Giant Adrenal Oncocytoma: A Case Report and Literature Review

ABSTRACT Introduction Adrenal oncocytomas are rare, nonfunctioning tumors composed of eosinophilic oncocytic cells whose nonspecific imaging often impedes preoperative diagnosis. We report a case of a large nonfunctioning adrenal oncocytoma with borderline malignant potential, incidentally discovered during cardiac symptom evaluation. Case Presentation A 77‐year‐old man with an incidentally discovered retroperitoneal tumor was referred to Urology for further evaluation. Contrast‐enhanced CT revealed a 93‐mm lobulated mass with heterogeneous enhancement abutting the left kidney's upper pole. Given the tumor's size, open left nephrectomy and adrenalectomy were performed. Gross and histopathology revealed a yellowish, solid adrenal tumor composed predominantly of oncocytic cells with no invasion of the kidney. Immunohistochemistry revealed a low Ki‐67 index (approximately 2%). The tumor was classified as having borderline malignant potential (Lin–Weiss–Bisceglia criteria). Conclusion We present a rare case of nonfunctioning adrenal oncocytoma with borderline malignant potential. Long‐term follow‐up is recommended due to the uncertain malignant potential.