Nonobstructive dilatation of upper urinary tract may later convert to obstruction.

We report on 5 babies found to have pyelocaliectasis or hydroureteronephrosis antenatally who were evaluated soon after birth because of persistent mild or moderate upper urinary tract dilatation. In each instance, vesicoureteral reflux was absent and the technetium-99m diethylenetriaminepentaacetic acid renal scan revealed good function in the ipsilateral kidney. Renogram curves, after furosemide, did not show an obstructed pattern. Indeed, allowing for the dilatation, the drainage patterns were thought to be normal. In each instance the patient represented or was found on follow-up to have increased dilatation. Renograms were then repeated, using the same radiopharmaceutical and dose of diuretic. An obstructive pattern was seen in each instance. These significant observations demonstrate that nonobstructive hydronephrosis, diagnosed prenatally, may later convert to obstruction at the ureteropelvic junction (UPJ) or in the juxtavesical ureter (UVJ). Thus, careful follow-up, for a period yet to be determined, is desirable in patients in whom the initial postnatal evaluation does not demonstrate obstruction by current criteria.