Follow-up for Low Density Bilateral Adrenal Nodules

Radiological Characteristics and Risk Assessment

Adrenal nodules with Hounsfield units (HU) less than 10 on unenhanced CT are considered benign regardless of size, with those less than -10 HU representing lipid-rich adenomas with even higher confidence of benignity, as per the American College of Radiology 3, 4
The threshold value of 10 HU has been established as a reliable means of distinguishing benign from malignant adrenal tumors, with values below this threshold strongly indicating benign lesions, according to the National Comprehensive Cancer Network 5, 6

For nodules <4 cm with HU <10 (especially those <-10 HU), no further imaging follow-up is recommended as per current guidelines from the American Urological Association 2, 7
Each nodule in bilateral adrenal incidentalomas should be separately characterized, but the same follow-up principles apply to each nodule, as stated by the American Urological Association 8

In bilateral adrenal incidentalomas, consider measuring serum hormone levels to exclude congenital adrenal hyperplasia, as recommended by the American Urological Association 8
Assessment for adrenal insufficiency should be considered in cases of bilateral infiltrative disease, though this is extremely unlikely with nodules <-10 HU, according to the American Urological Association 8

The 2023 Canadian Urological Association/American Urological Association guidelines explicitly state that patients with benign non-functional adenomas <4 cm, myelolipomas, and other small masses containing macroscopic fat detected on the initial work-up for an adrenal incidentaloma do not require further follow-up imaging or functional testing, as per the American Urological Association 2

If either nodule is ≥4 cm despite having HU <-10, a single repeat imaging in 6-12 months may be considered due to the slightly higher risk associated with larger size, as recommended by the American Urological Association 1
Growth >5 mm/year on any follow-up imaging would warrant consideration for adrenalectomy after repeating functional work-up, according to the American Urological Association 1

Avoid assuming all bilateral adrenal nodules represent metastatic disease; bilateral adenomas are common, especially in older patients, as noted by the American Urological Association 7
Do not confuse the management of lipid-rich adenomas (HU <10) with indeterminate adrenal masses (HU >10), which require more extensive follow-up, as per the American College of Radiology 3, 4