The aim of this review is to describe the present status of prenatally diagnosed pyelectasis and hydronephrosis. Ultrasonographic definitions are presented, along with guidelines for the management of urinary tract dilatations. Isolated pyelectasis without caliceal involvement rarely constitutes a pathological situation and does not require any particular diagnostic or therapeutic measures. Obstructive dilatation is characterized by an obstacle to normal urinary flow situated at any level in the urinary tract, with consequent stagnation of urine and dilatation upstream of the obstruction. If the obstruction is not correctly treated it can cause a progressive deterioration of renal function. The presence of ureterectasia plays a crucial role in the diagnostic algorithm and a micturitional cystourethrography is necessary to look for a vesicoureteric reflux (VUR). The significance of urinary tract dilatation is discussed in detail.
Conclusion: In newborns with pyelectasis or hydronephrosis the paediatrician's goal should be to strike the right balance between excessive medical intervention and sufficient intervention for the diagnosis of potentially dangerous conditions.