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Content Reviewers:Rishi Desai, MD, MPH
In vesicoureteral reflux, there is some obstruction in that path which causes pressure to build up and a current of urine actually pushes backward from the bladder into the ureters and kidneys.
There are two types of vesicoureteral reflux, or VUR. Primary vesicoureteral reflux is the most common type and happens when a child is born with a defect at the ureterovesical junction, which is the spot where the ureter enters the bladder, which also acts as a valve preventing urine from pushing back from the bladder into the ureter.
Normally about two centimeters of the ureter sticks into the bladder wall, allowing urine to flow into the bladder, but as the bladder fills up and stretches, it also stretches that section of the ureter and presses it against the top of the bladder, causing the ureter to close shut.
If the tube isn’t long enough though, that small piece of the ureter doesn’t stretch very much, and it stays open even when the bladder fills with urine. In that situation, as the bladder pressure builds with more urine, it starts to go back up the ureters.
In secondary vesicoureteral reflux, there’s an obstruction at some point in the urinary tract and it causes an increase in pressure, causing urine to follow the path of least resistance which often means flowing backward into the ureters or kidneys.
Secondary vesicoureteral reflux is most commonly caused by recurrent urinary tract infections, which can cause inflammation in the ureters making them swell up and close.
Another cause that is often diagnosed in babies is called posterior urethral valve disorder, which is when an abnormal membrane develops in the posterior part of the urethra, or the part closest to the bladder, and it prevents urine from easily passing from the bladder into the urethra.
Yet another cause is a flaccid neurogenic bladder, when the bladder is unable to contract to release urine out of the body even when a person is consciously trying to release the urine. This most often results from trauma, disease, or injury to the nervous system.
Vesicoureteral reflux is usually classified by severity - grade I through V, depending on how far urine refluxes back up into the urinary tract.
Grade I, is least severe, and urine only goes up into the ureters.
In grade II, urine fills the entire ureter and the renal pelvis, the center part of the kidney.
In grade III, urine fills and begins to stretch both the ureter and the renal pelvis.
In grade IV, the ureter is so swollen that it begins to get curvy and the renal pelvis and calyces—the urine collection ducts—become moderately swollen and distorted.