[Histological findings of the ureteropelvic junction in congenital hydronephrosis (author's transl)].

Histological investigation of ureteropelvic junction (UPJ) specimens of 21 patients with congenital hydronephrosis revealed in 7 instances pathological changes, which might be responsible for the obstruction. In 15 cases a significant increase of collagenous tissue within the UPJ, along with a relative deficiency of monocytes was noted. Each of the smooth muscle fibers was surrounded by fibrous tissue, which caused interruption of the "nexus" function and therefore loss of muscle contractions. The inability of normal muscle contractions within the UPJ might be a contributing factor to the pathogenesis of congenital hydronephrosis.