a 37-year - old woman was referred to our institution with a right renal mass that was incidentally found during an evaluation for hypertension . abdominal computerized tomography revealed a well - demarcated non - enhanced cystic mass at the lower pole of the patient 's right kidney ( fig . the patient had no history of tuberous sclerosis and has not shown any evidence of recurrence at 12 months after surgery . the kidney measured 115.53.5 cm and weighed 146 g. located in the cortex of the lower pole of the right kidney , the tumor measured 3.5 cm in size , was well - circumscribed , appeared as a black pigmented mass with cystic changes and was filled with blood clots and chocolate - like fluid ( fig . the tumor was well demarcated from the renal parenchyma and was partially encapsulated by a thick fibrous capsule ( fig . the solid portion of tumor was composed of sheets or nests of large polygonal tumor cells . these cells had round to oval nuclei with prominent nucleoli , and eosinophilic or clear cytoplasm . also , they contained brown pigment in their cytoplasm , which reacted strongly with fontana - masson stain ( fig . 3 ) , but negative for other melanocytic markers ( s-100 protein and melan a ) , cytokeratin ( ae1/ae3 ) , epithelial membrane antigen , cd10 , vimentin , smooth muscle actin , cd68 , c - kit and neuroendocrine markers ( cd56 , synaptophysin , and chromogranin ) . also , the ki-67 labeling index was low ( < 1% ) . the kidney measured 115.53.5 cm and weighed 146 g. located in the cortex of the lower pole of the right kidney , the tumor measured 3.5 cm in size , was well - circumscribed , appeared as a black pigmented mass with cystic changes and was filled with blood clots and chocolate - like fluid ( fig . the tumor was well demarcated from the renal parenchyma and was partially encapsulated by a thick fibrous capsule ( fig . the solid portion of tumor was composed of sheets or nests of large polygonal tumor cells . these cells had round to oval nuclei with prominent nucleoli , and eosinophilic or clear cytoplasm . also , they contained brown pigment in their cytoplasm , which reacted strongly with fontana - masson stain ( fig . 3 ) , but negative for other melanocytic markers ( s-100 protein and melan a ) , cytokeratin ( ae1/ae3 ) , epithelial membrane antigen , cd10 , vimentin , smooth muscle actin , cd68 , c - kit and neuroendocrine markers ( cd56 , synaptophysin , and chromogranin ) . the kidney measured 115.53.5 cm and weighed 146 g. located in the cortex of the lower pole of the right kidney , the tumor measured 3.5 cm in size , was well - circumscribed , appeared as a black pigmented mass with cystic changes and was filled with blood clots and chocolate - like fluid ( fig . the tumor was well demarcated from the renal parenchyma and was partially encapsulated by a thick fibrous capsule ( fig . the solid portion of tumor was composed of sheets or nests of large polygonal tumor cells . these cells had round to oval nuclei with prominent nucleoli , and eosinophilic or clear cytoplasm . also , they contained brown pigment in their cytoplasm , which reacted strongly with fontana - masson stain ( fig . 3 ) , but negative for other melanocytic markers ( s-100 protein and melan a ) , cytokeratin ( ae1/ae3 ) , epithelial membrane antigen , cd10 , vimentin , smooth muscle actin , cd68 , c - kit and neuroendocrine markers ( cd56 , synaptophysin , and chromogranin ) . in contrast to reports of epithelioid angiomyolipoma , the black cut - surface due to heavy melanin pigmentation was a distinguishing feature in this case ; the differential diagnoses considered for this case included malignant melanoma , pigmented clear cell renal cell carcinoma , and composite paraganglioma . malignant melanoma in the kidneys is usually located in the renal pelvis and in cases of metastatic lesions , multifocal metastasis is common.7 however , our patient did not exhibit a primary lesion and the tumor was located in the cortex . in addition , the tumor cells did not express other melanocytic markers such as s-100 protein and melan a. accordingly , the clinical features and immunoprofile did not indicate the presence of malignant melanoma . furthermore , we were able to differentiate the pecoma in our case from pigmented clear cell renal cell carcinoma according to its immunoprofile . conventional renal cell carcinoma distinctively expresses epithelial markers , such as cytokeratin or epithelial membrane antigen and others , cd10 , and vimentin . similar to the present case , paragangliomas are composed of