What is the recommended follow-up interval for MRI in an elderly male with a small 1 cm left adrenal adenoma?

Follow-up Imaging for 1 cm Adrenal Adenoma in Elderly Male

No further follow-up imaging or functional testing is required for this patient. 1, 2

Rationale for No Follow-up

The most recent high-quality guidelines from the Canadian Urological Association and American Urological Association (2023) provide a strong recommendation that patients with benign non-functional adenomas less than 4 cm do not require further follow-up imaging or functional testing once initial characterization is complete. 1, 2

This recommendation is based on:

• Size criterion: At 1 cm, this mass is well below the 4 cm threshold that triggers continued surveillance. 1
• Malignancy risk: Benign-appearing masses <4 cm have essentially 0% risk of malignant transformation. 2
• Evidence quality: This is a strong recommendation with moderate quality evidence from the highest-tier guideline bodies. 1

Critical Prerequisites That Must Be Confirmed

Before discontinuing follow-up, you must verify the following were completed during initial workup:

Radiological Confirmation of Benignity

• Hounsfield units ≤10 on unenhanced CT, which confirms a lipid-rich adenoma. 1, 2
• If HU was >10 initially, washout CT or chemical shift MRI should have been performed to confirm benign characteristics. 1

Complete Hormonal Screening

All patients require initial hormonal evaluation regardless of imaging appearance: 1, 2

• 1 mg overnight dexamethasone suppression test (cortisol ≤50 nmol/L or ≤1.8 µg/dL excludes autonomous cortisol secretion) 1, 3
• Plasma-free and/or urinary fractionated metanephrines to exclude pheochromocytoma 1
• Aldosterone-to-renin ratio if hypertension or hypokalemia present 1

Approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment, making this initial hormonal evaluation non-negotiable. 2

Divergent Guideline Perspectives

While the 2023 CUA/AUA guidelines provide the most definitive recommendation for no follow-up, older guidelines suggest variable approaches: 1

• European Society of Endocrinology (ESE) and American College of Radiology (ACR): Also recommend no follow-up imaging for benign-appearing masses. 1
• AACE/AAES: Recommend reimaging in 3-6 months, then annually for 1-2 years. 1
• Korean Endocrine Society (KES): Recommend repeat CT at 12 months if mass <2 cm with no change. 1

The 2023 CUA/AUA guideline supersedes these older recommendations and represents the current standard of care based on accumulated evidence showing no benefit to continued imaging of small, benign-appearing masses. 1, 2

Important Exceptions That Would Change Management

If Mass is ≥4 cm

Even radiologically benign masses ≥4 cm require repeat imaging in 6-12 months due to higher baseline malignancy risk. 1, 2

If Hormonal Symptoms Develop

Consider annual symptom screening, as 17% of initially non-functional masses develop hormone secretion after 1 year, increasing to 47% by 5 years. 2, 4

If Initial Imaging Was Indeterminate

Masses with HU >10 without adequate washout characterization require either: 1

• Repeat imaging in 3-6 months, or
• Shared decision-making regarding surgical resection

Common Pitfalls to Avoid

• Do not perform routine adrenal biopsy: This is contraindicated for adrenal incidentalomas unless there is known extra-adrenal malignancy and confirmation of metastatic disease would alter management. 2
• Do not continue imaging for benign-appearing masses <4 cm: The evidence shows these masses have essentially 0% risk of malignant transformation. 2
• Do not skip initial hormonal evaluation: Even for radiologically benign lesions, subclinical hormone excess occurs in 5% of incidentalomas. 2
• Elderly age alone does not mandate follow-up: While adrenal incidentalomas are more common in elderly patients (10% prevalence over age 70), benign small masses still do not require surveillance. 1