Oncocytic tumors originating from the adrenal cortex are extremely rare. To date, only 46 cases have been reported, and include 24 oncocytomas, 6 oncocytic neoplasms of uncertain malignant potential and 16 oncocytic carcinomas. The patients had a wide age range (27 to 74 years) with a significant female to male predominance. The neoplasms varied in size from 2.2 cm to 15 cm and in weight from 22 g to 865 g. All arose in the adrenal gland with the exception of two cases, which occurred in heterotopic retroperitoneal adrenal tissue [4,5]. Patients were usually not initially referred to an oncologist. In all but one case, oncocytic neoplasms were diagnosed incidentally or during investigation for symptoms that were not attributable to the tumor, such as abdominal pain, hematuria, essential hypertension, episodic vomiting, ascites and edema of the lower extremities [6,7]. El-Naggar et al. [8] reported the case of one patient who suffered from abdominal pain caused by tumor infiltration to the adjacent vena cava and liver.

Oncocytic neoplasms of the adrenal cortex were non-functioning with the exception of two cases. Xiao et al. [9] identified an adrenocortical oncocytoma in a 53-year-old woman who presented with Cushing's syndrome. Erlandson and Reuter [10] reported a female patient who was incidentally found to have a 5 cm virilizing adrenocortical oncocytoma and a coexisting urinary bladder tumor. After surgery, this patient's 17-ketosteroid level returned to normal.

Our patient had a functioning adrenocortical oncocytic neoplasm. He was symptomatic and admitted to the hospital because of suspected Cushing's syndrome. The laboratory findings were compatible with the syndrome, and further investigation revealed a mass in the right adrenal gland. After the surgery, the Cushing's syndrome resolved.

The biologic behavior of adrenocortical neoplasms is the most important practical problem. A combination of clinical, biochemical and histological features can differentiate benign and malignant adrenocortical tumors. Aside from the obviously malignant cases in which the diagnosis is based on common clinicopathologic features universally valid for tumors of any site, such as distant metastases, surgical unresectability and/or invasion of adjacent organs, the prediction of biologic behavior and clinical outcome can be difficult. There is no single histological parameter that is predictive of the clinical outcome and biologic behavior of adrenocortical oncocytic neoplasms. The Weiss system is the most widely used and accepted histological scheme to distinguish benign from malignant adrenal tumors [11]. According to this system, the presence of four or more of the nine criteria (high mitotic rate, atypical mitoses, high nuclear grade, low percentage of clear cells, necrosis, diffuse tumor architecture, capsular invasion, sinusoidal invasion and venous invasion) indicates a malignant neoplasm. However, the Weiss criteria have limitations. First, Weiss studied only 43 adrenocortical tumors of which 25 were benign and 18 were malignant tumors according to his classification. Second, patients with benign tumors in his series had a longer follow-up period than those with malignant tumors. Third, tumor tissue could be heterogeneous within the same lesion. Therefore, the Weiss score, even if established by experienced pathologists, cannot be completely reliable. Pohlink et al. [12] reported a patient with an adrenal incidentaloma, which was initially diagnosed as benign but on follow-up was reclassified as malignant because of local recurrence and pulmonary metastases.