Reviews and CommentaryFree Access

Incidental Adrenal Lesions May Not Always Require Further Imaging Work-up

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See also the article by Kim et al in this issue.

Dr Baumgarten is a professor of abdominal radiology at the Mayo Clinic Jacksonville. Her clinical interests include cost-effective imaging, reducing unnecessary imaging, the genitourinary system, the thyroid, and the postoperative neck. She is a fellow of the American College of Radiology and the Society of Abdominal Radiology, volunteers with numerous national organizations, including serving on the Executive Council of the American Roentgen Ray Society and the editorial board of Radiology.

Dr Baumgarten is a professor of abdominal radiology at the Mayo Clinic Jacksonville. Her clinical interests include cost-effective imaging, reducing unnecessary imaging, the genitourinary system, the thyroid, and the postoperative neck. She is a fellow of the American College of Radiology and the Society of Abdominal Radiology, volunteers with numerous national organizations, including serving on the Executive Council of the American Roentgen Ray Society and the editorial board of Radiology.

Incidental findings are defined as those discovered at imaging for a reason unrelated to the clinical question that prompted the imaging. Adrenal incidentalomas (unexpected adrenal lesions ≥1 cm) are one of the most frequently encountered incidental findings, occurring in 1%–6% of adults (1). Given their relatively common occurrence, many well-respected national medical associations have attempted to gather scientific evidence and expert opinion to help guide their further work-up or follow-up. A recent article (2) highlighted the differences between five sets of recommendations published by the American College of Radiology (ACR) (3), the Canadian Urological Association (4), the European Society of Endocrinology (5), the American Association of Clinical Endocrinologists/American Association of Endocrine Surgeons (AACE/AAES) (6), and the Korean Endocrine Society (KES) (7). While all agree that a mass with an unenhanced attenuation of 10 HU or less is adequately characterized as benign, that patients should undergo hormonal evaluation to exclude a cortisol-secreting adenoma or a pheochromocytoma, and that no surgery is necessary for a benign nonfunctioning mass, the need for follow-up imaging of a benign mass remains controversial. The European Society of Endocrinology and the ACR agree that no follow-up imaging is needed if the mass is characterized as benign at initial imaging (3,5); however, other society guidelines vary in the frequency of recommended follow-up, from (a) one follow-up examination in 12 months and no further imaging if the mass is stable to (b) 3–6-month initial follow-up imaging and annual imaging for 1–2 years thereafter (4,6,7). All guidelines consider surgery appropriate for lesions that are clearly metastatic, with metastatic disease isolated to the adrenal gland (37). For lesions 4 cm or larger in patients without cancer history, the ACR, KES, and AACE/AAES recommend resection (3,6,7). The sheer number of different recommendations and the fact that guidelines put forth by radiology societies differ from those put forth by clinical societies is nothing short of confusing.

Further confusing the issue are adrenal incidentalomas that are not adequately characterized at initial imaging—those that are neither benign nor definitively worrisome based on size or other characteristics. The evaluation of indeterminate masses in society guidelines is even more variable, including recommendations for immediate surgery, immediate alternative imaging for possible definitive characterization, or interval follow-up imaging to assess a change in size (37). But do we need to do anything at all with these? These are the types of lesions that would be discovered at staging CT for potentially resectable gastric cancer—CT examinations that generally do not include noncontrast imaging (helpful for characterizing lipid-rich adenomas) and do not produce delayed images allowing for determination of washout characteristics (helpful for characterizing some lipid-poor adenomas).

