Ectopic immature renal tissue over the dorsum of lumbar and sacral area in two infants

During reparative surgery for meningomyelocele of the lumbar area, a 7-week-old female infant was found to have a small, well-delineated, subcutaneous, renal blastema. A 3-month-old female infant was found to have immature renal tissue, consisting of glomeruli and tubules, in a soft tissue swelling dorsal to the sacrum. Neither of these patients showed neurologic or renal abnormalities. The second patient has had a disease-free follow-up period of six years. The possible etiology and significance of these benign findings and their relation to the origin of Wilms tumors are discussed.