Discussion Author(s): Hobart J. Carr
Vesicoureteral reflux (VUR) is defined as the retrograde passage of urine from the bladder into the ureter and often into the collecting system of the kidney. VUR is usually found in infants and young children, who have a very short intravesical course of their distal ureters, such that urine may reflux up this rather incompetent distal ureteral segment. This is called primary VUR, and it tends to run in families. Secondary VUR is that caused by abnormally high bladder pressure (such as may be seen with bladder outlet obstruction; posterior urethral valve is one cause of secondary VUR) or anatomic abnormality near the ureteroveesical junction (such as an adjacent ureterocele in a completely duplicated kidney). Other causes of secondary VUR include urethral obstruction. High hydrostatic pressures in the bladder weaken the ureterovesicular junction (UVJ) musculature and compromise ureteral competence.
Several anatomic relationships must be maintained to ensure UVJ competancy. Optimally the ureter enters the bladder musculature in an oblique angle traversing the bladder wall for an age-related distance, to end in the lateral corner of the trigone. The normal submucosal ureter tunnel measures 0.5cm in the newborn, and has a tunnel to length (i.e. intramural urethral diameter to tunnel length) ratio of 5:1. Simply stated, the larger the uretheral orifice and the shorter the mural course of the ureter the more incompetent the UVJ will be. Without these anatomic relationships the intramural ureter cannot act as a pressure valve with bladder filling. It is important to note that while the intravesical ureter acts like a one-way valve, it is not truly a valve. VUR tends to improve with age due to the growth related increase in tunnel length.
Many anatomic abnormalities exist in the renal and renal collecting systems. Duplex Kidney is defined as the anatomical configuration of two ureters draining one kidney. The 2 separate renal pelves and ureters may remain separate, including 2 separate UVJs in the bladder (this is known as a complete duplication and represents about 1/3 of all duplications) or the ureters may join somewhere inferior to the kidney (there is one UVJ in this type of duplication, known as an incomplete duplication; this type accounts for about 2/3 of all duplications). Duplication is the most common ureteropelvic anomaly with an incidence of 1/160 patients.
Complete duplications are characterized by an upper renal pole moiety that drains thru an unusually long ureter, which often ends in a ureterocele. This ureterocele tends to obstruct the upper pole drainage; hence there may be upper pole hydronephrosis. The lower pole moiety is drained by a normal ureter, although there is a high incidence of VUR into the lower pole. This is thought due to the local anatomic abnormality caused by the upper pole ureterocele adjacent to the lower pole UVJ, which distorts the lower pole UVJ, enabling VUR. Hence, pts with complete duplicatios are at increased risk for UVJ incompetence of the lower pole ureter, which may lead to VUR. VUR is associated with pyelonephritis and renal scarring. Parenchymal scarring is usually caused by urinary tract infection, and not by hydrostatic forces. However with urethral obstruction hydrostatic forces can cause renal damage. Renal damage is usually confined to the upper pole, or the upper and lower pole where there is more than one papilla per calyx. Due to this compound morphology there is a lower threshold of hydrostatic pressure may cause intrarenal reflux than in nonpolar regions. This phenomena is also age dependent and rarely occurs after age 4.
Duplication can be diagnosed via Ultrasound, Voiding Cytourethrogram (VCUG), and radionucleotide studies. Ultrasound is the least invasive of the procedures, but has a lower sensitivity for anatomic aberrations. VCUG has the highest sensitivity for anatomic variations, but offers the highest radiation exposure. Radionucleotide studies paradoxically expose the pt to a lower radiation dose, and are more physiologically revealing for VUR and obstruction, but can be anatomically confusing in complex cases.
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