CT Protocol for Adrenal Incidentaloma Evaluation

Initial Imaging Approach

Non-contrast CT is the recommended first-line imaging modality for adrenal incidentaloma characterization, with homogeneous, well-circumscribed lesions <10 Hounsfield Units (HU) considered benign 1
The American College of Radiology assigns an appropriateness rating of 8/9 (highly appropriate) for both non-contrast CT and delayed enhancement CT in the evaluation of adrenal incidentalomas 3

Delayed enhancement CT evaluates the washout characteristics of adrenal masses after contrast administration, with adenomas typically demonstrating rapid washout of contrast (>60% absolute washout or >40% relative washout at 15 minutes) 3, 4
Chemical shift MRI exploits the different frequency of protons in water and fat to detect microscopic fat, with homogeneous signal intensity drop on MRI diagnostic of lipid-rich adenoma 1
The American College of Radiology assigns an appropriateness rating of 8/9 for chemical shift MRI in adrenal incidentaloma evaluation 3

Approximately 1/3 of pheochromocytomas may demonstrate washout in the characteristic range of an adenoma, potentially leading to false negatives 1
Malignant masses can sometimes washout in the adenoma range, resulting in adrenal cortical carcinoma or hypervascular metastases being mistaken for adenomas 1

If <10 HU and homogeneous on non-contrast CT: Benign adenoma, no further imaging needed 1
If rapid washout on CT or signal drop on MRI: Likely benign adenoma 3, 1

All patients with adrenal incidentalomas should undergo hormonal evaluation regardless of imaging characteristics, as imaging cannot reliably predict functionality 1
Biochemical testing (plasma or 24-hour urinary metanephrines) must be performed before any invasive procedure, including biopsy, to exclude pheochromocytoma and avoid hypertensive crisis 1