Embryology of a complete uretal duplication and ectopic ureter

Schematic embryologic development of a complete duplex renal collecting system with the formation of 2 ureteral buds. Note that the cranial ureteral bud drains the lower pole of the kidney and the caudal ureter bud drains the upper pole of the kidney. In general, pathology occurs when the caudal ureteral bud inserts in an abnormal distal ectopic location in the bladder (ie, ectopic ureter) or caudal to the bladder causing upper pole ureteral obstruction. When the cranial ureter inserts abnormally, lower pole ureteral reflux can occur.