Two main sites of urine flow obstruction in the upper urinary tract are located at the pelviureteric and vesicoureteric junctions, both of which result in urinary tract dilatation. With current antenatal ultrasound screening, most patients are identified before birth, and 10–30% of infants with antenatal hydronephrosis are found to have pelviureteric junction obstruction, and 5–10% vesicoureteric junction obstruction/megaureter. In addition, a megaureter can also be based on urine reflux, even in combination with obstruction, or be a non-refluxing non-obstructed megaureter. In case of obstruction, surgery may be indicated, but identifying cases that need to be operated on is challenging and no good marker to assist in this differentiation is available yet.
