What is the best scan to detect adrenal gland tumors?

Best Imaging for Adrenal Gland Tumors

Non-contrast CT of the abdomen is the best initial scan to detect and characterize adrenal gland tumors, with lesions measuring <10 Hounsfield Units (HU) being diagnostic of benign adenomas. 1, 2

Initial Imaging Approach

• Non-contrast CT is the first-line test with an appropriateness rating of 8/9 by the American College of Radiology for evaluating adrenal masses 1, 2
• Lesions measuring <10 HU on non-contrast CT are benign adenomas with high specificity, requiring no further workup 1, 2
• This threshold exploits the lipid content of adenomas, which lowers their attenuation coefficient 2
• Non-contrast CT is relatively inexpensive, widely available, and highly specific for differentiating benign from malignant lesions 1

Second-Line Imaging for Indeterminate Lesions (>10 HU)

When non-contrast CT shows density >10 HU or the mass is discovered on contrast-enhanced CT, you have two equally appropriate options (both rated 8/9):

Option 1: CT with Delayed Enhancement (Washout Protocol)

• Perform contrast-enhanced CT followed by 15-minute delayed imaging 1
• Adenomas demonstrate >60% absolute washout, achieving sensitivity >95% and specificity >97% 1, 2
• Critical pitfall: Approximately 1/3 of pheochromocytomas may show adenoma-like washout patterns, and 1/3 of adenomas may not washout in the typical range 2

Option 2: Chemical Shift MRI

• Equally appropriate (rated 8/9) for indeterminate lesions 1, 2
• Detects microscopic fat in adenomas through signal intensity drop on out-of-phase imaging 1, 2
• Superior to CT for lesions with density 10-30 HU, correctly characterizing 89% of adenomas in this indeterminate range 1
• Particularly useful when lesion is identified only on contrast-enhanced CT 1

Clinical Context Matters

Patients WITHOUT History of Malignancy

• For masses <3 cm: Non-contrast CT or chemical shift MRI (both rated 8/9) 1
• For masses 3-5 cm: Same imaging approach, but also consider follow-up CT/MRI at 3-6 months (rated 8/9) 1
• Masses >5 cm should be surgically removed 1

Patients WITH History of Malignancy

• Non-contrast CT remains first-line (rated 8/9) 1
• Adrenal biopsy becomes more appropriate (rated 8/9 vs. 4/9 in patients without cancer history) 1
• FDG-PET has moderate utility (rated 6/9) for lung, colon, lymphoma, and melanoma metastases 1
• FDG-PET pitfall: False-negatives occur with renal cell carcinoma metastases 1

Imaging Modalities to Avoid

• Ultrasound: Rated 2/9 - inadequate for characterization 1
• Plain X-ray: Rated 2/9 - no role in adrenal tumor evaluation 1
• MIBG scan: Rated 2/9 - only for suspected pheochromocytoma 1
• Dynamic enhanced MRI: Rated 2-4/9 - mixed results in literature, not fully validated 1

Critical Safety Consideration

Always exclude pheochromocytoma biochemically before any biopsy - several deaths have been reported from biopsying undiagnosed pheochromocytomas 1, 2, 3

Follow-Up Strategy

• For indeterminate benign-appearing lesions: Repeat imaging at 3-6 months (rated 8/9) 1, 2
• For lesions ≥4 cm that are radiologically benign (<10 HU): Repeat imaging at 6-12 months 2
• No further follow-up needed if growth is <3 mm/year 2