Evaluation of Small Adrenal Incidental Nodules: Is Imaging Follow-Up Necessary?

Abstract

Low incidence of adrenal cortical carcinoma in the general adult population has prompted a reevaluation of current protocol for the assessment of adrenal incidentalomas. To determine whether follow-up imaging for small (≤ 4 cm) incidental adrenal nodules is necessary for patients without known cancer. We performed a retrospective analysis of all patients found to have an incidental adrenal nodule on abdominal computed tomography (CT) scan during a 27-month period. The electronic medical record was reviewed to determine clinical outcomes in all patients with a minimum of 3 years of follow-up (mean follow-up = 6.7 years). Patients with a known primary cancer were excluded from the analysis unless they had a prior CT scan that documented an incidental adrenal nodule. Unenhanced CT attenuation was measured for all nodules, if available. A total of 392 patients with an incidental adrenal nodule had a mean (standard deviation [SD]) clinical follow-up of 6.7 (2.7) years. There were 200 men and 192 women with a mean (SD) age of 66.0 (13.2) years. None of these patients developed primary adrenocortical carcinoma during the follow-up period.Two hundred forty of these patients also had a minimum 3 years of imaging follow-up (mean [SD], 6.4 [2.4] years; range, 3.1-13.6 years). There were 173 left-sided and 91 right-sided nodules on index CT scan. There was no significant difference in the mean (SD) rate of growth between left- and right-sided nodules (0.1 [0.8] mm/year vs 0.1 [0.8] mm/year, p = 0.58). Mean unenhanced CT attenuation of adrenal nodules did not affect the likelihood of adrenal malignancy during follow-up. Patients with small incidental adrenal nodules do not require additional imaging to exclude the possibility of adrenocortical carcinoma.