During a State-of-the-Art Lecture on Sunday, C.D. Anthony Herndon, MD, FAAP, FACS, examined the association between urinary tract infection (UTI) and prenatal urinary tract dilation (UTD), specifically examining the impact of prophylactic antibiotics for prenatal UTD and the role of imaging in the postnatal period.
Various grading systems are used to describe UTD. The anteroposterior diameter (APD) measurement is the most common system used prenatally, while a combination of APD and the Society for Fetal Urology (SFU) grading system are used postnatally.
“When you have this lack of uniformity, it’s fairly difficult to make meaningful outcomes assessments. Therefore, in 2014 the SFU and the Society for Pediatric Urology adopted the UTD classification system,” said Dr. Herndon, Professor of Surgery/Urology and the Children’s Hospital Foundation of Richmond Endowed Professor of Surgery/Urology at Virginia Commonwealth University, and Chief of Pediatric Urology and Co-Surgeon-in-Chief at the Children’s Hospital of Richmond.
The UTD system is a combination of the SFU grading system and the APD measurement system that focuses on the prenatal and the postnatal periods using objective and subjective measurements.
“Initially, it’s a risk assessment for UTI, deterioration of renal function, risk of surgery, and then an evaluation and management schema based on these risks,” Dr. Herndon said.
Dr. Herndon said it’s important to understand that prenatal kidney dilation is a risk factor for UTI. He cited a Brazilian study that indicated a doubling of risk for each grade of prenatal UTD. A subsequent study demonstrated a similar finding, reporting a threefold increase in the rate of UTI when comparing low-grade to high-grade UTD.
“When we look at the question of whether prophylaxis can prevent these known risks of UTI, unfortunately the data are mixed,” Dr. Herndon said. “Looking at these single-center studies, such as the Brazilian study, there’s a high rate of infection while on prophylaxis, whereas other studies have demonstrated no difference. And then for a select population of secondary reflux, there’s a clear benefit.”
A systematic review of more than 4,000 patients in 2013 demonstrated that low-grade kidney dilation was not impacted by prophylaxis, mainly because of the low incidence of infection. In the same patient group, high-grade kidney dilation had a UTI rate that was reduced by half when prophylactic antibiotics were used.
Another single-center retrospective review of 507 patients with prenatal hydronephrosis reported in 2014 demonstrated a clear trend of benefit with prophylaxis.
“Specifically looking at ureteral dilation, they found that prophylaxis reduced the infection rate fivefold,” Dr. Herndon said. “A more recent systematic review used pool UTI rates and, interestingly, demonstrated no benefit of prophylaxis on the incidence of UTI. They concluded that it is not evidence-based to use prophylactic antibiotics, however there may be a benefit for high-grade kidney dilation.”
Dr. Herndon said there are still several unanswered questions regarding the role of imaging, and specifically the role of lower urinary tract imaging or voiding cystourethrography.
“We know that if we screened everyone who had prenatal kidney dilation, we would detect reflux in about 30 percent of the population. Furthermore, if we looked at the patients who had normal postnatal ultrasounds, reflux would be detected in about 25 percent of this group,” he said. “When we look at reflux, we know that active surveillance is safe and tends to be done in older populations, but the question remains as to whether we can take a similar approach to patients with prenatal UTD who we know have a fairly high potential rate of reflux detection.”