What is ureteropelvic junction obstruction?
This is a congenital anomaly, in which the renal pelvis does not taper and funnel normally into the ureter, resulting in obstruction at the UPJ. The renal pelvis is located outside of the renal parenchyma (known as an extrarenal pelvis) and is usually large. The appearance of the ureter inserting into the large and dilated renal pelvis is referred to as a “balloon on a string” sign. Congenital UPJ, also known as congenital hydronephrosis, is a very common cause for an abdominal mass in a neonate. The treatment is surgical pyeloplasty and is usually performed laparoscopically.