What is Vesicoureteral Reflux (VUR)?
Vesicoureteral reflux (VUR) is the retrograde (backward) flow of urine from the bladder into the ureter and often up to the kidneys, representing an anatomical and/or functional disorder of the ureterovesical junction that primarily affects infants and children. 1
Pathophysiology and Mechanism
Primary VUR results from a defective valve mechanism at the ureterovesical junction, where the ureter enters the bladder. 1 The normal anatomy creates a flap-valve mechanism through a submucosal tunnel, but in VUR this protective mechanism is compromised due to:
- Abnormal location of the ureteral orifice leading to a shortened intravesical ureteral tunnel 2
- Congenital maldevelopment of the ureterovesical junction in most cases 3
- Genetic factors that have been identified through analysis studies 1
Clinical Significance and Consequences
VUR by itself does not cause renal damage postnatally, but when associated with recurrent urinary tract infections (UTIs), it significantly increases the risk of renal scarring and long-term complications. 1
The potentially serious consequences include:
- Renal scarring (reflux nephropathy) - occurs in approximately 15% of children after first UTI episode, with higher rates in those with VUR 4
- Hypertension - develops in 10-20% of children with focal uptake defects on radionuclide scans 1
- End-stage renal disease - VUR may be the second leading cause of renal failure in pediatric populations 5
- Chronic kidney disease - 10-20% of children with renal scarring progress to this outcome 1
Epidemiology and Risk Factors
Among all children presenting with febrile UTIs, boys are more likely to have VUR than girls (29% vs 14%), though febrile UTIs themselves are more common in girls. 1
The prevalence varies by presentation:
- 25-40% of children may be affected according to recent studies 6
- Higher detection rates in children with prenatal hydronephrosis or siblings with VUR 1
- Increased prevalence in children with recurrent UTIs (35-74%) 4
Grading System
VUR is classified into five grades based on the degree of retrograde urine flow and anatomical distortion, which directly impacts management decisions and prognosis. 1
- Grades I-II: Lower-grade reflux with resolution rates of nearly 80% within 4-5 years 1
- Grades III-V: Higher-grade reflux with resolution rates of 30-50% within 4-5 years 1
- Bilateral high-grade reflux: Has particularly low spontaneous resolution rates 1
Associated Conditions
There is a clear co-prevalence between VUR and lower urinary tract dysfunction (LUTD), which may be accompanied by bowel dysfunction. 1
- Bladder and bowel dysfunction (BBD) is common in toilet-trained children presenting with UTI and VUR 1
- BBD increases the risk of febrile UTI and focal uptake defects on radionuclide scans 1
- Among patients with LUTD, the prevalence of focal uptake defects may be as high as 30% 1
Diagnostic Approach
Voiding cystourethrography (VCUG) remains the gold standard for diagnosing VUR, as it allows accurate determination of reflux grade and anatomical assessment. 1
Alternative imaging modalities include:
- Contrast-enhanced voiding urosonography (ceVUS) - reduces radiation exposure 1
- Nuclear cystography - for follow-up assessments 1
- DMSA renal scan - best for visualizing cortical tissue and detecting scarring 1
Natural History
Spontaneous resolution is common in lower-grade VUR but significantly less likely in higher grades. 1
Negative predictive factors for resolution include: