Can abdominal CT features predict autonomous cortisol secretion in patients with adrenal nodules?

PURPOSE: To determine if CT features of adrenal nodules and of the remainder of the abdomen can predict autonomous cortisol secretion (ACH) in patients with adrenal nodules, and to identify a nodule size threshold below which ACH is unlikely. METHODS: Retrospective review of adult patients with adrenal nodules who underwent CT of abdomen and 1-mg Dexamethasone suppression test within 1 year of each other. Patients were considered to have no ACH if serum cortisol was ≤ 1.8 µg/dL after the 1-mg dexamethasone suppression test and to have possible or definite autonomous cortisol secretion if serum cortisol was > 1.8 µg/dL. The following CT features were assessed: Adrenal nodule length, nodule width, unenhanced nodule attenuation, contralateral adrenal gland thickness, visceral and subcutaneous adipose tissue area, skeletal muscle area and density, and unenhanced liver attenuation. RESULTS: 29 patients had no autonomous cortisol secretion and 29 patients had possible or definite autonomous cortisol secretion. Nodule length and width were the only two variables that significantly differed between patients with nonfunctional nodules and those with possibly or definitely functional nodules. Using a threshold nodule length of 1.5 cm, the sensitivity and specificity for predicting possible or definite autonomous cortisol secretion was 93.1% and 37.9%, respectively. CONCLUSION: Autonomous cortisol secretion in patients with adrenal nodules correlates with increasing nodule size. A nodule length threshold of 1.5 cm provides 93.1% sensitivity for predicting possible or definite ACH based on the 1-mg Dexamethasone suppression test.