RESUMEN
Hydronephrosis is the most common abnormal finding of genitourinary tract detected by fetal ultrasonography. The causes of majority are attributed to ureteropelvic junction(UPJ) obstruction. The remaining are secondary to vesicoureteral reflux, megaureter, or posterior urethral valves. Congenital midureteral stricture is an unusual cause of hydronephrosis. We report a case in a one month old male baby with hydronephrosis(grade V, 20mm in AP diameter). He was diagnosed as a ureteropelvic junction obstruction. A mid ureteral stricture was identified with intraoperative anterograde pyelography. After removal of severely strictured ureter, the dilated proximal end was anastomosed to the spatulated distal ureter by microscope. Pathologic finding was subepithelial fibrosis and segmental inner smooth muscle attenuation. Ureteral stent was removed 2 months after surgery. Degree of hydronephrosis was markedly reduced on the follow up ultrasonography(14mm in AP diameter) 6 months after surgery.