Cystic partially differentiated nephroblastoma (CPDN) is a rare pediatric renal tumor composed of multiple cystic spaces divided by septa containing immature nephrogenic elements. The presence of expansile solid areas in the septa of such a lesion indicates an alternative diagnosis of Wilms tumor (WT). We present a unique case of CPDN associated with grossly visible polypoid proliferations, which histologically correspond to botryoid growth of intralobar nephrogenic rests. Correct pathological diagnosis of CPDN and its differentiation from cystic WT can be challenging, but is critical, because of the distinct treatment approaches and prognoses of these entities, since CPDN is a low-risk tumor not requiring further postoperative therapy.
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