What is the treatment for an adrenal incidentaloma with 38% absolute washout?

Management of Adrenal Incidentaloma with 38% Absolute Washout

This adrenal incidentaloma with 38% absolute washout is indeterminate and requires shared decision-making between repeat imaging in 3-6 months versus surgical resection, after completing a full hormonal workup to exclude functional tumors. 1

Understanding the Washout Result

An absolute washout of 38% falls below the traditional 60% threshold used to characterize benign adenomas, placing this lesion in the indeterminate category. 1 However, recent evidence highlights critical limitations of washout CT:

• Approximately one-third of benign adenomas fail to washout in the typical adenoma range (≥60%), meaning your lesion could still be benign despite the low washout. 1
• Conversely, some malignant masses (including adrenocortical carcinoma and hypervascular metastases) can demonstrate washout values in the adenoma range, creating false reassurance. 1
• About one-third of pheochromocytomas also washout like adenomas, making functional testing mandatory regardless of imaging. 1

Critical First Step: Complete Hormonal Evaluation

Before any imaging or surgical decisions, you must exclude functional tumors to prevent life-threatening complications and identify lesions requiring surgery regardless of imaging characteristics. 1

Required Hormonal Tests:

• 1 mg overnight dexamethasone suppression test to screen for autonomous cortisol secretion (cortisol >50 nmol/L or >1.8 µg/dL is abnormal). 1, 2
• Plasma or 24-hour urinary metanephrines to exclude pheochromocytoma (essential before any biopsy or surgery). 1, 3
• Aldosterone-to-renin ratio only if you have hypertension and/or hypokalemia. 1

Size-Dependent Management Algorithm

The management pathway depends critically on the lesion size, which you did not specify:

If Lesion is <4 cm:

• Repeat imaging in 3-6 months is the preferred conservative approach for indeterminate non-functional masses. [1, @15@]
• If growth is >5 mm/year, repeat the functional workup and consider adrenalectomy. 1
• If growth is <3 mm/year, no further follow-up is needed. 1

If Lesion is 4-6 cm:

• Repeat imaging in 3-6 months initially. 1
• If enlarging >1 cm in 1 year, proceed to adrenalectomy for suspected carcinoma. 1
• Shared decision-making is essential given intermediate malignancy risk. 1

If Lesion is >6 cm:

• Surgical resection should be strongly considered given higher malignancy risk, regardless of washout characteristics. 1
• Obtain chest, abdomen, and pelvis imaging to evaluate for metastases before surgery. 1

Additional Imaging Considerations

If you want to avoid repeat CT and further characterize the lesion now, chemical shift MRI is an alternative second-line imaging option that may provide additional diagnostic information without radiation exposure. 1 Homogeneous signal intensity drop on MRI indicates lipid-rich adenoma, though heterogeneous signal drop is less specific. 1

Surgical Decision-Making

Adrenalectomy is definitively indicated if: 1

• Pheochromocytoma is confirmed (minimally invasive surgery preferred)
• Aldosterone-secreting adenoma with confirmed unilateral production on adrenal vein sampling
• Clinically apparent Cushing's syndrome from unilateral cortisol-secreting mass
• Growth >5 mm/year on surveillance imaging after repeat functional workup

Minimally invasive surgery should be performed when feasible for functional tumors and suspected adrenocortical carcinomas that can be safely resected without capsule rupture. 1

Critical Pitfalls to Avoid

• Never perform adrenal biopsy for routine workup of incidentalomas—it is rarely indicated and carries risks including tumor seeding and hemorrhage. 1
• Never proceed with any intervention before excluding pheochromocytoma, as undiagnosed pheochromocytoma can cause life-threatening hypertensive crisis during surgery or biopsy. 1, 4
• Do not rely solely on washout values to exclude malignancy or pheochromocytoma given the significant false positive and false negative rates. 1
• Do not assume non-functional status based on imaging alone—approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment. 3, 4

If Hormonal Testing is Normal

For a non-functional indeterminate lesion, the 2023 CUA/AUA guidelines explicitly recommend shared decision-making with management options of repeat imaging in 3-6 months versus surgical resection. [1, @15@] The choice depends on patient age, comorbidities, anxiety level, surgical risk, and lesion size. Younger, healthier patients with larger lesions may reasonably choose upfront surgery, while older patients with smaller lesions typically favor surveillance.