When is imaging recommended for evaluation of an adrenal mass or lesion?

When is Imaging Recommended for Adrenal Masses?

All adrenal lesions >1 cm require dedicated imaging with non-contrast CT (NCCT) as the first-line study unless the lesion is clearly benign on initial imaging, and lesions <1 cm require imaging only if there is clinical concern for hormone excess. 1

Initial Imaging Approach

Size-Based Threshold

• Lesions >1 cm: Require further dedicated imaging unless clearly identified as benign
• Lesions <1 cm: Imaging only needed if clinical concern for hormone excess exists 1

First-Line Imaging: Non-Contrast CT (NCCT)

NCCT should be the initial imaging study unless previously performed. This allows measurement of attenuation in Hounsfield Units (HU), which is critical for characterization 1.

Risk-Stratified Imaging Pathways

Based on the 2023 European Society of Endocrinologists guidelines, imaging recommendations follow four distinct pathways 1:

1. Homogeneous Lesions ≤10 HU on NCCT

• No further imaging required - these are benign adenomas
• Specificity of 98% for benign diagnosis 1

2. Lesions 11-20 HU, <4 cm

• Immediate additional imaging with adrenal protocol CT, MRI with chemical shift imaging (CSI), or PET-CT
• Alternative: Follow-up imaging at 12 months instead of immediate additional imaging
• If additional imaging confirms benign features, no further follow-up needed
• If indeterminate after additional imaging, requires follow-up 1

3. High-Risk Lesions (Relevant Malignancy Risk)

Require multidisciplinary conference discussion with consideration of surgical resection or 6-12 month follow-up:

• Heterogeneous lesions ≥4 cm (regardless of HU)
• Any lesion with NCCT attenuation >20 HU (regardless of size) 1

4. Indeterminate Lesions

Lesions not meeting above criteria require individualized management:

• <4 cm AND (heterogeneous OR >20 HU)

• 4 cm with attenuation 11-20 HU

• Consider prompt further imaging or surgical resection
• Follow-up imaging necessary if not resected and remains indeterminate 1

Special Populations Requiring Urgent Imaging

Patients <40 Years or Pregnant Patients

• Urgent assessment with MRI preferred over CT (to avoid radiation)
• Higher risk of malignancy or clinically relevant hormone excess
• Surgical resection should be considered for lesions not characteristically benign
• Even benign-appearing lesions may warrant single follow-up at 12 months 1

Patients with Extra-Adrenal Malignancy

• Higher likelihood of metastasis, but still evaluate for benign features first
• 74% of lesions in patients with past malignancy are benign
• 53% benign in concurrent malignancy without metastases
• 25% benign even with signs of metastatic disease 2
• Dedicated adrenal imaging remains essential to avoid unnecessary treatment

Follow-Up Imaging Protocols

For Indeterminate Lesions Under Surveillance

• NCCT or MRI at 6-12 months initially 1
• Lesions stable for at least 12 months can usually be considered benign without ongoing imaging
• Critical caveat: Hormone excess must still be excluded, as some lesions (e.g., pheochromocytomas) may remain stable in size 1

Growth Thresholds Suggesting Malignancy

• Consider surgical resection if lesion enlarges ≥5 mm AND increases maximum diameter by >20% 1
• Growth of ≥8 mm in 12 months warrants further investigation
• Lesions not meeting these cutoffs may have repeat imaging in 6-12 months 1

Second-Line Imaging Modalities

When NCCT is indeterminate (>10 HU), options include:

Adrenal Protocol CT

• Three phases: non-contrast, venous (60-70 seconds), delayed (15 minutes)
• Calculates contrast washout characteristics
• Growing concern about washout calculation performance in incidentaloma setting 1

MRI with Chemical Shift Imaging

• Increasingly favored over adrenal protocol CT 1
• Superior for lesions with CT density 10-30 HU (89% correctly characterized) 3
• Can correctly characterize up to 60% of lesions misclassified by CT 3

PET-CT

• FDG-PET for suspected malignancy (sensitivity 93-100%) 1
• Maximum standardized uptake value ratio >1.8 (adrenal mass to liver) suggests malignancy 1
• DOTATATE with Gallium-68 superior to FDG for suspected pheochromocytoma/paraganglioma 1

Common Pitfalls to Avoid

1. Don't skip imaging for lesions >1 cm even if asymptomatic - 30% of "non-functioning" adenomas actually have hormone excess 1

2. Don't assume malignancy in cancer patients - even with metastatic disease, 25% of adrenal lesions are benign 2

3. Don't rely solely on size - 91% of adrenocortical carcinomas were <4 cm in one large review, though risk increases significantly with size 1

4. Don't stop at imaging - comprehensive biochemical evaluation is mandatory for all adrenal lesions to exclude hormone excess (MACS, pheochromocytoma, primary aldosteronism) 1

5. Bilateral lesions: Evaluate each lesion's imaging characteristics individually 1