A rare case of bilateral cystic nephroma associated with embryonal rhabdomyosarcoma of the penile urethra.

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.

INTRODUCTION

Cystic nephroma also called multilocular cystic nephroma is an uncommon benign renal neoplasm. Bilateral cystic nephromas are very rare with five cases described in the English literature.[1] Though rhabdomyosarcoma is a very common soft tissue sarcoma that occurs in children, rhabdomyosarcoma affecting the penile urethra is extremely rare.[2] Here, we present a case of bilateral cystic nephroma who subsequently developed embryonal rhabdomyosarcoma of the penile urethra.

CASE REPORT

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. The left flank was normal. 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 underwent bilateral partial nephrectomy in April 2009. Histolopathologic analysis revealed it to be bilateral cystic nephroma. He was well for a period of 2 years when he developed a polypoidal mass protruding from the external urethral meatus. Biopsy revealed it to be an embryonal rhabdomyosarcoma. 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. A dorsal island prepucial flap urethroplasty was done to reconstruct his urethra. The child is doing well more than 2 years after excision of the urethral rhabdomyosarcoma.

DISCUSSION

Bilateral cystic nephromas are extremely rare benign renal neoplasms with five cases described in the English literature. Unilaterality was one of the eight diagnostic criteria proposed by Powell et al.[3] 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[4] 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.

Cystic nephromas mostly are seen in male children <2 years of age. Common modes of presentation include abdominal mass, abdominal pain, and/or hematuria. The most common differential diagnosis is a CPDN and cystic Wilms tumor. 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.[5]

Association of cystic nephroma with embryonic rhabdomyosarcoma has not been noted in the literature. However, an association of bilateral cystic nephroma with pleuropulmonary blastoma has been described[6] 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.[7] Rarely sporadic embryonal rhabdomyosarcoma has been found to be caused by Dicer-1.[89] 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.