decisions, and monitor for potential complications that may significantly impact patient morbidity and mortality.