a 69-year - old male with no significant medical history presented to the hospital with abdominal discomfort that had lasted for about 1 month . there were no specific findings on the physical examination except for palpation of the abdominal mass . an 18.212.316.9 cm mixed solid and cystic mass lesion was observed in the retroperitoneal space on a computed tomography ( ct ) image of the abdomen and pelvis ( fig . open abdominal biopsy of the mass was conducted in the hospital in october 2010 and the mass was identified as an adrenocortical neoplasm , but the adrenal mass could not be differentiated from carcinoma or adenoma . preoperative positron emission tomography - ct ( pet - ct ) showed a huge , necrotic , suprarenal mass with fludeoxyglucose uptake . the patient underwent a left radical adrenalectomy , and the mass showed hypervascularity and severe adhesion to the surrounding tissues . postoperative pathological examination showed necrosis and that less than 25% of the tumor cells were clear cells ( fig . this case was thus diagnosed as an oncocytic adrenocortical tumor with uncertain malignant potential according to the weiss system . the postoperative course showed no specific findings , and the patient was discharged on the 9th day after the operation . a follow - up pet - ct around 3 months after surgery showed no recurrence of the tumor ( fig . most lesions are asymptomatic and are detected incidentally on evaluation for abdominal pain or hypertension . oncocytoma consists of oncocytes , which are acidophilic epithelial cells that show accumulation of mitochondria in the cytoplasm on electron microscopy . peppa et al reported 53 cases of adrenocortical oncocytoma ; in that series , the age at diagnosis of adrenocortical oncocytoma ranged from 15 to 77 years and the ratios of males to females and of left to right were 1:2.5 and 3.5:1 , respectively . the size and weight of the tumors were 3 to 17 cm and 30 to 1,800 g , respectively . the distribution of benign , borderline , and malignant cases were 28 , 14 , and 11 , respectively . to discriminate between benign and malignant tumors , size and weight have been emphasized as predictors of biological behavior . these are not accurate parameters , however ; accordingly , other systems such as the combination of clinical , biochemical , and histological features have been used to distinguish between benign and malignant tumors . in particular , the weiss system is widely used , which assesses a total of nine histologic features ; fuhrman nuclear grade , mitotic rate > 5 per 50 high power field , atypical mitoses , clear cell composition less than 25% of the entire tumor mass , diffuse architecture , necrosis , venous invasion , sinusoidal invasion , and capsular invasion . cases meeting zero , two , or more of these criteria and the others are classified into benign , malignant , and borderline of uncertain malignant potential , respectively . in addition , the immunohistochemical and molecular profile is used to investigate the nature of tumors . this profile evaluates immunoreactivity to anti - mitochondrial antibody mes-13 , vimentin , inhibin , and melan a. however , its usefulness for diagnosis is limited because of low immunohistochemical sensitivity . our case was interesting because malignancy was clinically suspected before the operation , but the mass was found to be an oncocytic adrenocortical tumor with uncertain malignant potential through postoperative histologic assessment . the immunohistochemical findings from preoperative biopsy were as follows : positive for cytokeratin , synaptophysin , inhibin , and melan a. moreover , because an 18.212.316.9 cm large , mixed solid and cystic mass associated with necrosis was observed on the abdomen - pelvis ct image , malignancy was clinically suspected . oncocytic adrenocortical tumors with uncertain malignant potential are a rare neoplasm and their clinical significance and management are uncertain . therefore , review of similar borderline tumors is necessary . one such tumor is the prostatic stromal tumor of uncertain malignant potential , or stump . fukuhara et al reported that most stumps do not show aggressive behavior but did recur or progress to stromal sarcoma after resection in a few cases . therefore , an oncocytic adrenocortical tumor with uncertain malignant potential as in this case is considered to require long - term follow - up through clinical , hormonal , and imaging evaluation owing to its malignant potential .
oncocytoma is a neoplasm consisting of oncocytes that is found in the salivary gland , kidney , and thyroid . 
 adrenocortical oncocytoma is particularly uncommon , and most cases reported are benign and nonfunctioning . here , 
 we report a 20 cm adrenal mass associated with necrosis that was identified as an oncocytic adrenocortical tumor with uncertain malignant potential through histopathological evaluation after its resection .