Requirements for accurately diagnosing chronic partial upper urinary tract obstruction in children with hydronephrosis.

Successful management of hydronephrosis in the newborn requires early accurate diagnosis to identify or exclude ureteropelvic junction obstruction. However, the presence of hydronephrosis does not define obstruction and displays unique behavior in the newborn. The hydronephrotic kidney usually has nearly normal differential renal function at birth, has not been subjected to progressive dilation and except for pelvocaliectasis does not often show signs of high-grade obstruction. Furthermore, severe hydronephrosis resolves spontaneously in more than 65% of newborns with differential renal function stable or improving. The diagnosis of obstruction in newborn hydronephrosis is challenging because the currently available diagnostic tests, ultrasonography and diuretic renography have demonstrated inaccuracy in diagnosing obstruction and predicting which hydronephrotic kidney will undergo deterioration if untreated. Accurate diagnosis of obstruction is possible but it requires an understanding of the uniqueness of both the pathophysiology of obstruction and the biology of the kidney and renal collecting system in this age group. We examine here the requirements for making an accurate diagnosis of obstruction in the young child with hydronephrosis.