bilateral cystic nephromas are very rare with five cases described in the english literature . though rhabdomyosarcoma is a very common soft tissue sarcoma that occurs in children , rhabdomyosarcoma affecting the penile urethra is extremely rare . here , we present a case of bilateral cystic nephroma who subsequently developed embryonal rhabdomyosarcoma of the penile urethra . a 4-month - old male child presented in 2009 with the right flank mass that was progressively increasing for 2 months . examination revealed a soft , cystic , mobile , nontender , bimanually palpable and ballotable mass in the right lumbar region . imaging ( ultrasonography and computed tomography ) revealed two well - circumscribed multilocular noncommunicating cystic lesions , the larger one arising from the middle and lower pole of the right kidney , and a smaller one from the upper pole of the left kidney . a diagnosis of bilateral cystic nephroma / bilateral cystic partially differentiated nephroblastoma ( cpdn ) was made on the basis of the imaging . he was well for a period of 2 years when he developed a polypoidal mass protruding from the external urethral meatus . he was categorized as stage 1 rms and complete excision of the penile urethra with eight cycles of the postoperative vincristine , actinomycin - d , and ifosfamide was administered . the child is doing well more than 2 years after excision of the urethral rhabdomyosarcoma . bilateral cystic nephromas are extremely rare benign renal neoplasms with five cases described in the english literature . for the diagnosis of cystic nephroma , the other seven being solitary lesion ; multilocular lesion ; noncommunication of the cyst with the renal pelvis ; noncommunication of the cysts with each other ; loculi lined by epithelium ; intralocular septa devoid of renal parenchyma ; and if residual renal tissue was present , it should be normal . these criteria were modified by boggs and kimmelstiel to include the presence of immature renal tissue in the intervening septa . more recently elimination of unilaterality from the diagnostic criteria has been proposed in consideration of the increasing numbers of bilateral cystic nephroma . cpdn is a lesion with low malignant potential , which is radiologically and grossly indistinguishable from cystic nephroma . differentiation between the two is based on histological confirmation of the presence of blastemal cells within the septa . differentiation from cystic wilms is based on the absence of solid elements other than septa in cystic nephroma . however , an association of bilateral cystic nephroma with pleuropulmonary blastoma has been described with dicer-1 mutation being implicated as the cause . germline mutation in dicer-1 causes a variety of cancers , the most common being pleuropulmonary blastoma , cystic nephroma , and ovarian sertoli - leydig cell tumors . dicer-1 gene expresses a protein that plays an important role in regulating the activity of other genes by aiding the formation of micro rna . since bilateral cystic nephroma and urethral rhabdomyosarcoma are extremely rare lesions , their occurrence in the same child is unlikely to be coincidental . dicer-1 mutation could be the cause of this association , but the genetic analysis could not be done due to financial reasons .
bilateral cystic nephroma is an extremely rare benign renal neoplasm . here 
 we present a case of bilateral cystic nephroma in a four month old boy who subsequently developed embryonal rhabdomyosarcoma of the urethra . 
 both tumors were successfully treated . to our knowledge 
 this is the first reported case of this association which could be related to dicer-1 mutation .