What is the process of adrenal vein sampling?

Adrenal Vein Sampling: Process and Protocol

Adrenal vein sampling (AVS) is the gold standard procedure for distinguishing between unilateral and bilateral aldosterone production in patients with primary aldosteronism, as it is more reliable than CT imaging alone for determining the source of excessive aldosterone production. 1

Purpose and Indications

• Primary indication: Determine if aldosterone production is unilateral (adenoma) or bilateral (hyperplasia) in confirmed primary aldosteronism
• Critical for treatment decision-making:
  • Unilateral disease → surgical adrenalectomy (potential cure)
  • Bilateral disease → medical management with mineralocorticoid receptor antagonists

Pre-Procedure Considerations

• Must rule out pheochromocytoma before performing AVS to prevent catecholamine crisis 1
• Some institutions may exclude AVS in patients younger than 40 years when imaging shows only one affected gland, as bilateral hyperplasia is rare in this population 2
• Patient should be a surgical candidate for the procedure to be worthwhile

Technical Procedure

1. Patient Preparation:

   • Withdraw mineralocorticoid receptor antagonists for ≥4 weeks before testing
   • Ensure normal serum potassium and unrestricted salt intake

2. Catheterization Process:

   • Performed by an interventional radiologist under fluoroscopic guidance
   • Sequential or simultaneous catheterization of both adrenal veins
   • Right adrenal vein is technically more challenging to cannulate due to its small size and direct drainage into the inferior vena cava 3
   • Left adrenal vein is typically easier to access as it drains into the left renal vein

3. Sampling Protocol:

   • Blood samples collected from both adrenal veins and a peripheral vein (usually inferior vena cava)
   • Samples analyzed for both aldosterone and cortisol concentrations
   • Some protocols include ACTH stimulation to maximize cortisol gradients and improve diagnostic accuracy 4

4. Confirmation of Successful Cannulation:

   • Measured by the adrenal vein to peripheral vein cortisol ratio
   • Higher quality criteria require a ratio ≥2.75 for reliable results 5
   • Technical success rates as high as 97% in experienced hands 3

Interpretation of Results

1. Cannulation Success Assessment:

   • Adrenal/peripheral vein cortisol ratio confirms proper catheter placement
   • Three levels of criteria exist 5:
     • Permissive (type 1): Lower threshold but poor reproducibility
     • Intermediate (type 2): Moderate threshold
     • Strict (type 3): Higher threshold with better reproducibility

2. Lateralization Assessment:

   • Calculated using the aldosterone-to-cortisol ratio from each adrenal vein
   • Dominant side shows significantly higher aldosterone production
   • Cortisol measurement corrects for dilution effects and confirms proper catheter placement 2

Clinical Impact

• AVS changes management in approximately 39% of patients compared to imaging alone 6
• Prevents unnecessary surgery in patients with bilateral disease misdiagnosed by imaging
• Identifies surgical candidates with unilateral disease who might otherwise receive lifelong medical therapy
• Essential for accurate subtyping of primary aldosteronism

Potential Complications

• Adrenal vein rupture (main concern but rare with experienced operators) 7
• Groin hematoma at access site
• Contrast reaction
• Radiation exposure

Pitfalls and Considerations

• Poor reproducibility with permissive criteria for successful cannulation 5
• Variability in protocols between institutions affects interpretation 4
• Technical difficulty in cannulating the right adrenal vein may lead to sampling failure
• Experience of the interventional radiologist significantly impacts success rates

AVS remains underutilized despite its importance in directing appropriate treatment for primary aldosteronism. When performed correctly with appropriate criteria for cannulation and lateralization, it provides crucial information that significantly impacts patient management and outcomes.