It is in this population that this very question was asked and investigated by Kim et al (8). Their population included 10 250 patients with potentially resectable gastric cancer. All 10 250 scans were reassessed with a picture archiving and communication system to determine the presence or absence of an adrenal mass at least 1 cm in size, and the original radiology reports were reviewed for a second evaluation. Among the 10 250 patients, the investigators found 522 adrenal incidentalomas in 462 (5%) patients, well in line with that expected in the general population based on prior investigations. In only two patients did five nodules turn out to be malignant—both patients had prior or concurrent malignancy (one lung, one hepatocellular carcinoma). Therefore, 517 nodules in 460 patients were benign. When reviewing the original reports, only 272 of the 10 250 patients were reported to have an adrenal nodule, and both patients with malignant nodules were included. Most of the nodules not reported measured 10–15 mm. Given the difference in the number of nodules discovered when the reports were re-reviewed versus the number of nodules originally reported, Kim et al (8) postulated that many of these nodules were ignored by the original reporting radiologist as likely benign—something I am sure we have all done depending on the clinical situation. Keep in mind that early stage potentially resectable gastric cancer rarely, if ever, would metastasize to the adrenal glands before metastatic disease would be noted elsewhere (liver, peritoneum). So, our gut feeling that small adrenal nodules are overwhelmingly benign is correct.

For adrenal nodules found at re-review, 123 of 462 patients (27%) underwent further evaluation (65 excisional biopsy, 25 imaging, 95 biochemical tests). Clearly some of these nodules were not initially mentioned, so it is unsurprising that not all nodules had additional work-up. Interestingly, not even all the indeterminate nodules mentioned on the original CT report were further investigated. Since the authors are from Korea, the KES guidelines would be the ones most likely to have been followed, and they recommend all nodules undergo biochemical evaluation as well as noncontrast CT to try to prove benignity (7). However, Kim et al (8) found that only 116 of the 272 patients with nodules mentioned in the original report (43%) underwent any kind of further adrenal examination (63 excisional biopsy, 24 imaging, and 88 biochemical tests). Thus, in this series, the guidelines were not followed more than 50% of the time.

Why are the guidelines not followed? One of the factors investigated by Watari et al is the wording in the radiology report—that is, how we as radiologists report findings influences, whether they will be investigated further, and how (9). In their article that included 11 723 CT scans including the adrenal gland, 246 patients were reported to have an adrenal incidentaloma (only reports were evaluated; other patients may have had adrenal lesions that were not reported, similar to Kim et al). Only 63 of the 246 reports mentioned the need for any follow-up. A total of 38 of 246 (15.4%) patients were referred for evaluation. Although nodule size, patient age, and subspecialty of the referring provider also were examined, only the presence of a radiology report recommending additional evaluation was significantly associated with such a referral (odds ratio, 5.441; 95% CI: 2.491, 11.887). These authors concluded that including guideline-driven recommendations for further evaluation and follow-up might help improve adherence to guidelines.

But what if we do not need to follow these guidelines? What if the guidelines are merely driving additional unnecessary imaging? Kim et al (8) suggest that in their population of patients with early resectable gastric cancer where no case of malignancy was missed and none of the malignant nodules were related to gastric cancer, no amount of follow-up imaging related to the adrenal incidentalomawould drive a change in patient care. Further, as addressed in the Discussion, even in patients who underwent additional imaging for lesion characterization “differentiation of malignant versus benign nodules remained inconclusive in a quarter of the patients.” They conclude that our current guidelines do not adequately address the low incidence of malignant adrenal nodules in patients with resectable gastric cancer and should be revised. I wonder if we can take their data and extrapolate it to patient populations at even less risk of malignant adrenal nodules: those with no cancer history at all. If the incidence of malignant nodules in a population with cancer (albeit a cancer that would rarely metastasize to the adrenal gland when still resectable) is nearly zero (and the nodules that were malignant were in patients with other cancers and were easily detected), then the incidence of malignant nodules in a population without cancer should also be nearly zero.

I think it’s time to look more closely at our guidelines.

Disclosures of Conflicts of Interest: D.A.B. is on the editorial board of Radiology.


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  • 9. Watari J, Vekaria S, Lin Y, et al. Radiology report language positively influences adrenal incidentaloma guideline adherence. Am J Surg 2021. Published online June 29, 2021.

Article History

Received: Aug 18 2021
Revision requested: Aug 25 2021
Revision received: Aug 25 2021
Accepted: Aug 27 2021
Published online: Oct 19 2021
Published in print: Jan 2022