Cystic variant of favorable-histology Wilms' tumor presenting with osteolytic metastasis to the ribs.

Cystic neoplasms of the kidney presenting in childhood always present a therapeutic dilemma. Low-risk renal tumors of childhood cover a wide spectrum: cystic nephroma, cystic partially differentiated nephroblastoma and cystic Wilms' tumor. There are difficulties in differentiating these tumors on preoperative imaging. The present case presented such a therapeutic dilemma and was finally diagnosed as a cystic variant of favorable-histology Wilms' tumor with osteolytic metastasis to the ribs. The case is presented in view of its rare presentation and the therapeutic and diagnostic challenges involved.