9 . Renal duplication

The complex embryogenesis of the kidney and drainage system accounts for the development and frequency of congenital abnormalities. A complete or incomplete double pyelocaliceal system is identified in 0.8% of postmortem examinations. As an incidental finding during intravenous urography, this percentage increases to 3%, of which in 40% of cases, the finding is bilateral. The term “renal duplication” signifies the co-existence of two ureters separately draining the corresponding moieties of the kidney into the urinary bladder, which can present as an ectopic ureter or as an ureterocele. Duplication can be complete or incomplete. The function of both the upper and lower renal poles can be partially or totally affected, with the upper pole being the most commonly involved. Embryologic development can best explain such abnormalities. The primordial ureter anlage of the drainage system emerges as a bud from the caudal part of the mesonephric duct and gradually ascends in a dorso-cranial direction. A single ureteric bud that undergoes bifurcation will induce a variable degree of incomplete duplication of the upper renal segment. Complete duplication is the result of two ureteric buds, leading to the drainage of the kidney by two ureters.