Pathologic analysis of adrenocortical oncocytic adenomas with report of 7 cases

Objective To analyze the diagnosis criteria, the significance of Weiss system and the differential diagnosis of adrenocortical oncocytic adenomas. Methods The morphologic, immunohistochemical and electron microscopic examinations were carried out in 7 cases of adrenocortical oncocytic adenomas, and the associated literatures were reviewed. Results All the tumors of the 7 cases were predominantly composed of the oncocytic epithelial cells, which arranged mainly in a diffuse architectural pattern and some in alveolar, tubular and trabecular patterns. The immunohistochemical examination showed that the expressions of vimentin and neuron-specific enolase were strongly positive, and the S-100 protein expression was slightly positive in almost all the cases. The expressions of chromogranin-A and synaptophysin were slightly positive in partial cases. And the expressions of AE1/3, melan-A,inhibin-α,CD10 and P53 were negative in nearly all the cases. The positive rate of MIB-1 was less than 5%. The electron microscopic studies showed that the cytoplasm of the oncocytes was packed with abundant mitochondria. Conclusions The criteria modified from the traditional Weiss system are proposed as following, if an oncocytic tumor exhibits a mitotic rate of more than 5 mitoses per 50 high power fields or any atypical mitoses or venous invasion (defined as major criteria), it is considered as malignant; if the tumor exhibits 1 or several other worrisome features ( the size 10 cm and/or the weight 200 g, with necrosis, capsular invasion, or sinusoidal invasion)(defined as minor criteria), the tumor is considered as uncertain malignant potential (borderline); if none of the above features is present, the tumor is benign. Depending on the modified Weiss system, the diagnosis of all these 7 cases with AOA was unambiguous and none of these patients recurred or had any metastasis. The differential diagnosis of AOA includes the following entities: oncocytic pheochromocytoma, adrenocortical carcinoma exclusively composed of compact cells, adrenocortical carcinoma with focal oncocytic changes, renal carcinoma with oncocytic features, and eosinophilic variant of chromophobe renal carcinoma involving the adrenal and hepatocellular carcinoma.