Duplex kidneys are present in the general population at a rate of about 1% and account for 3%–21% of prenatally detected renal anomalies.^1–4 While there are significant data on the natural history and outcomes for prenatal hydronephrosis in simplex kidneys, duplex kidneys tend to be less studied. In part, this could be due to difficulties in collecting a large enough cohort to report meaningful data. Management of duplex kidneys can also be quite variable based on provider preference. Because of this, our regional consortium, the Mid-Atlantic Pediatric Academic Consortium (M-PAC), decided to study duplex kidneys to better understand practice patterns and identify trends in management. Our aim was twofold. This was our first project as a regional consortium; hence, we wanted to work out the logistics for a successful project among multiple institutions. Our other aim, of course, was to have a large, pooled cohort of duplex kidneys to report significant findings that may guide practitioners on their recommendations to patients.

Table 1. Demographic and clinical characteristics

VUR, vesicoureteral reflux.

From 4 academic institutions, we collected data on 242 patients with 271 duplex renal units with hydronephrosis. Primarily, we wanted to evaluate predictive factors for surgical intervention and urinary tract infection (UTI) with duplex kidneys. From our cohort, we learned that 67% of patients underwent surgical intervention for reasons including obstruction (53%), nonfunctioning upper pole (28%) and history of UTI (27%). The most common interventions were incision of ureterocele (27%), heminephrectomy (25%) and ureteral reimplantation (20%; Table 1). No differences were seen in surgical management based on institution. Several factors were predictive of surgical intervention, including hydronephrosis (Society of Fetal Urology and urinary tract dilation grading) and number of prior UTI events (p=0.03/0.001 and p=0.002, respectively). Pathologies including upper pole ureterocele (p=0.02), ectopic ureter (p=0.004) and obstruction (p=0.04) were also significant predictors of surgical intervention (Table 2).

Table 2. Predictors of surgery

UNC, University of North Carolina at Chapel Hill. UTD, urinary tract dilation. UVA, University of Virginia. VCU, Virginia Commonwealth University.

*Met significance.

UTD, urinary tract dilation.

*Met significance.

We found that 30% of the cohort had a UTI. We demonstrated that male gender (p=0.03), circumcision (p=0.01) and antibiotic prophylaxis after the first year of life (p=0.03) were protective against UTI. A large majority of patients in our study were on antibiotic prophylaxis during the first year of life; however, antibiotic prophylaxis did not correlate with decreased UTI risk during the first year of life (Table 3). Roughly half of the UTI events in our cohort occurred during the first year of life. Our data may suggest that the predisposition for UTI is so great in the first year of life with the duplex kidney pathology that antibiotics are ineffective in preventing infection. Pathology was not a significant predictor of UTI risk. We have seen similar trends in UTI risk with simplex kidneys with hydronephrosis where male gender and circumcision were significant factors in decreased UTI rates.^5,6

To my awareness, this study is one of the largest cohorts to date to describe the history, management, and risk factors for surgery and UTI of duplex kidneys. Perhaps the more interesting aspect of the study includes that the rate of surgery for duplex kidneys is fairly high, at almost 70%. UTI rates with duplex kidneys (30%) also appear much higher compared to those quoted for all prenatal hydronephrosis cases, at 8%.⁵ Put together, this may suggest duplex kidneys with hydronephrosis should be treated differently than the routine prenatal hydronephrosis case, where the majority of these can spontaneously improve.

To circle back to one of our aims of the M-PAC project, we learned that consortium work is not easy. In the field of urology, many national and regional groups have been successful: the Society for Fetal Urology Hydronephrosis Registry, National Spina Bifida Patient Registry, Multi-Institutional Bladder Exstrophy Consortium (MIBEC) and the Michigan Urological Surgery Improvement Collaborative (MUSIC), just to name a few. These groups require extreme dedication and time of the collaborators, a regulatory control person, checks and balances for quality data, and strong leadership to pull projects together. We at the M-PAC group hope to be able to continue to deliver more as we finally have our first project under our belts.