Adrenocortical carcinoma (ACC) is an uncommon cause of adrenal incidentaloma (AI). ACCs generally occur in large sizes, >4 cm in diameter, at initial presentation and grow rapidly. Therefore, there have been few reports of cases with long-term follow-up with imaging before ACC was diagnosed. Herein, we present a case of an adrenal mass that had remained small and unchanged for 5 years but later grew rapidly and was finally diagnosed as ACC. A 77-year-old hypertensive woman was referred to our hospital for the examination of a 5.4-cm left adrenal mass. Upon reviewing her previous unenhanced computed tomography (CT) scan, a 1.6-cm and 30 Hounsfield units (HU), homogeneous, round, left adrenal mass was incidentally detected 9 years ago. This mass remained unchanged until 4 years ago. One year ago, the mass enlarged to 3.0-cm and changed into an irregular form with heterogeneous density. The hormonal evaluation during the 9 years from the discovery of the AI was inadequate. The present examination diagnosed this case as ACC with subclinical Cushing's syndrome. The patient underwent laparoscopic left adrenalectomy, and a histological diagnosis of high-grade ACC was made. The resected tumor had the CTNNB1 gene mutation. High unenhanced CT attenuation values (>10 HU) are one of the findings that raise suspicion of malignancy. This case suggests that patients with findings atypical of adenomas on an initial unenhanced CT might be carefully followed up given the possibility of development of ACCs, even if the initial tumor size is small.
Keywords: Adrenal incidentaloma; Adrenocortical carcinoma; Computed tomography.