Background: The valve function of the ureterovesical-junction (UVJ) is responsible for protection of the low pressure upper urinary tract from the refluxing of urine from the bladder. Controversy about the microanatomy of the human ureterovesical-junction persists.
Methods: Ten (3 male and 7 female) fresh cadaveric bladders (mean age 70 years old) were studied. The bladders were fixed within 24 hours postmortem, frozen, and serially sectioned. Acetyl- and butyryl- (nonspecific) cholinesterase activity were visualised as described by Karnovsky and Roots. The three-dimensional distribution of the different muscle groups participating in the formation of the UVJ was reconstructed.
Results: Three different muscle groups were identified: (1) the detrusor muscle and the deep trigone were mainly acetylcholinesterase-positive, (2) the inner and outer layer of the ureteric muscle were butyrylcholinesterase-positive and merged into a single longitudinal layer at the level of the UVJ and form the superficial trigone distally to the ureteric orifices, and (3) the muscularis mucosae is a discontinuous butyrylcholinesterase-positive layer in the bladder that is absent from the trigone. No evidence of any muscular connection was found between the ureter and bladder musculature.
Conclusions: The anatomy of the UVJ as observed by us suggests the following model of the ureteric peristalsis. The urine bolus arrives in the ureteric lumen at the UVJ level. The ureter can only shorten its length, slides freely in its tunnel, and discharges the urine bolus in the bladder cavity. Ureteric constriction due to the peristalsis and thickening of the contracted portion of the ureter prevents the upstream leakage. Distal spreading of the ureteric "peristalsis" in the superficial trigone increases the submucosal ureteric length and prevents reflux.