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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 not a disease in and of itself. Instead, it can be caused by a number of internal and external conditions that affect the kidney and the kidney urinary collecting system. One of the most common causes is a condition is called acute unilateral obstructive uropathy.