Renal dysplasia and duplex kidneys

34 children with double ureters (n = 26), bifid ureters (n = 7) or bifid renal pelvis (n = 1) had heminephrectomy, leaving a normal portion of kidney. Patients with ectopic ureteroceles and ectopic ureters had upper pole lesions (18 of 18) whilst the lower pole was more often involved in those with vesico-ureteric reflux (9 of 11). Histological changes of renal dysplasia were present in both upper and lower pole lesions, being generally less severe at the lower pole. These findings suggest that prolonged urinary obstruction plays a major role in the formation of dysplasia in developing kidneys.