A case of retroperitoneal immature teratoma with nephroblastic components.

The presence of nephroblastic components is extremely rare in retroperitoneal teratomas. We described an unusual case of right retroperitoneal immature teratoma with nephroblastic components in a 2-month-old Japanese girl. Approximately 15% of tumor was composed of nephroblastic components within immature teratoma components. Although overlap of histopathological findings between teratomas with nephroblastic components and teratoid Wilms tumors, which have heterologous elements in >50% of the tumor, occasionally exist, the most distinct feature of teratoma is the presence of organoid arrangement. The prognosis of retroperitoneal teratomas with nephroblastic components has not yet been established, therefore, additional case studies are needed.