OBJECTIVE Recently, the European Society of Endocrinology (ESE), in collaboration with the European Network for the Study of Adrenal Tumors (ENSAT), asserted that adrenal incidentalomas (AIs) <4 cm and ≤10 Hounsfield units (HU) do not require further follow-up imaging. To validate the clinical application of the follow-up strategies suggested by the 2016 ESE-ENSAT guidelines, we explored the clinical characteristics and natural course of AIs in a single center over 13 years.

DESIGN AND METHODS This retrospective cohort study included a total of 1149 patients diagnosed with AIs between 2000 and 2013 in a single tertiary center. Hormonal examination and radiological evaluations were performed at the initial diagnosis of AI and during the follow-up according to the appropriate guidelines.

RESULTS The mean age at diagnosis was 54.2 years, and the majority of AIs (68.0%) were nonfunctional lesions. Receiver operating curve analysis was used to discriminate malignant from benign lesions; the optimal cut-off value for mass size was 3.4 cm (sensitivity: 100%; specificity: 95.0%), and that for the pre-contrast HU was 19.9 (sensitivity: 100%; specificity: 67.4%). The majority of nonfunctional lesions did not change in size during the 4-year follow-up period. Applying a cut-off value of 1.8 μg/dL after a 1-mg overnight dexamethasone suppression test, 28.0% of all nonfunctional AIs progressed to autonomous cortisol secretion during the follow-up period. However, we observed no development of overt Cushing's syndrome in the study.

CONCLUSIONS We advocate that no follow-up imaging is required if the detected adrenal mass is <4 cm and has clear benign features. However, prospective studies with longer follow-up are needed to confirm the appropriate follow-up strategies.