Vesicoureteral reflux (VUR) is a primary congenital malformation found in approximately 1% of newborns and results from an abnormally situated ureteral orifice (too high and lateral) that is loosely attached to a poorly developed trigone. Embryologically the ureteral bud arises from the mesonephric duct more caudally than usual and this results in a short trigone precursor. The trigone is large and poorly muscularised and the ureteral orifice is positioned more laterally with a deficient submucosal tunnel. In series of prenatally detected renal malformations VUR was frequently an associated finding on postnatal evaluation. In 68 cases of prenatally detected pyelectasis, VUR was present in 37%; for hydronephrosis, VUR was present in 35% of 88; for renal abnormalities in general, VUR was present in 38% of 130 cases; for prenatal dilated urinary tract, VUR was present in 21% of 117 and VUR was present in 15% of 39 cases of duplex renal malformations. There is a high incidence of asymptomatic reflux (26-34%) in siblings of children with known reflux, and multifactorial inheritance seems most likely. However, in some families it appears to be autosomal dominant or sex-linked. Spontaneous resolution of prenatal VUR can occur neonatally but VUR is thought to be responsible for approximately 10% of cases of end stage renal failure in young adults.
VUR should be suspected prenatally (but usually diagnosed postnatally) as a possible cause for renal pelvic dilatation or hydronephrosis. It is an associated contralateral finding in unilateral renal agenesis or nonfunctioning kidney and multicystic kidney. It is also associated with other renal malformations and frequently involves the lower pole ureter in ureteral duplication. It can occur in association with or secondary to a dilated obstructed urinary tract. In cases of megacystis, percutaneous vesicoinfusion at the time of vesicocentesis has been used to document reflux. Further evaluation of this method is necessary.
Renal pelvic dilatation and hydronephrosis may be the result of an obstructive non refluxing lesion (UPJ obstruction, UVJ obstruction, PUV etc). However, obstructive lesions often show progressive changes. Oligohydramnios in the presence of an enlarged bladder is an indicator of urethral obstruction. However, normal or increased amniotic fluid volume can coexist with urethral obstruction if other organ system malformations (e.g. gastrointestinal) are present. Megaureter may or may not be associated with reflux.
Renal pelvic dilatation, unilateral or bilateral
Hydronephrosis, hydroureter, megacystis may be present
Hydronephrosis usually mild and nonprogressive, occasionally severe and can be intermittent
Renal duplication and/or ureterocele may be associated
Contralateral renal agenesis or malfunctioning kidneys (VUR 37%) or multicystic kidney (VUR 15%) may be present
Amniotic fluid usually normal unless associated with obstruction
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