Response to letter to the editor re how can we measure the renal pelvic anteroposterior diameter in postnatal isolated hydronephrosis?

In their letter to the editor, Arnaud et al. agree with our conclusion about the importance of being consistent in using the same method of APD measurement while evaluating/following up children with postnatal hydronephrosis, as this could significantly affect clinical decision making. For example, if we measure the APD at the inner pelvis and in the subsequent follow up the APD is measured at the extrarenal pelvis, this could lead to a false impression of increasing hydronephrosis when in fact the hydronephrosis may be stable.