Question: hydonephrosis is caused by decreased blood flow to the kidney

Answer: Yes, Hydronephrosis--literally ``water inside the kidney''--refers to distension and dilation of the renal pelvis and calyces, usually caused by urinary retention due to obstruction of the free flow of urine from the kidney. Untreated, it leads to progressive atrophy of the kidney. One or both kidneys may be affected. In cases of hydroureteronephrosis, there is distention of both the ureter and the renal pelvis and calices.