The obstruction and accumulation of urine from the kidneys causes urine retention, which increases the intrarenal pressure, resulting in the gradual expansion of the renal pelvis and calyces, and the atrophy and destruction of the renal parenchyma, collectively known as hydronephrosis. Hydronephrosis is the enlargement of the renal pelvis and calyces accompanied by atrophy of renal tissue due to urinary tract obstruction. If the ducts are narrow or blocked at any part of the urinary tract and the normal function of the nerves and muscles is disturbed, the passage of urine may be hindered, causing urinary flow obstruction. The pressure above the obstruction gradually increases due to poor urine discharge, and the lumen expands, eventually leading to kidney hydrops, dilation, thinning of the renal parenchyma, and renal dysfunction. If there is bilateral obstruction, uremia will occur with serious consequences.