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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.
A hydronephrosis is when the the pelvis of the kidney and eventually even the calyx becomes dilated as the fluid accumulates within it. Hydroureter is a dilation of the ureter as the urine accumulates within it and causes distension. A hydroureter is unlikely to occur with a blockage at the ureteropelvic junction â this is where the kidney (renal pelvis) and ureter meet.