Imaging and Management of Incidentally Discovered Adrenal Masses

Initial Evaluation

• The American College of Radiology recommends obtaining a dedicated non-contrast CT of the abdomen to measure the adrenal mass density in Hounsfield Units (HU) as the essential first step to determine if the lesion is a benign lipid-rich adenoma or requires further characterization 1, 2
• The American College of Radiology assigns non-contrast CT the highest appropriateness rating (8 out of 9) for evaluating incidentally discovered adrenal masses 1, 2

Imaging Algorithm

• If the mass measures <10 HU and appears homogeneous and well-circumscribed, it is definitively a benign lipid-rich adenoma requiring no further imaging workup 3
• If the mass measures >10 HU, proceed immediately to second-line imaging with either delayed contrast-enhanced CT (washout protocol) or chemical shift MRI to further characterize the lesion 1, 2

Patient Selection

• For patients without known malignancy, most small adrenal masses (<3 cm) are benign, and the non-contrast CT approach is appropriate 1, 2
• For patients with known or suspected lung cancer, the same non-contrast CT is still the first step (appropriateness rating 8/9) 2
• For patients with known or suspected lung cancer, FDG-PET has higher utility (appropriateness rating 6/9) specifically for lung cancer, colon cancer, lymphoma, and neuroendocrine tumors, as metastases typically show uptake values >4 1, 2

Size-Based Considerations

• Adrenal masses <3 cm are usually benign, and extensive workup is usually not justified in patients without cancer history 1, 2
• Adrenal masses 3-5 cm require second-line imaging (washout CT or chemical shift MRI) regardless of HU measurement 1, 4
• Adrenal masses ≥4 cm require repeat imaging in 6-12 months, even if radiologically benign (<10 HU) 5, 4
• Adrenal masses >5 cm should be removed due to higher malignancy risk 1, 2, 4

Critical Pitfall to Avoid

• Do not proceed directly to adrenal biopsy, as it is rarely indicated and carries unnecessary risks, including tumor seeding and potential hypertensive crisis if an undiagnosed pheochromocytoma is present 3, 6

Concurrent Hormonal Evaluation

• Simultaneously initiate hormonal workup regardless of imaging characteristics, as approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment 3, 6

Management of Adrenal Masses with Uncertain Malignancy

Diagnostic Approach

• When MRI suggests an adrenal abscess but cannot definitively exclude malignancy, proceed with immediate hormonal evaluation, obtain dedicated non-contrast CT to measure Hounsfield units, and pursue multidisciplinary discussion regarding either CT-guided aspiration/drainage with culture or surgical resection, as recommended by the American Urological Association 7
• If imaging remains indeterminate after CT, repeat imaging in 3-6 months is reasonable for masses <4 cm with equivocal features, according to the American College of Radiology 7
• PET-CT can be useful in patients with history of malignancy, particularly lung cancer, colon cancer, lymphoma, or neuroendocrine tumors, where metastases typically show SUV >4, as suggested by the Society of Nuclear Medicine and Molecular Imaging 7
• Chemical shift MRI is an alternative second-line test, particularly for younger patients or when radiation exposure is a concern, as recommended by the American College of Radiology 7

Management Decisions

• Do not routinely biopsy suspected primary adrenal malignancy due to risk of tumor seeding and dissemination, as advised by the American Urological Association 7
• Biopsy should only be considered when suspicion of primary adrenal malignancy is remote and pathology would directly influence management, such as suspected metastatic disease from known extra-adrenal primary, according to the National Comprehensive Cancer Network 7
• Surgical resection is indicated when mass is >4 cm with inhomogeneous appearance or HU >20, or when mass shows growth >5 mm/year on follow-up imaging, as recommended by the American Urological Association 7

Workup and Management of Incidentally Detected Adrenal Adenoma

Radiological Assessment

• A dedicated non‑contrast CT should be obtained to measure lesion attenuation in Hounsfield Units (HU) when not already performed. – American College of Radiology (ACR) recommendation. 8
• If the lesion measures ≤10 HU, it is classified as a benign lipid‑rich adenoma on imaging alone. – ACR evidence. [8][9]
• If the lesion measures >10 HU, second‑line imaging with either delayed contrast‑enhanced CT (washout protocol at 10–15 min) or chemical‑shift MRI is required. – ACR guidance. [8][9]
• A washout >50 % on delayed CT (10–15 min) confirms a benign adenoma. – ACR diagnostic criterion. 8
• Signal intensity loss on opposed‑phase chemical‑shift MRI confirms adenoma. – ACR imaging criterion. 9
• Lesions <3 cm are almost universally benign in patients without a known cancer history. – ACR risk stratification data. 8
• Lesions ≥4 cm carry a higher risk of malignancy and warrant follow‑up imaging even when radiologically benign. – Urology guideline (The Journal of Urology). 10

Hormonal Evaluation

• All patients with an adrenal adenoma on CT require hormonal evaluation because 5–12 % have subclinical hormone production that mandates treatment. – Urology guideline. 10
• Screen for autonomous cortisol secretion with a 1 mg overnight dexamethasone suppression test; a cortisol level >5 µg/dL indicates subclinical Cushing syndrome, present in 5–12 % of incidentalomas. – ACR and Urology guideline. [8][10]
• Measure the aldosterone‑to‑renin ratio only in patients with hypertension or unexplained hypokalemia to screen for primary aldosteronism. – Urology guideline. 10
• If imaging suggests adrenal cortical carcinoma (inhomogeneous appearance, irregular margins, HU > 20), additional testing of sex hormones (e.g., DHEAS) and steroid precursors should be performed. – Urology guideline. 10

Follow‑Up Imaging Protocol

• For radiologically benign lesions (<10 HU) that are <4 cm, no follow‑up imaging is required according to ACR and European Society of Endocrinology (ESE) guidelines. – ACR & ESE. [10][9]
• For radiologically benign lesions ≥4 cm, repeat imaging at 6–12 months is advised to assess for growth. – Urology guideline. 10
• The American Association of Clinical Endocrinologists/American Association of Endocrine Surgeons (AACE/AAES) recommend a more conservative schedule: re‑image at 3–6 months, then annually for 1–2 years. – Urology guideline. 10

Hormonal Surveillance

• ESE advises that no additional hormonal testing is needed if the initial workup is normal for hormonally inactive benign lesions. – Urology guideline. 10
• AACE/AAES and the Korean Endocrine Society (KES) recommend annual hormonal screening for 4–5 years, especially when the lesion exceeds 3 cm. – Urology guideline. 10

Management of Indeterminate Lesions

• Indeterminate lesions should be re‑imaged in 3–6 months. – Urology guideline. 10
• If the patient has a history of malignancy (e.g., lung, colon, lymphoma, neuroendocrine tumor), PET‑CT should be considered to further characterize the lesion. – Urology guideline. 10
• Surgical intervention is indicated when the lesion demonstrates growth >5 mm per year or any appreciable increase in size. – Urology guideline. 10

Key Pitfall

• Hormonal workup must not be omitted even when imaging suggests a benign adenoma, because 5–12 % of incidentalomas have subclinical hormone production. – ACR and Urology evidence. [8][10]