The incidence and importance of renal duplication.

The excretory urograms performed on 1716 children and 3480 adults have been examined to find the incidence and complications of renal duplication. Ninety-five patients with duplication were found, unilateral in 79 and bilateral in 16 patients. It was equally common on each side and twice as common in females as in males. Non-duplex kidneys had a mean of 9.4 calyces and duplex kidneys had a mean 3.7 upper and 7-6 calyces in lower moieties. In patients without renal disease and with unilateral duplication the two kidneys were equal in size in 39%, and the duplex was smaller in 10%. Twenty-seven per cent of the duplex kidneys examined showed evidence of disease compared to 3% of the non-duplex kidneys-a significant difference (P less than 0-001). Saddle reflux is the only abnormality unique to duplication and was seen in one patient. Extravesical ectopic ureter and ureterocoeles are known to be associated with renal duplication, but in this series ureterocoeles were found only on the non-duplex side. The duplex kidney in children is more susceptible to reflux than is the non-duplex kidney, and this leads to both ureteric and pelvi-calyceal dilation, and to chronic pyelonephritis in the duplex side in those children who develop urinary tract infections. Chronic pyelonephritis was found in 22% of patients under 15, significantly more often than in adults (P less than 0-001), although the incidence of duplication was unchanged. It is concluded that there is no real increase in the number of children with duplex kidneys having urinary tract infections, and the vast majority of duplex kidneys do not become diseased.