The duplicated collecting system of the urinary tract: embryology, imaging appearances and clinical considerations

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.

Voiding urosonography (VUS) encompasses examination of the urinary tract with intravesical administration of US contrast agent (UCA) for diagnosis of vesicoureteric reflux (VUR). The real breakthrough for US examination of VUR came with the availability of stabilized UCAs in the mid-1990s. This article presents a comprehensive review of various procedural aspects of VUS. Different US modalities are available for detecting the echogenic microbubbles: fundamental mode, colour Doppler US, harmonic imaging and dedicated contrast imaging with multiple display options. The reflux is graded (1 to 5) in a similar manner to the system used in voiding cystourethrography (VCUG). The most commonly used UCA for VUS, Levovist, is galactose-based and contains air-filled microbubbles. The recommended concentration is 300 mg/ml at a dose of 5–10%, or less than 5%, of the bladder filling volume when using fundamental or harmonic imaging modes, respectively. There are preliminary reports of VUS using a second-generation UCA, SonoVue. Here the UCA volume is less than 1% of the bladder filling volume. There is no specific contraindication to intravesical administration of UCA. The safety profile of intravesical Levovist is very high with no reports of side effects over a decade of use in VUS.

Studies comparing voiding urosonography (VUS) with voiding cystourethrography (VCUG) and direct radionuclide cystography (DRNC) were analyzed and detailed tables demonstrating the diagnostic values and grading of vesicoureteric reflux (VUR) are presented. Comparative studies of DRNC were too few and did not allow definite conclusions. Using VCUG as the reference, the results of VUS were as follows: sensitivity 57-100%, specificity 85-100%, positive/negative predictive values 58-100%/87-100%, respectively, and diagnostic accuracy 78-96%. With the exception of two studies the diagnostic accuracy reported was 90% and above. In 19% of pelviureteric units (PUUs) the diagnosis was made only by VUS and in 10% only by VCUG. Thus in 9% of PUUs more refluxes were detected using VUS. In 73.6% the reflux grades were concordant in VUS and VCUG. Reflux grade was found to be higher with VUS than with VCUG in 19.6% of PUUs. In 71.2% of PUUs with grade I reflux on VCUG, the reflux was found to be grade II and higher on VUS. The common selection criteria for VUS as the primary examination for VUR currently include (a) follow-up studies, (b) first examination for VUR in girls, and (c) screening high-risk patients.