What is the size threshold for surgical removal of adrenal adenomas?

Size Threshold for Surgical Removal of Adrenal Adenomas

For non-functional adrenal adenomas that are radiologically benign (≤10 HU on unenhanced CT), surgery should be considered when the lesion is ≥4 cm, though this is not an absolute indication and requires repeat imaging at 6-12 months before making a definitive surgical decision. 1

Primary Size-Based Algorithm

Lesions <4 cm

• No surgery is required for benign non-functional adenomas <4 cm with radiologically benign features (≤10 HU on unenhanced CT), and no further follow-up imaging or functional testing is necessary 1, 2, 3
• This represents a strong recommendation with moderate quality evidence from the most recent 2023 CUA/AUA guidelines 1
• The malignancy risk in this size range is extremely low when imaging characteristics are benign 4

Lesions ≥4 cm

• Repeat imaging in 6-12 months is recommended even for radiologically benign lesions (≤10 HU), as most surgically resected pheochromocytomas and adrenocortical carcinomas were >4 cm at diagnosis 1, 2, 3
• This is a weak recommendation with low-quality evidence, reflecting that the 4 cm threshold is based on retrospective data rather than prospective trials 1
• Surgery should be considered if the lesion grows >5 mm/year on follow-up imaging after repeating functional workup 1, 2, 3
• Lesions growing <3 mm/year require no further imaging or functional testing 1, 2

Lesions >6 cm

• The European Society of Endocrinology suggests 6 cm as a cutoff for considering open rather than laparoscopic adrenalectomy for suspected adrenocortical carcinoma, though this is not based on high-quality evidence 1
• Research data shows that 46.7% of malignant tumors were 3-4 cm in size, while 29.1% of benign lesions were 5-6 cm, indicating size criteria alone have limited value 5

Critical Nuances and Exceptions

Imaging Characteristics Trump Size

• The 4 cm threshold only applies to radiologically benign lesions (≤10 HU on unenhanced CT or demonstrating >60% absolute washout on enhanced CT) 1
• If HU >10 on unenhanced CT, enhanced CT with washout protocol or chemical shift MRI is mandatory regardless of size 1, 2
• Lesions with irregular margins, internal heterogeneity, or HU >10 should be strongly suspected of malignancy even if <4 cm 1

Functional Status Overrides Size Criteria

• All hormone-secreting adenomas require surgical removal regardless of size, including aldosterone-secreting adenomas and pheochromocytomas 1
• Approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment, making initial hormonal evaluation mandatory for all adrenal incidentalomas regardless of size or imaging appearance 2, 3

Special Populations Requiring Lower Thresholds

• Young adults, children, and pregnant patients require expedited evaluation and lower thresholds for surgery, as adrenal lesions are more likely malignant in these populations 1, 3
• Patients with a history of extra-adrenal malignancy have a 25-72% risk of adrenal metastases depending on primary tumor type, and the 4 cm threshold does not apply 3

Common Pitfalls to Avoid

• Never skip initial hormonal evaluation even for small, radiologically benign lesions, as subclinical hormone excess occurs in 5% of incidentalomas and requires treatment regardless of size 2, 3
• Do not assume bilateral lesions represent metastatic disease—bilateral adenomas are common, especially in older patients, and each lesion should be separately characterized 2, 6
• Avoid routine adrenal biopsy, which should be reserved only for cases where noninvasive techniques are equivocal with high suspicion for metastatic disease in patients with known extra-adrenal malignancy 2, 3
• Do not rely solely on size criteria for determining malignancy risk, as research shows significant overlap between benign and malignant lesions across all size ranges 5, 7

Surgical Approach Considerations

• Minimally invasive surgery (laparoscopic or retroperitoneoscopic) should be performed when feasible for benign lesions and suspected pheochromocytomas 1
• For suspected adrenocortical carcinoma, open adrenalectomy is preferred due to increased risk of local recurrence and peritoneal spread with laparoscopic approaches 1
• Experienced surgeons can safely perform laparoscopic adrenalectomy for lesions >6 cm, though conversion rates, operating time, and blood loss are increased 8, 9