At what size are adrenal nodules considered to not require further workup?

Adrenal Nodules Not Requiring Further Workup

Adrenal nodules less than 40 mm (4 cm) that are benign-appearing on imaging and non-functional do not require further follow-up imaging or functional testing. 1

Size Thresholds for No Further Workup

The critical size cutoff is <40 mm (<4 cm) for adrenal incidentalomas that meet specific criteria 1:

• Benign non-functional adenomas <40 mm require no further follow-up imaging or functional testing (strong recommendation, moderate quality evidence) 1

• Myelolipomas and other small masses containing macroscopic fat detected on initial workup do not require further follow-up regardless of exact size if clearly identified 1

• Lesions <30 mm (<3 cm) have an extremely low malignancy risk (0.3%) in patients without known cancer history 2, 3

Required Imaging Characteristics for Observation

Before concluding no workup is needed, the nodule must demonstrate benign imaging features 4, 5:

• Hounsfield units (HU) ≤10 on unenhanced CT - these are definitively benign adenomas and require no additional imaging independent of size 5

• Homogeneous appearance with well-defined margins 4, 5

• If HU >10, second-line imaging with washout CT or chemical shift MRI must confirm benign characteristics before observation 1, 5

Critical Exception: Functional Assessment Still Required

All adrenal incidentalomas, regardless of size or benign appearance, require initial hormonal evaluation 4, 6:

• 1 mg overnight dexamethasone suppression test (cortisol should be ≤50 nmol/L or ≤1.8 µg/dL) 5

• Plasma or urinary metanephrines to exclude pheochromocytoma 5

• Plasma aldosterone and renin ratio if hypertensive or hypokalemic 4

This is a common pitfall - approximately 5% of radiologically benign incidentalomas have subclinical hormone production that requires treatment 1, 4

Size-Based Management Algorithm

For nodules ≥40 mm (≥4 cm):

• Even if radiologically benign (HU <10), repeat imaging in 6-12 months is recommended 1
• This threshold exists because most surgically resected pheochromocytomas and adrenocortical carcinomas were >40 mm at diagnosis 1

For nodules 30-50 mm (3-5 cm):

• Require second-line imaging (washout CT or chemical shift MRI) if not already performed 6
• Malignancy risk increases in this size range 1, 6

For nodules >50 mm (>5 cm):

• Surgical resection should be strongly considered due to significantly elevated malignancy risk (21.1% for nodules ≥40 mm) 1, 2

Special Population Considerations

Patients with history of extra-adrenal malignancy:

• Even small adrenal lesions warrant closer evaluation as metastatic risk is 25-72% depending on primary tumor 1, 4
• The 40 mm threshold does not apply in this population 1

Young adults, children, and pregnant patients:

• Adrenal lesions are more likely malignant and evaluation should be expedited 1
• Consider low-dose CT or chemical shift MRI for radiation safety 1

Growth Rate Thresholds

If follow-up imaging is performed for any reason 1:

• Growth <3 mm/year: No further imaging or functional testing required 1

• Growth >5 mm/year: Consider adrenalectomy after repeating functional workup 1

Common Pitfalls to Avoid

• Failing to perform initial hormonal evaluation on radiologically benign lesions - subclinical hormone excess occurs in 5% of incidentalomas and requires treatment 1, 4

• Ordering washout CT for lesions with HU ≤10 - this is unnecessary as these are definitively benign 5

• Unnecessary repeated imaging for small (<40 mm) benign-appearing non-functional adenomas leads to increased radiation exposure, patient anxiety, and healthcare costs 7

• Performing adrenal biopsy routinely - this should be reserved only for cases where noninvasive techniques are equivocal with high suspicion for metastatic disease 1, 4