What is the recommended diagnostic and management approach for a patient with an adrenal mass that has inconclusive imaging?

Management of Inconclusive Adrenal Mass Imaging

For an adrenal mass with inconclusive imaging after initial evaluation, proceed with second-line imaging using either chemical shift MRI or washout CT, followed by comprehensive hormonal screening, and then use shared decision-making to choose between repeat imaging in 3-6 months versus surgical resection based on size, growth characteristics, and malignancy risk stratification.

Algorithmic Approach to Inconclusive Adrenal Masses

Step 1: Confirm Non-Contrast CT Has Been Performed

If not already done, obtain non-contrast CT (NCCT) as the essential first-line study 1. This establishes the critical Hounsfield Unit (HU) measurement that drives all subsequent decisions.

Step 2: Risk Stratification Based on HU and Size

The 2023 CUA/AUA and 2025 ESE guidelines provide clear thresholds 2, 1:

• HU ≤10: Benign adenoma (0% malignancy risk) - no further imaging needed
• HU 11-20 and <4 cm: Indeterminate (0.5% malignancy risk) - requires second-line imaging
• HU >20 or ≥4 cm with heterogeneity: Suspicious (6.3% malignancy risk) - multidisciplinary discussion for surgery consideration

Step 3: Second-Line Imaging for Indeterminate Masses

For masses with HU 11-20 or other indeterminate features, obtain either:

1. Chemical shift MRI (increasingly preferred 2)

   • Detects microscopic fat indicating lipid-rich adenoma
   • Homogeneous signal intensity drop = benign adenoma
   • Heterogeneous drop is controversial (can occur in pheochromocytoma, ACC, some metastases)

2. Washout CT (with important caveats 1)

   • Critical limitation: ~33% of pheochromocytomas washout like adenomas
   • Critical limitation: ~33% of adenomas don't washout in adenoma range
   • Malignant masses can also show adenoma-range washout
   • Use with caution and awareness of these false positive/negative rates

3. FDG-PET/CT (for suspected malignancy 2)

   • Sensitivity 93-100% for malignancy
   • Maximum standardized uptake value ratio >1.8 (adrenal mass to liver) suggests malignancy
   • Particularly useful when metastatic disease is a consideration

Step 4: Mandatory Hormonal Screening

All patients require comprehensive hormonal evaluation regardless of imaging findings 1:

1. Autonomous cortisol secretion (all patients):

   • 1 mg dexamethasone suppression test
   • Cortisol >50 nmol/L (>1.8 µg/dL) = mild autonomous cortisol secretion (MACS)

2. Pheochromocytoma screening:

   • Required if HU >10 OR any signs/symptoms of catecholamine excess
   • Plasma-free metanephrines or 24-hour urinary metanephrines
   • Must exclude before any biopsy to prevent hypertensive crisis

3. Primary aldosteronism (if hypertension/hypokalemia):

   • Aldosterone-to-renin ratio

4. Androgen excess (if virilization or suspected ACC):

   • Serum androgen testing

Step 5: Management Decision Algorithm

After second-line imaging and hormonal workup, the mass falls into one of these categories:

A. Still Indeterminate, Non-Functional, <4 cm

Shared decision-making between two options 1:

• Option 1: Repeat imaging in 3-6 months
• Option 2: Surgical resection

Factors favoring surgery:

• Patient anxiety about malignancy
• Younger age (adrenal masses rarer and more concerning in young adults)
• Any growth on prior imaging
• Patient preference to avoid surveillance

Factors favoring surveillance:

• Higher surgical risk
• Patient preference
• Stable size on any prior imaging

B. Indeterminate, Non-Functional, ≥4 cm

• Repeat imaging in 6-12 months 1
• Growth >5 mm/year: Repeat hormonal workup and consider surgery 1
• Growth <3 mm/year: No further follow-up needed 1

C. Suspicious Features (HU >20, Heterogeneous, ≥4 cm)

• Multidisciplinary conference required 2
• Consider surgical resection vs. follow-up in 6-12 months if surgery declined
• If suspected ACC: surgery is indicated (minimally invasive if <6 cm and capsule intact; open if larger or locally advanced) 1

D. Functional Mass (Any Hormone Excess)

• Pheochromocytoma or aldosterone-secreting adenoma: Surgery indicated 1
• MACS with progressive metabolic comorbidities: Consider surgery in younger patients 1
• Overt Cushing's syndrome: Surgery indicated 1

Step 6: Role of Biopsy

Biopsy is NOT routinely indicated 1. Consider only when:

• Diagnosis of metastatic disease from extra-adrenal malignancy would change management
• Never biopsy suspected ACC (risk of tumor seeding)
• Always exclude pheochromocytoma first (prevent hypertensive crisis)

Critical Pitfalls to Avoid

1. Washout CT limitations: Don't assume a mass is benign based solely on washout characteristics - one-third of pheochromocytomas and some ACCs can mimic adenomas 1

2. Missing hormonal screening: Imaging alone is insufficient - lipid-poor adenomas overlap with malignant masses and pheochromocytomas 1

3. Size threshold misinterpretation: The 4 cm threshold is for follow-up decisions, not absolute surgical indication 1

4. Bilateral lesions: Evaluate each lesion individually using the same criteria 2

5. Young patients: Lower threshold for aggressive workup - adrenal masses are rarer and more likely malignant in young adults, children, and pregnant patients 1

Special Populations

Patients with known extra-adrenal malignancy: FDG-PET can help differentiate benign adenoma from metastasis (uptake ratio >1.8 suggests metastasis) 2, 3

Elderly patients: Balance surgical risk against malignancy risk and life expectancy in decision-making

Pregnancy: Prefer chemical shift MRI over CT for radiation safety 1