What is the recommended follow-up approach for a lipid-rich adrenal adenoma?

Follow-Up for Lipid-Rich Adrenal Adenoma

Patients with lipid-rich adrenal adenomas (<10 HU on unenhanced CT) that are <4 cm require no further imaging follow-up or functional testing. 1

Initial Confirmation of Lipid-Rich Adenoma

A lipid-rich adenoma is definitively diagnosed when the mass demonstrates ≤10 Hounsfield units (HU) on unenhanced CT, which carries a 0% risk of adrenocortical carcinoma. 1 This imaging characteristic confirms the benign nature of the lesion with high specificity. 2, 3

Size-Based Follow-Up Algorithm

Small Lipid-Rich Adenomas (<4 cm)

• No further imaging or functional testing is required for benign non-functional adenomas <4 cm with confirmed lipid-rich characteristics (HU <10). 1
• Prospective data demonstrates that these lesions show minimal growth (mean 1±2 mm over 5 years) and do not develop hormonal hypersecretion. 4
• Screening for pheochromocytoma is not needed in patients with unequivocal adrenocortical adenomas confirmed on unenhanced CT (HU <10) and no signs or symptoms of adrenergic excess. 1

Large Lipid-Rich Adenomas (≥4 cm)

• Repeat imaging should be performed in 6-12 months for non-functional adrenal lesions that are radiologically benign (<10 HU) but ≥4 cm. 1
• This exception exists because most surgically resected pheochromocytomas and adrenocortical carcinomas were >4 cm at diagnosis, though data supporting this threshold are limited. 1

One-Time Hormonal Evaluation Required

Despite the benign imaging appearance, all patients with adrenal incidentalomas must undergo initial hormonal screening before discontinuing follow-up: 1, 5

• 1 mg overnight dexamethasone suppression test to screen for autonomous cortisol secretion (cortisol should be ≤1.8 μg/dL or ≤50 nmol/L). 5
• Plasma or 24-hour urinary metanephrines only if HU >10 or if patient has signs/symptoms of catecholamine excess. 1, 5
• Aldosterone-to-renin ratio only if the patient has hypertension and/or hypokalemia. 1, 5

This one-time evaluation is critical because approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment. 6

Growth Threshold for Intervention

If follow-up imaging is performed for any reason:

• Adrenalectomy should be considered for lesions growing >5 mm/year after repeating functional work-up. 1
• No further imaging is required for lesions growing <3 mm/year. 1
• The largest tumor growth observed in a 5-year prospective study of lipid-rich adenomas was 8 mm, which proved to be a benign cortical adenoma on histopathology. 4

Critical Pitfalls to Avoid

• Do not perform adrenal biopsy for adrenal incidentalomas, as it is rarely indicated and carries unnecessary risks including potential tumor seeding. 1, 6
• Do not skip the initial hormonal evaluation even for clearly benign-appearing lesions, as undiagnosed pheochromocytoma can cause life-threatening hypertensive crisis during any surgical procedure. 6
• Be aware that 97% of lipid-rich adenomas maintain their low attenuation (<10 HU) on follow-up imaging, confirming their stability. 4