Management of Benign Adrenal Incidentalomas (≤4 cm)

Initial Imaging Assessment

• An unenhanced CT attenuation < 10 HU definitively confirms a benign lipid‑rich adrenal adenoma, eliminating the need for further imaging or functional testing. [1][2]
• When the original study was contrast‑enhanced only or attenuation values are unavailable, a non‑contrast CT should be obtained first to measure HU. [1][3]

Hormonal Evaluation (Required for All Incidentalomas)

• Every patient with an adrenal incidentaloma must be screened for hormone excess, regardless of imaging appearance. [1][3]
• Cortisol excess: Perform a 1‑mg overnight dexamethasone suppression test; cortisol should suppress to ≤1.8 µg/dL (≤50 nmol/L). [1][3]4
• Pheochromocytoma: Measure plasma or 24‑hour urinary fractionated metanephrines; testing may be omitted only if the CT shows < 10 HU and the patient has no catecholamine‑related symptoms. [1][3]
• Primary aldosteronism: Obtain an aldosterone‑to‑renin ratio in patients with hypertension and/or hypokalemia. [1][3]

Management When Imaging < 10 HU and Hormonal Tests Are Normal

• No additional imaging follow‑up or functional testing is required. 2
• The 2023 CUA/AUA guidelines state that benign, non‑functional adrenal adenomas < 4 cm do not need any surveillance. 2

Surveillance for Indeterminate Lesions (Imaging ≥ 10 HU, Size < 4 cm, Non‑Functional)

• Repeat imaging at 6–12 months. 2
• If growth is < 3 mm/year on follow‑up, discontinue further imaging. 2
• If growth exceeds 5 mm/year, consider adrenalectomy after repeating functional work‑up. 2

Management of Mild Autonomous Cortisol Secretion (MACS)

• Screen for cortisol‑related comorbidities (e.g., hypertension, diabetes, osteoporosis, weight gain). 4
• In younger patients with progressive metabolic complications attributable to cortisol excess, adrenalectomy may be offered after shared decision‑making. [1][2]
• If surgery is not pursued, conduct annual clinical screening for new or worsening comorbidities. 1

Management of Clearly Functional Adenomas

• Cortisol‑secreting adenoma with overt Cushing’s syndrome: Perform unilateral minimally‑invasive adrenalectomy. [1][2]
• Pheochromocytoma: Proceed with unilateral adrenalectomy after appropriate pre‑operative alpha‑blockade. 1

Common Pitfalls to Avoid

• Do not assume “adenoma” is benign without confirming unenhanced CT attenuation < 10 HU; about one‑third of adenomas are lipid‑poor and may have higher attenuation. [1][2]
• Do not skip hormonal evaluation based solely on imaging, because functional adenomas can appear identical to non‑functional lesions on CT. [1][3]
• Adrenal biopsy is rarely indicated and is contraindicated when pheochromocytoma has not been excluded. [1][3]
• Once the criteria for a benign, non‑functional adenoma are met, the patient should be discharged from follow‑up. 2

Special Considerations for “Unchanged” Lesions

• If the lesion has been stable for 1–2 years with documented growth < 3 mm/year and the initial hormonal work‑up was normal, no further imaging or hormonal surveillance is needed. [2][4]
• Earlier (2009) AACE recommendations called for annual imaging for 1–2 years and yearly hormonal testing for 5 years, but the 2023 CUA/AUA guidelines have simplified this to no surveillance for benign, non‑functional adenomas < 4 cm. [4][2]

Imaging Evaluation of Adrenal Incidentalomas

Initial Non‑Contrast Assessment

• Non‑contrast CT (NCCT) is the primary first‑line study for any adrenal lesion, with attenuation measured in Hounsfield units (HU). The American College of Endocrinology and the American Association of Clinical Endocrinology recommend this approach. 5
• A lesion ≤10 HU on NCCT and appearing homogeneous is highly specific for a benign lipid‑rich adenoma (98 % specificity); all malignant lesions exceed 10 HU. This threshold provides near‑perfect rule‑out of cancer. 6

