macroscopically , renal cell carcinomas ( rccs ) generally present as either solid or cystic mass . among cystic rccs , multilocular cystic rcc represents a rare entity that was recognized in 1982 , with a reported incidence of 1 - 4% of all rccs . renal leiomyomas are benign tumors of the kidney originating from smooth muscle cells of the renal capsule , pelvis , calices , or blood vessels . although small renal leiomyomas can be found in about 5% of autopsy specimens , clinical incidence of these lesions is much lower . in this report , we discuss the first case of simultaneous occurrence of a multilocular cystic rcc and a leiomyoma in the same kidney . a 38-year - old man was referred for treatment of a right renal cystic mass found incidentally . physical examination on admission revealed no palpable mass , and laboratory data were negative . computed tomography of the abdomen showed a about 5.4  4.6 cm poorly enhancing cystic mass with enhancing septa in the polar area of the right kidney ( fig . since multilocular cystic rcc could not be excluded , the patient underwent right laparoscopic radical nephrectomy . macroscopically , in the mid pole , a well - circumscribed mass showing a multicystic feature with thin fibrous septa and without expansile tumor nodules was noted . rccs show cystic changes on imaging studies in 4 - 15% of cases [ 4 , 5 ] . since it is often difficult to differentiate cystic rccs from benign cystic lesions , a definite diagnosis can in most cases only be established by histopathologic examination . these include : ( 1 ) intrinsic multiloculated growth ; ( 2 ) intrinsic unilocular growth ; ( 3 ) cystic necrosis , and ( 4 ) origin from the epithelial lining in a pre - existing cyst . because multilocular cystic rcc are more likely to be discovered incidentally , this feature may contribute to their excellent prognosis compared to that of conventional rccs . since the majority of rccs originate from the proximal tubules , the characteristics and/or environment of the proximal tubules are considered to play an important role in the pathogenesis of rcc . recently , imura et al . carried out a detailed immunohistochemical analysis of multilocular cystic rcc cases . they found that in a high proportion of cases , multilocular cystic rcc reacted strongly with the distal nephron markers , but none reacted preferentially with proximal nephron markers . these results illustrate that multilocular cystic rcc originates from the distal nephron , although the precise pathogenesis of cystic formation in multilocular cystic rcc has not been elucidated clearly . renal leiomyomas are benign tumors arising from the mesenchymal ( or connective ) tissue of the kidney . tumors may be subcapsular ( 53% ) , capsular ( 37% ) , or located in the renal pelvis ( 10% ) . a variety of structural patterns have been described at imaging : solid , cystic , and both cystic and solid [ 9 , 10 ] . in 1990 , steiner et al . the first group comprises small cortical or subcortical neoplasms that are usually asymptomatic , less than 2 cm in size , and are often detected incidentally during autopsy or surgery . the second group consists of larger neoplasms that arise from the renal capsule or blood vessels and may be symptomatic . unfortunately , it is almost impossible to clinically distinguish renal leiomyomas from their malignant counterparts . because of their small size ( usually less than 2 cm ) , these smooth muscle - containing tumors are commonly diagnosed during autopsy , and clinical manifestations become apparent only when they grow larger , hemorrhage , or undergo cystic or sarcomatous degeneration . since the finding of primary synchronous renal neoplasms is very uncommon , especially when they have a different histogenesis , up to now , only a few primary , synchronous rccs with different histotypes have been reported . the coexistence of multilocular cystic rcc and leiomyoma has not been documented . this present case is the first report of synchronous renal neoplasms with different histogenesis ( multilocular cystic rcc and leiomyoma ) in a patient without any symptoms . the significance of the relationship between multilocular cystic rccs and leiomyomas is not well understood and needs further exploration .
we present an unusual case of concurrent occurrence of a multilocular cystic renal cell carcinoma and a leiomyoma in the same kidney of a patient with no evident clinical symptoms . 
 a 38-year - old man was found incidentally to have a cystic right renal mass on computed tomography . 
 laparoscopic radical nephrectomy was performed under a preoperative diagnosis of cystic renal cell carcinoma . 
 histology revealed a multilocular cystic renal cell carcinoma and a leiomyoma . 
 this is the first report of this kind of presentation .