Management of 1.5 cm Adrenal Adenoma
A 1.5 cm adrenal adenoma that is non-functioning and radiologically benign (≤10 Hounsfield units on unenhanced CT) requires no further follow-up imaging or functional testing. 1, 2
Initial Hormonal Evaluation Required
Even though this mass is small and likely benign, all patients with adrenal incidentalomas require initial hormonal screening regardless of size or benign appearance on imaging, as approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment. 2, 3
The mandatory hormonal workup includes:
- 1 mg overnight dexamethasone suppression test to screen for autonomous cortisol secretion (mild autonomous cortisol secretion/MACS) 2, 3
- Plasma or 24-hour urinary metanephrines to exclude pheochromocytoma 2, 3
- Aldosterone-to-renin ratio only if the patient has hypertension and/or hypokalemia 2, 3
Critical pitfall to avoid: Skipping hormonal evaluation can lead to undiagnosed pheochromocytoma, which can cause life-threatening hypertensive crisis during any future surgical procedure. 3
Imaging Characterization
Unenhanced CT should be obtained to measure Hounsfield units (HU). 2
- If HU ≤10: The mass is definitively a benign lipid-rich adenoma and requires no further imaging 2, 3
- If HU >10: Second-line imaging with either washout CT or chemical shift MRI should be performed 1, 2
Important caveat: Approximately 1/3 of pheochromocytomas may washout in the characteristic range of an adenoma, and roughly 1/3 of adrenal adenomas do not washout in the adenoma range, so clinicians must be aware of these limitations when interpreting washout CT. 1
Management Algorithm Based on Results
If Non-Functional and Benign (HU ≤10):
No further follow-up imaging or functional testing is required, based on moderate-quality evidence showing a 0% to <1% risk of malignant transformation. 1, 2 This is a strong recommendation from the American Urological Association/Canadian Urological Association 2023 guidelines. 1
If Functional Abnormalities Detected:
- Pheochromocytoma or aldosterone-secreting adenoma: Adrenalectomy is indicated, preferably via minimally invasive surgery when feasible 1, 2
- Mild autonomous cortisol secretion (MACS): Adrenalectomy should be considered only in younger patients with progressive metabolic comorbidities attributable to cortisol excess after shared decision-making 1, 2
- Patients not managed surgically with MACS: Annual clinical screening for new or worsening associated comorbidities 1
Size-Specific Considerations
At 1.5 cm, this mass falls well below the 4 cm threshold that typically triggers surveillance imaging. 1, 2 Lesions <4 cm that are benign and non-functional require no further surveillance. 1, 2
The risk for primary adrenal cortical carcinoma in the general population is only 0.06%, and most small (<3 cm) incidentally discovered adrenal masses in patients without a history of malignancy are benign. 2
Special Population Exception
If the patient has a history of extra-adrenal malignancy, the approach differs significantly, with a higher suspicion for metastatic disease (25-72% depending on the primary tumor type). 2 In this scenario, biopsy may be considered after excluding pheochromocytoma. 1
Common Pitfalls to Avoid
- Never perform adrenal mass biopsy routinely for the workup of an adrenal incidentaloma, as this is rarely indicated and carries unnecessary risks including potential tumor seeding 1, 2, 3
- Do not order unnecessary repeated imaging for small adrenal masses with benign characteristics, as this leads to increased radiation exposure, patient anxiety, and healthcare costs 2
- Do not skip initial hormonal evaluation even if the mass appears benign on imaging, as functional abnormalities occur in approximately 5% of cases and require treatment 2, 3