Vesicoureteral reflux (VUR) is the intermittent reversal of normal antegrade flow of urine from the ureter into the bladder. In most affected patients, the important clinical consequence of VUR is the occurrence of recurrent infections that can lead to renal scarring. The major pathophysiological mechanism of scarring is thought to be passage of infected urine from the lower urinary tract into the pelvicaliceal system, with extension into the parenchyma by way of intrarenal reflux through the collecting tubules. When severe, renal scarring can lead to hypertension or renal failure. Severe VUR in the fetus or neonate can lead to renal damage or faulty kidney development. Primary VUR accounts for 15% to 20% of prenatally detected uropathies; this type of reflux occurs with a 5:1 male to female ratio.1
VUR is the abnormal retrograde flow of urine from the bladder into the ureter. It is most often a primary developmental abnormality in which immaturity of the vesicoureteral junction or a short distal ureteric submucosal tunnel in the bladder wall results in a poorly functional valve mechanism. In some instances, there is a specific underlying anatomic abnormality, such as a periureteral diverticulum or ectopic ureteral insertion (Figure 48-1). VUR can also occur as a secondary phenomenon in patients with a bladder outlet obstruction, such as posterior urethral valves. Neuropathic bladder is accompanied by VUR in 15% to 60% of patients.2–4 Dysfunctional voiding plays a role in some instances of primary reflux.5 About three-fourths of girls with reflux have evidence of inhibited bladder contractions.6
Periureteral (Hutch) diverticulum.
A right anterior oblique image from a cystogram shows a large diverticulum (D) arising from the posterolateral aspect of the bladder. Refluxed contrast opacifies the right ureter, which drapes around the diverticulum. There is an abnormal right-angle orientation of the ureter (arrow) at its insertion into the bladder wall.
The valve mechanism at the ureterovesical junction includes both passive and active components. The anatomic characteristics of the ureter and bladder wall provide passive resistance to reflux. The portion of the distal ureter that passes through the bladder wall consists of intramural and submucosal segments. Fixation of the submucosal portion is by muscular segments that extend into the trigone and the bladder base. The intravesicular pressure of the bladder is transmitted to the roof of the submucosal tunnel. When the intravesicular pressure exceeds the intraureteral pressure, the submucosal segment collapses, thereby opposing the retrograde passage of urine from the bladder into the ureter. This anatomic arrangement results in progressive increase in the resistance to reflux with increase in the intravesicular pressure.
Several potential anatomic factors of the ureterovesical junction increase the propensity for reflux. These include an abnormal oblique course of the distal ureter as it courses through ...