When a Dedicated Dynamic CT Protocol Is Needed

• If NCCT attenuation is >10 HU, a three‑phase dedicated adrenal CT protocol should be performed (non‑contrast, venous phase at 60–70 s, and delayed phase at ~15 min). This recommendation comes from the American College of Endocrinology and the American Association of Clinical Endocrinology. 5
• Dynamic imaging enables calculation of contrast washout, which helps differentiate adenomas from non‑adenomatous masses. 6

Limitations of Routine Single‑Phase CT

• Standard abdominal CT that includes only a single venous‑phase acquisition is not advised for characterizing known adrenal lesions. The same endocrine societies advise against its use. 5

Pitfalls of CT Washout Analysis

• Up to 35 % of pheochromocytomas and certain metastases (e.g., renal‑cell or hepatocellular carcinoma) can mimic adenoma washout patterns, potentially leading to misclassification. 7

MRI as the Preferred Second‑Line Modality

• Current endocrine guidelines favor MRI over contrast‑enhanced CT when further imaging is required after NCCT. 7
• MRI with chemical‑shift imaging (CSI) detects intracellular lipid without ionizing radiation. This technique is endorsed by the American College of Endocrinology and the American Association of Clinical Endocrinology. 6
• MRI is especially valuable for heterogeneous adrenal lesions, where dynamic CT performance is suboptimal. 8
• MRI is the modality of choice for younger patients needing surveillance, as well as for pediatric and pregnant patients. 8

Practical Imaging Algorithm (Evidence‑Based)

CT Washout Imaging for Adrenal Lesion Characterization

Definition & Technical Protocol

• CT washout is a dedicated three‑phase adrenal CT technique that quantifies how quickly intravenously administered contrast leaves an adrenal lesion, using attenuation values from non‑contrast, venous (60–70 s), and delayed (≈15 min) phases. 9
• The protocol requires:
• Single‑phase abdominal CT scans are insufficient for adrenal lesion characterization and should not be employed for this purpose. 9, 10

Clinical Rationale & Interpretation

• Benign adrenal adenomas typically exhibit marked early enhancement followed by rapid contrast loss because of normal vascular architecture, whereas malignant lesions display slower washout due to abnormal vasculature. 9, 10

Indications for Performing CT Washout

• CT washout should be performed only when a homogeneous adrenal lesion shows non‑contrast attenuation > 10 HU; lesions ≤ 10 HU are considered lipid‑rich benign adenomas and do not require contrast imaging. 9, 10

Limitations & Pitfalls

• Up to 35 % of pheochromocytomas may meet adenoma‑type washout criteria, leading to false‑negative results. 9, 11, 12
• Hypervascular metastases, especially from renal cell carcinoma and hepatocellular carcinoma, can mimic adenoma washout patterns, risking false‑positive classification. 9, 11

Current Guideline Recommendations (ACE/AACE)

• The American College of Endocrinology and the American Association of Clinical Endocrinologists now recommend MRI with chemical‑shift imaging (CSI) over contrast‑enhanced CT washout when additional imaging is needed after a non‑contrast CT. 9, 11 – Strong guideline recommendation.

Situations Where CT Washout May Still Be Considered

• When the adrenal lesion is homogeneous on imaging, CT washout can be used to “rule‑in” a benign tumor. 9

Mandatory Biochemical Evaluation

• Because pheochromocytoma cannot be excluded by imaging alone, plasma or urinary fractionated metanephrines must be obtained before any adrenal biopsy or intervention. 12 – Strong clinical recommendation.

Alternative Imaging Modality

• MRI with chemical‑shift imaging detects intracellular lipid without ionizing radiation and is now the preferred method for indeterminate adrenal lesions. 9, 11 – Guideline‑endorsed.
• CSI is especially valuable for heterogeneous lesions, where CT washout performance is suboptimal. 9, 11

All facts are drawn from peer‑reviewed sources cited above; strength of evidence is indicated where explicitly provided by the guideline statements.