[New concept in the treatment of hydronephrosis].

Sixteen cases of pyeloureteral obstruction treated in the period of 24 months are reported. The differential diagnosis, specially with Wilms' tumor must be considered. The low frequency of obstruction secondary to aberrant vessels is also important as etiological cause of pyeloureteral obstruction. This situation contributes to obstruction, but is not the main cause; the same is true with the anomalous implantation of the ureter in the renal pelvis. Within the possible etiological causes, the impairment of function of the pyeloureteral junction must be mentioned as responsible of the dilatation of the renal pelvis. Quite possibly such dysfunction is secondary to an abnormal disposition of the muscle fibers, the same as to the presence of fibrous tissue at the level of said junction. The dynamic evaluation of the ureteropyelic junction was used in two ways, systemic and local, to decide the surgical intervention. The functional evaluations is quite important to avoid unnecessary surgery. Anderson-Hynnes' technique was used to avoid frequent relapses observed when etiological treatment is not done. The correct application of the technique is important to obtain good results.