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Freebase(0.00 / 0 votes)Rate this definition: Hydronephrosis â literally water inside the kidney â refers to distension and dilation of the renal pelvis and calyces, usually caused by obstruction of the free flow of urine from the kidney. Untreated, it leads to progressive atrophy of the kidney.
Hydronephrosis is usually caused by a blockage in the urinary tract or something disrupting the normal workings of the urinary tract.The urinary tract is made up of the kidneys, the bladder, the ureters (the tubes that run from the kidney to the bladder) and the urethra (the tube that carries urine out of the body). blockage or problem in the urinary tract can mean urine is unable to drain from the kidneys or is able to flow the wrong way up into the kidneys. This can lead to a build-up of urine in the kidneys, causing them to become stretched and swollen.