How is clinical presentation of UPJ stenosis? How is dX?

Chronic flank pain (especially after drinking increasing renal pressure) Dx: Adults (dx by pain if no imaging) Peds (Intrauterine US, resolves 76% by itself, we see infrarenal obstruction leads to hydronephrosis increase renal pressure causing parenchymal distention (if hydronephrosis with narrow ureter this is UPJ, if dilated ureter this is reflux)) Can be incidental dx