Immature renal tissue in colonic wall of patient with caudal regression syndrome.

We report an incidental microscopic finding of ectopic renal tissue in a newborn with multiple congenital anomalies. The ectopic renal tissue was located in the wall of the distal blind end of the colon. The tissue was composed of undifferentiated renal blastema with primitive and well-formed glomeruli and tubules. The potential for malignant transformation of this lesion into extrarenal Wilms' tumor is not known.