What is the optimal method to localize a Conn's (aldosterone‑producing) adenoma?

Localizing Conn's Adenoma

Adrenal venous sampling (AVS) is the gold standard for localizing aldosterone-producing adenomas and should be performed in all surgical candidates to distinguish unilateral adenoma from bilateral hyperplasia, as CT imaging alone leads to unnecessary adrenalectomy in approximately 25% of cases. 1

Diagnostic Algorithm for Localization

Step 1: Initial Imaging with CT or MRI

• Perform CT or MRI of the adrenal glands as the initial anatomic localization study 1
• Critical limitation: CT has only 82% sensitivity for detecting aldosteronomas, missing tumors smaller than 1 cm 2
• CT alone is unreliable because non-functioning adenomas and nodular hyperplasia are common, leading to false-positive results 1
• If CT shows a unilateral mass >1 cm with no contralateral abnormality in patients <40 years old, some institutions may proceed directly to surgery, though this remains controversial 1

Step 2: Adrenal Venous Sampling (Mandatory for Surgical Candidates)

• AVS is considered the standard for distinguishing unilateral adenomas from bilateral hyperplasia 1
• Perform simultaneous bilateral AVS with ACTH stimulation for optimal accuracy 3
• Measure both aldosterone and cortisol in catheterization samples to confirm proper catheter placement 1, 4
• Key diagnostic thresholds:
  • Aldosterone-to-cortisol ratio (higher side/lower side) >2.6 after ACTH stimulation indicates unilateral disease with 98% sensitivity and 100% specificity 3
  • Absolute aldosterone concentration >1,340 ng/dL on the affected side has 92% sensitivity and 100% specificity 3

Step 3: Pre-AVS Preparation

• Discontinue mineralocorticoid receptor antagonists (spironolactone/eplerenone) at least 4 weeks before AVS to avoid pharmacologic interference 4
• Normalize serum potassium levels prior to the procedure 4
• Ensure unrestricted dietary salt intake before testing 4

Treatment Based on Localization Results

Unilateral Aldosterone Production (Adenoma)

• Laparoscopic adrenalectomy is the treatment of choice 1
• Improves blood pressure in virtually 100% of patients and cures hypertension in approximately 50% 4, 5
• Surgical series report no deaths, minimal morbidity, and mean postoperative stay of 2.6 days 1

Bilateral Aldosterone Production (Hyperplasia)

• Medical management with spironolactone or eplerenone for lifelong control of hypertension and hypokalemia 1
• Eplerenone 50-100 mg daily is preferred when patients experience anti-androgenic side effects like gynecomastia from spironolactone 4

Critical Pitfalls to Avoid

• Never rely on CT imaging alone for surgical decision-making: Reports indicate 25% of patients would undergo unnecessary adrenalectomy based on CT findings without AVS confirmation 1, 4
• Do not assume hypokalemia is required for diagnosis: Up to 50% of patients with aldosteronoma are normokalemic, especially in early stages 5, 6
• Recognize that adenomas on imaging may be non-functioning: Nodular hyperplasia of the zona glomerulosa occurs even with functioning adenomas elsewhere 1
• AVS alters clinical management in 35.7% of patients who would have been treated improperly based on imaging alone 4

Special Considerations

• In patients <40 years old with clear unilateral adenoma on CT and no contralateral abnormality, some NCCN institutions suggest it may be reasonable to exclude AVS, though this remains institution-dependent 1
• Exclude glucocorticoid-remediable aldosteronism through genetic testing before proceeding with invasive localization studies 7, 6
• The aldosterone-to-renin ratio >30 should be confirmed with aldosterone suppression testing before proceeding to localization studies 5, 7