Paratesticular metastases from congenital retroperitoneal tumor.

A retroperitoneal tumor was removed from a fifteen-day-old infant. Light microscopy revealed a teratoma consisting mainly of immature nervous tissue. Three months later the patient had recurrence and numerous peritoneal metastases showing a histologic pattern similar to that of the primary tumor. Twelve months later there was enlargement of the left testis due to metastases from teratoma infiltrating the tunica vaginalis of the left testis, the epididymis, and the spermatic cord. These metastases consisted of mature neurons and glial cells. The early dissemination of the tumor suggests an intracavitary spread pattern. The tumor maturation in paratesticular structures suggests that mesothelial cells are involved in the differentiation of tumoral germ cells.