Vesico-ureteric reflux (VUR), or the retrograde flow of urine from the bladder into the ureter, is an anatomic and functional disorder with potentially serious consequences.
Primary reflux is reflux in an otherwise normally functioning lower urinary tract, whereas secondary reflux is associated with or caused by an obstructed or poorly functioning lower urinary tract, such as that observed with posterior urethral valves or a neurogenic bladder. In both conditions, the ureterovesical junction (UVJ) fails to function as a one-way valve, giving lower urinary tract bacteria access to the normally sterile upper tracts.
Primary reflux is developmental and may manifest as early as in utero or may not be diagnosed till adult life. This occurs due to abnormal implantation of the ureter into the urinary bladder wall. After entering the bladder through the muscular hiatus of the detrusor muscle, the normal distal ureter passes through a submucosal tunnel before opening into the bladder lumen via the ureteral orifice. If the length of the submucosal tunnel or its muscular backing is inadequate, the valve mechanism is incompetent, resulting in reflux.
Beyond the fetal stage, anatomic reflux alone rarely produces renal damage. Ascending infection and pyelonephritis is the essential cause of reflux nephropathy. Large studies have repeatedly demonstrated a close correlation between the frequency of urinary tract infection and severity of reflux nephropathy in patients with vesicoureteral reflux.
Scarring may result from a single episode of pyelonephritis. Most scarring tends to occur at the renal poles, where the anatomy of the renal papillae permits backflow of urine into the collecting ducts. This phenomenon is referred to as intrarenal reflux and gives pathogenic bacteria access to the renal tubules. The subsequent cascade of inflammation, with release of superoxide and other mediators, results in local tissue ischemia and fibrosis. Over time, when enough renal parenchyma is affected, hypertension, renal insufficiency, and renal failure can result.