What are the follow-up recommendations for a 1.5 cm adrenal adenoma with a density of 77 Hounsfield Units (HU)?

From the Guidelines

For a 1.5 cm adrenal adenoma with a density of 77 Hounsfield Units (HU), the recommended follow-up includes biochemical evaluation for hormonal activity and repeat imaging in 6-12 months, as suggested by the most recent guidelines 1. The high density (>10 HU) raises concern for a non-adenoma lesion such as pheochromocytoma, metastasis, or adrenocortical carcinoma. Biochemical testing should include:

• Plasma free metanephrines or 24-hour urinary metanephrines to rule out pheochromocytoma
• Serum aldosterone and plasma renin activity to assess for hyperaldosteronism
• A 1mg overnight dexamethasone suppression test to screen for hypercortisolism, as recommended by the guidelines 1. If the patient has a history of malignancy, this lesion should be considered suspicious for metastasis until proven otherwise. Follow-up imaging with contrast-enhanced CT or MRI can help evaluate for enhancement pattern and washout characteristics. If the lesion grows more than 0.8-1 cm during follow-up or shows concerning features on subsequent imaging, surgical consultation for possible adrenalectomy should be considered. This approach is justified because the high density significantly exceeds the 10 HU threshold typically used to differentiate benign adenomas from other adrenal masses, necessitating closer monitoring and comprehensive evaluation, in line with the recommendations from the guidelines 1. The guidelines also emphasize the importance of a multidisciplinary review for cases with uncertain diagnosis or significant growth, which supports the consideration of surgical consultation if concerning features are identified 1. In contrast to older guidelines, the most recent recommendations prioritize a more individualized approach based on the specific characteristics of the adrenal mass and the patient's clinical context, as seen in the discussion of various guidelines 1. However, the key principle of close monitoring and comprehensive evaluation for lesions with high density, such as the one in question, remains consistent across the guidelines.

From the Research

Adrenal Adenoma Follow-up Recommendations

The follow-up recommendations for a 1.5 cm adrenal adenoma with a density of 77 Hounsfield Units (HU) can be based on the following guidelines:

• For masses that appear to be benign, small, and completely nonfunctioning, imaging and biochemical reevaluation at 1-2 years is appropriate 2.
• However, since the density of the adenoma is 77 HU, which is higher than the typical threshold for benign adenomas (<10 HU), repeat evaluation for growth after 3-12 months may be useful 2.
• The growth pattern of adrenal masses can be variable, and surveillance over 2 years may detect only 50% of adrenocortical cancers 3.
• Biochemical testing for pheochromocytoma and hypercortisolism should be performed, especially if the patient has symptoms suggestive of these conditions 2.

Imaging Characteristics

The imaging characteristics of the adrenal adenoma can help guide follow-up recommendations:

• A density of 77 HU on unenhanced CT is higher than the typical threshold for benign adenomas (<10 HU) 4, 5.
• The use of CT histogram analysis may provide higher sensitivity than the commonly used 10 HU threshold mean attenuation method for diagnosing adenomas 4.
• Combined unenhanced and delayed enhanced CT can correctly characterize nearly all adrenal masses as adenomas or non-adenomas 5.

Histopathologic Correlation

The correlation between imaging characteristics and histopathologic findings can help guide follow-up recommendations:

• Imaging characteristics can predict the presence of benign lesions with 100% specificity 6.
• Every adrenal malignancy had CT or MR results that were inconsistent with benign adenoma (100% sensitivity) 6.
• Adrenal masses with non-benign imaging characteristics should be resected to exclude malignancy 6.