What are the radiographic criteria for an adrenal mass?

From the Guidelines

Adrenal masses are considered benign if they have a density of less than 10 Hounsfield Units (HU) on non-contrast CT.

Radiographic Criteria

The following are the radiographic criteria for an adrenal mass:

• Non-contrast CT: A density of less than 10 HU is suggestive of a benign lesion 1.
• Washout CT: A washout of more than 60% in 15 minutes is suggestive of a benign lesion 1.
• Chemical-shift MRI: Signal drop out is suggestive of a benign lesion 1.
• Size: Lesions larger than 4 cm should undergo repeat imaging in 6-12 months, while lesions larger than 5 cm have a higher risk of malignancy and should be removed 1.

Imaging Modalities

The following imaging modalities can be used to evaluate an adrenal mass:

• CT: Non-contrast and contrast-enhanced CT can be used to evaluate the density and washout characteristics of the lesion 1.
• MRI: Chemical-shift MRI can be used to evaluate the signal characteristics of the lesion 1.
• PET/CT: Can be used to evaluate the metabolic activity of the lesion, with low uptake suggestive of a benign lesion 1.

Clinical Context

It is essential to consider the clinical context when evaluating an adrenal mass, including the patient's history, physical examination, and laboratory results 1. In patients with a history of malignancy, even smaller adrenal lesions are suspect, and a more thorough evaluation is necessary 1. In patients with signs or symptoms of adrenal hormone excess, further evaluation with laboratory tests and imaging is necessary 1.

From the Research

Radiographic Criteria for Adrenal Masses

The radiographic criteria for adrenal masses can be assessed using various imaging modalities, including computed tomography (CT), magnetic resonance (MR) imaging, and fluorine-18 fluorodeoxyglucose PET combined with CT 2, 3, 4. The criteria for characterizing an adrenal mass as benign or malignant include:

• Unenhanced CT attenuation of less than or equal to 10 Hounsfield Units (HU) for lipid-rich adrenal adenomas 4
• Absolute enhancement washout of ≥ 60% and/or relative enhancement washout of ≥ 40% on adrenal washout contrast-enhanced CT for adrenal adenomas 4
• Signal loss in opposed-phased MR imaging for adrenal adenomas 4
• Size and heterogeneity of the mass, with larger and more heterogeneous masses being more suspicious for malignancy 5

Imaging Modalities

Different imaging modalities have different strengths and weaknesses in evaluating adrenal masses:

• Unenhanced CT is useful for characterizing lipid-rich adrenal adenomas 4
• Contrast-enhanced CT is useful for characterizing adrenal adenomas based on their washout characteristics 4
• MR imaging is useful for characterizing adrenal adenomas based on their signal loss in opposed-phased imaging 4
• Fluorodeoxyglucose-positron emission tomography (FDG-PET) can be helpful in characterizing some lesions, particularly in differentiating benign from malignant lesions 3, 4

Specific Pathologies

Certain adrenal pathologies have specific imaging characteristics:

• Adrenal adenomas are typically homogeneous and have low attenuation on unenhanced CT 4
• Adrenal cysts and myelolipomas have characteristic fluid and fat content, respectively 5
• Pheochromocytomas are rare neuroendocrine tumors of the adrenal medulla and may have characteristic imaging appearances 5
• Metastases to the adrenal glands are the most common malignant adrenal tumors and may have variable imaging appearances 5