Congenital ureteropelvic junction obstruction

The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually 20–30 cm (8–12 in) long and around 3–4 mm (0.12–0.16 in) in diameter. [Source: Wikipedia ]

Congenital UPJ obstruction
May Cause
Obstruction of ureter