Benign renal mesenchymoma in the pediatric age group: a novel pathologic and karyotype entity.

Benign mesenchymal renal tumors are extremely rare in the pediatric age group. We report a case of a benign renal tumor composed of smooth muscle cells, adipose tissue, and areas of cartilaginous differentiation and expressing a 46,XX, t(8;10)(q21;q24) karyotype in a 13-year-old girl. Although some pediatric renal tumors show a degree of heterologous differentiation, none of them exclusively consist of these three well-differentiated mesenchymal components. The unique features of the present case were further confirmed by the karyotype changes, which to our knowledge, have never been described before in a pediatric renal tumor.