How should a 1.7 cm homogeneous, well‑circumscribed adrenal incidentaloma without Hounsfield‑unit measurement on CT be evaluated and managed?

Management of a 1.7 cm Homogeneous Adrenal Incidentaloma Without HU Measurement

Your patient requires immediate dedicated adrenal imaging with a non-contrast CT to measure Hounsfield units (HU), which is the essential first step before any management decisions can be made. 1, 2

Why HU Measurement is Mandatory

Without HU measurement, you cannot determine whether this lesion is benign or requires further workup. The current imaging is inadequate for proper risk stratification. 3

• If HU ≤10: The lesion is definitively a benign lipid-rich adenoma requiring no further imaging workup, regardless of the homogeneous appearance. 2, 3
• If HU >10: The lesion is indeterminate and requires second-line imaging with either washout CT or chemical shift MRI. 1, 2

Complete Hormonal Evaluation (Perform Immediately)

While arranging the non-contrast CT, initiate hormonal screening now—do not wait for imaging results. 1, 3

• Screen for pheochromocytoma with plasma or 24-hour urinary metanephrines in all patients. This is mandatory before any surgical decision or biopsy to prevent life-threatening hypertensive crisis. 1, 2, 3
• Perform 1 mg overnight dexamethasone suppression test to exclude autonomous cortisol secretion (cutoff: serum cortisol ≤50 nmol/L or ≤1.8 µg/dL). 1, 3, 4
• Check aldosterone-to-renin ratio only if the patient has hypertension or unexplained hypokalemia. 5, 3

Management Algorithm After HU Measurement

If HU ≤10 (Benign Adenoma)

• No further imaging is needed for this 1.7 cm lesion if hormonal workup is normal. 2, 3
• Some guidelines recommend no follow-up imaging at all for benign, non-functioning masses. 5
• More conservative approaches suggest repeat imaging at 12 months, then discharge if stable and <2 cm. 5

If HU >10 (Indeterminate Lesion)

• Obtain washout CT or chemical shift MRI as second-line imaging. 1, 2
• Washout CT protocol: Calculate relative percentage washout = [1 – (delayed HU / dynamic HU)] × 100%. Washout >50% indicates benign adenoma; <50% suggests possible malignancy. 2
• Chemical shift MRI: Signal loss on out-of-phase images compared to in-phase identifies benign adenoma with 89% accuracy for lesions 10-30 HU. 2, 6

If Imaging Remains Indeterminate After Second-Line Studies

• Shared decision-making between repeat imaging in 3-6 months versus surgical resection after completing full hormonal workup. 1
• For non-functional lesions <4 cm with indeterminate imaging, repeat imaging in 3-6 months is the preferred conservative approach. 1
• If growth is >5 mm/year on follow-up, repeat functional workup and consider adrenalectomy. 1

Size-Based Risk Stratification

At 1.7 cm, this lesion falls into the low-risk category for malignancy. 2, 7

• Lesions <3 cm are most often benign and extensive workup beyond HU measurement and hormonal screening is generally not justified. 2, 7
• Lesions >4 cm have higher malignancy risk and typically warrant more aggressive evaluation or surgery. 3, 4

Critical Pitfalls to Avoid

• Never proceed with any intervention before excluding pheochromocytoma, as undiagnosed pheochromocytoma can cause life-threatening hypertensive crisis during surgery or biopsy. 1, 2
• Never perform adrenal biopsy for routine workup—it is rarely indicated and carries risks including tumor seeding and hemorrhage. 1, 2, 3
• Do not rely on "homogeneous" and "well-circumscribed" descriptors alone—approximately one-third of benign adenomas and some malignant masses can appear homogeneous, making HU measurement essential. 1
• Do not skip hormonal evaluation even if imaging ultimately shows benign characteristics—functional testing is mandatory regardless of imaging appearance. 6, 3

Nuances in Guideline Recommendations

There is significant variation among professional societies regarding follow-up protocols for benign, non-functioning masses. 5

• ESE and ACR guidelines: No follow-up imaging needed for confirmed benign masses. 5
• AACE/AAES guidelines: Reimage at 3-6 months, then annually for 1-2 years. 5
• CUA and KES guidelines: Single repeat imaging at 12 months, then clinical follow-up. 5

Given the low malignancy risk at 1.7 cm and if imaging confirms benign features (HU ≤10) with normal hormonal workup, the most evidence-based approach is minimal or no imaging follow-up. 3