sheets or nests of large polygonal cells with intervening fibrovascular septa . moreover , this type of tumor shares many similar cytomorphological features with pecoma . however , paragangliomas express neuroendocrine markers , which were not observed in the present case . in the literature , only a few heavily pigmented pecoma of the kidney have been reported ( table 1).3 - 6,8 - 11 interestingly , among ten reported cases , including our case , eight cases occurred in women , ranging in age from 12 to 73 years old . one of the cases that occurred in a male patient presented as a component of a triple synchronous neoplasm in one kidney , of which the other two components were clear cell and chromophobe renal cell carcinomas.12 unlike typical epithelioid angiomyolipomas that are frequently associated with tuberous sclerosis , only one pigmented pecoma patient exhibited tuberous sclerosis.13 in the literature , tumors ranged in size from 2.5 to 11 cm . among seven cases which the tumor was located in the kidneys , five cases were located in the lower pole of the kidneys . all of the tumors were composed of sheets of eosinophilic to clear epithelioid cells , and they distinctively exhibited immunohistochemical reaction with hmb-45 . although long - term follow - up data have not yet been established , three patients showed metastasis and three patients , including two with recurrence , died of the disease . according to a study by brimo et al.,14 among 40 cases of renal epithelioid angiomyolipoma their study also devised a predictive model comprising four atypical features of epithelioid angiomyolipoma including the proportion of atypical epithelioid cells , mitotic figures , atypical mitotic figures , and necrosis.14 in the present case , mitotic figures were rare and nuclear pleomorphism was mild . moreover , necrosis was not found . recently , nese et al.15 analyzed 41 cases of pure epithelioid pecoma of the kidney , and found five adverse prognostic parameters associated with disease progression ( recurrence , metastasis , or death due to the disease ) , which included an associated tuberous sclerosis complex or concurrent angiomyolipoma , necrosis , tumor size>7 cm , extrarenal extension and/or renal vein involvement , and carcinoma - like growth pattern characterized by large cells arranged as a cohesive nest , broad alveoli , and compartmentalized sheets separated by thin vascular - rich septae . among them , only a carcinoma - like growth pattern and extrarenal extension and/or renal vein involvement were independent parameters associated with unfavorable outcomes.15 in this regard , the histologic findings of our case , which included sheets or nests of large polygonal tumor cells with delicate fibrovascular septa between tumor cell nests , could be characterized as demonstrating a carcinoma - like growth pattern and may suggest an increased risk of disease progression . although the patient has not shown any evidence of recurrence at 12 months after surgery , long - term follow - up is warranted . in summary , we report a rare case of heavily pigmented pecoma presented as a solitary mass in the kidney . when a pigmented tumor with epithelioid cytologic features is encountered in the kidney , differential diagnosis thereof should be thoughtfully undertaken , and immunohistochemical staining with hmb-45 and other melanocytic markers or epithelial markers would be helpful in differentiating pecoma from malignant melanoma or pigmented renal cell carcinoma .
heavily pigmented perivascular epithelioid cell tumors ( pecoma ) are rare , only eight cases of which have been reported . 
 unlike typical epithelioid angiomyolipoma , most of these tumors have been encountered in female patients without tuberous sclerosis . 
 the long - term prognosis thereof is undetermined . 
 cytological similarity and heavy melanin pigment make it difficult for pigmented pecoma to be differentiated from pigmented clear cell renal cell carcinoma or malignant melanoma . 
 the immunoprofile of tumor cells , such as human melanoma black-45 expression , as well as the absence or presence of other melanocytic or epithelial markers , are helpful in determining a differential diagnosis . here 
 we report a case of heavily pigmented pecoma of the right kidney and review the literature describing this tumor . in this case , the immunoprofile and clinical features corresponded well to those described in the literature . since the prognosis of such disease has not yet been established , close follow - up of this patient was recommended .