Autonomy of cortisol secretion in clinically silent adrenal incidentaloma

Recent progress in non-invasive imaging techniques have resulted in an incr easing frequency of adrenal incidentaloma discovery. In addition, even clin ically silent adrenal tumor has been suggested to possess a subtle producti on of adrenal hormones. The aim of the study was to ascertain the autonomy of cortisol production in clinically silent adrenocortical incidentaloma. W e investigated the hypothalamic-pituitary-adrenal axis in 38 patients with adrenal incidentaloma. Basal plasma cortisol level was reproducibly within normal range in all the patients with adrenal incidentaloma, but was also n ormal in half of the Cushing's syndrome cases studied. Eighteen of 38 patie nts showed plasma cortisol above 3 mug/dl after 1 mg dexamethasone (Dex) an d above 1 mug/dl after 8 mg Dex, respectively, and were defined as preclini cal Cushing's syndrome. These patients were subjected to further evaluation of the autonomy of cortisol production. The incidence of positive findings indicating autonomy of cortisol secretion was as follows: suppressed basal plasma ACTH level in 44%, loss of normal diurnal rhythm in 79%, lack of AC TH response to CRF in 35%, decreased plasma DHEA-S level in 28%, significan t laterality of I-131-aclosterol uptake in 75%, atrophy of the contralatera l side of the adrenal on CT scan in 6%, and histological atrophy of the adj acent adrenal cortex in 56%, respectively. The endocrine feature relevant t o the hypothalamic-pituitary-adrenal axis varied from patient to patient, r anging from the non-functioning adrenal adenoma to Cushing's syndrome. in a ddition, the results of each test did not coincide with others in each pati ent. These results clearly demonstrated that the incidence of autonomy of c ortisol production in the clinically silent adrenal incidentaloma is not in frequent, showing significant diversity. Systemic evaluation of the hypotha lamic-pituitary-adrenal axis before adrenal surgery is warranted for an app ropriate glucocorticoid replacement after adrenal surgery.