What is the recommended hormonal work‑up and imaging follow‑up for a patient with an adrenal incidentaloma smaller than 4 cm?

Work-up for Adrenal Incidentaloma <4 cm

All patients with adrenal incidentalomas <4 cm require comprehensive hormonal screening regardless of imaging characteristics, but if the lesion is benign-appearing (homogeneous with ≤10 HU on non-contrast CT) and non-functional, no further imaging follow-up is needed. 1

Hormonal Work-up (Required for ALL Patients)

Mandatory Screening Tests

Screen every patient for the following, regardless of symptoms:

• Autonomous cortisol secretion: 1 mg overnight dexamethasone suppression test (DST)

  • Abnormal if serum cortisol >50 nmol/L (>1.8 µg/dL) post-suppression 1
  • This is the single most important test as mild autonomous cortisol secretion (MACS) occurs in 5-30% of incidentalomas and increases cardiovascular mortality 2

• Pheochromocytoma screening:

  • Skip this test ONLY if the lesion is unequivocally benign (≤10 HU on non-contrast CT) AND the patient has zero signs/symptoms of catecholamine excess 1
  • For all other cases: plasma-free metanephrines or 24-hour urinary metanephrines 1
  • Critical caveat: Approximately 1/3 of pheochromocytomas can mimic benign adenomas on washout CT, so don't rely solely on imaging 1

• Primary aldosteronism: Aldosterone-to-renin ratio (ARR)

  • Only required if patient has hypertension and/or hypokalemia 1
  • Abnormal if ARR >30 3

• Androgen excess: Serum DHEA-S, testosterone, androstenedione

  • Only if suspected adrenocortical carcinoma OR clinical virilization signs present 1

Imaging Follow-up Algorithm

For Lesions <4 cm:

The imaging follow-up depends entirely on radiological characteristics and functionality:

Scenario 1: Benign-appearing AND non-functional

• Homogeneous lesion with ≤10 HU on non-contrast CT + negative hormonal work-up
• Action: NO further imaging or hormonal testing required 1, 2
• This applies to myelolipomas and other masses with macroscopic fat as well 1

Scenario 2: Indeterminate imaging (11-20 HU) AND non-functional

• Immediate additional imaging with either:
  • Adrenal protocol CT with washout, OR
  • Chemical shift MRI, OR
  • PET-CT 4
• Alternative approach: Follow-up imaging at 12 months instead of immediate additional imaging 4
• If additional imaging confirms benign features: no further follow-up needed
• If remains indeterminate: repeat imaging at 6-12 months 4

Scenario 3: Suspicious features (>20 HU or heterogeneous)

• Multidisciplinary discussion required 4
• Consider surgical resection vs. follow-up imaging at 6-12 months 4

Scenario 4: Any functional lesion

• Proceed to surgery regardless of size or imaging characteristics 1
• Exception: MACS without progressive metabolic comorbidities can be observed with annual clinical screening 1

Growth Rate Thresholds (if surveillance chosen):

• >5 mm/year growth: Consider adrenalectomy after repeating functional work-up 1
• <3 mm/year growth: No further imaging or functional testing needed 1
• Growth of >0.8 cm over 3-12 months predicts malignancy 5, 3

Critical Pitfalls to Avoid

1. Don't skip cortisol screening: Even "benign-looking" lesions can be functional, and MACS is associated with increased mortality 2

2. Don't rely on washout CT alone: 1/3 of pheochromocytomas wash out like adenomas, and 1/3 of adenomas don't wash out appropriately 1

3. Never biopsy before excluding pheochromocytoma: This can precipitate hypertensive crisis 1

4. Don't assume bilateral lesions are the same: Each lesion requires separate characterization 1

5. Age matters: Adrenal lesions in young adults, children, and pregnant patients have higher malignancy risk and warrant expedited evaluation 1

Special Populations

Patients with known extra-adrenal malignancy: These are NOT true incidentalomas—approximately 50% may represent metastases, requiring different evaluation 6

Bilateral incidentalomas: Additionally measure 17-hydroxyprogesterone (exclude congenital adrenal hyperplasia) and assess for adrenal insufficiency 1