Ectopic immature renal tissue presenting as a pedunculated sacral mass in a neonate.

Ectopic immature renal tissue (EIRT) has been reported in a variety of tissues of mesodermal origin, including the dermis of the skin. We report a case of a newborn with a congenital lumbosacral mass with pathologic findings consistent with EIRT. This report highlights the clinical and pathologic considerations of EIRT, including associations with spinal dysraphism, teratoma, and Wilm's tumor.