A condition in which a kidney becomes swollen with urine as a result of an obstruction in the urinary tract. Many people with hydronephrosis have a congenital narrowing of the ureter. The obstruction of a ureter may be caused by a stone (see calculus, urinary tract), a kidney tumour, or a blood clot. Occasionally, hydronephrosis is caused by obstruction to the outflow of urine from the bladder by an enlarged prostate gland (see prostate, enlarged). Acute hydronephrosis, with sudden blockage of the ureter, causes severe pain in the loin. Chronic hydronephrosis, in which the obstruction develops slowly, may cause no symptoms until total blockage results in kidney failure. If the blockage can be removed surgically, the kidney is likely to function normally again. Occasionally, however, a kidney is so badly damaged that it requires removal (see nephrectomy).


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