DefinitionBilateral hydronephrosis is the enlargement (distention) of the urine collecting structures and pelvis of both kidneys. Bilateral means both sides.See also: Unilateral hydronephrosisAlternative NamesHydronephrosis - bilateralCauses, incidence, and risk factorsBilateral hydronephrosis occurs when urine is unable to drain from the kidney down the ureters into the bladder. Hydronephrosis is not itself a disease, but rather a physical result of whatever disease is keeping urine from draining out of the kidneys, ureters, and bladder.Disorders associated with bilateral hydronephrosis include:Acute bilateral obstructive uropathyBladder outlet obstructionChronic bilateral obstructive uropathyNeurogenic bladderPosterior ureteral valvesPrune belly syndromeUteropelvic junction obstructionVe