DefinitionUnilateral hydronephrosis is swelling of one kidney due to a backup of urine.See also: Bilateral hydronephrosisAlternative NamesHydronephrosisCauses, incidence, and risk factorsHydronephrosis is a condition that occurs with a disease. It is not a disease itself. Conditions that are often associated with unilateral hydronephrosis include:Acute unilateral obstructive uropathyChronic unilateral obstructive uropathyVesicoureteric reflux (backflow of urine from bladder to kidney)Nephrolithiasis(kidney stones)Hydronephrosis that occurs without a known cause during pregnancyUnilateral hydronephrosis occurs in approximately 1 in 100 people.SymptomsFlank painAbdominal massNausea and vomitingurinary tract infectionFeverPainful urination (dysuria)Increased urinary frequencyIncreased urinary