Under normal circumstances, the ureterovesical junction allows urine to enter the bladder but prevents urine from regurgitating into the ureter, particularly at the time of voiding. In this way, the kidney is protected from high pressure in the bladder and from contamination by infected vesical urine. When this valve is incompetent, the chance for development of urinary infection is significantly enhanced, and pyelonephritis may occur. In significant cases especially in children, pyelonephritis—acute, chronic, or healed—is secondary to vesicoureteral reflux (VUR).
An understanding of the causes of VUR requires knowledge of the anatomy of the ureterovesical valve. Anatomic studies performed by Hutch (1972) and by Tanagho and Pugh (1963) (Figure 13–1) are incorporated into the following discussion.
Normal ureterotrigonal complex. A: Side view of ureterovesical junction. Waldeyer's muscular sheath invests the juxtavesical ureter and continues downward as the deep trigone, which extends to the bladder neck. The ureteral musculature becomes the superficial trigone, which extends to the verumontanum in the male and stops just short of the external meatus in the female. B: Waldeyer's sheath is connected by a few fibers to the detrusor muscle in the ureteral hiatus. This muscular sheath, inferior to the ureteral orifices, becomes the deep trigone. The musculature of the ureters continues downward as the superficial trigone. (Redrawn and modified, with permission, from Tanagho EA, Pugh RCB: The anatomy and function of the ureterovesical junction. Br J Urol 1963;35:151.)
The mesodermal component, which arises from the Wolffian duct, is made up of two parts that are innervated by the sympathetic nervous system:
The Ureter and the Superficial Trigone
The smooth musculature of the renal calyces, pelvis, and extravesical ureter is composed of helically oriented fibers that allow for peristaltic activity. As these fibers approach the vesical wall, they are reoriented into the longitudinal plane. The ureter passes obliquely through the vesical wall; the intravesical ureteral segment is thus composed of longitudinal muscle fibers only and therefore cannot undergo peristalsis. As these smooth-muscle fibers approach the ureteral orifice, those that form the roof of the ureter swing to either side to join those that form its floor. They then spread out and join equivalent muscle bundles from the other ureter and also continue caudally, thus forming the superficial trigone. The trigone passes over the neck of the bladder, ending at the verumontanum in the male and just inside the external urethral meatus in the female. Thus, the ureterotrigonal complex is one structure. Above the ureteral orifice, it is tubular; below that point, it is flat.
Waldeyer's Sheath and the Deep Trigone
Beginning at a point about 2–3 cm above the bladder, an external layer of longitudinal smooth muscle surrounds the ureter. This muscular sheath passes through the vesical wall, ...