Ectopic immature renal tissue. Report of two cases.

We present two cases of ectopic renal tissue. The first case had a small retroperitoneal nodule near the lower pole of the left kidney, in which the tissue was associated with nervous tissue and differentiating skeletal muscle fibers. The other case presented with a yuxtaepididimal nodule and also contained small groups of ovary hilius like cells. The possibility is raised that ectopic rests like these might be the source of extrarenal Wilms' tumours associated or not with teratomas.