436 Hwang et al lower pelvis for 4 weeks. Postoperative intravenous pyelog- raphy confirmed that the obstruction had been success- fully relieved and that all renal stones had been success- fully removed (Fig. 4B). DISCUSSION Ureteral duplication is the most common congenital uri- nary tract anomaly. The embryological concept proposed to explain the association of ureteral duplication with ab- normal bifurcation of the ureteral bud is as follows. When the ureteral bud bifurcates shortly after its origin from the mesonephric duct, incomplete ureteral duplication occurs. If the two buds develop close to the normal points of ureteral origin, from the mesonephric duct, a complete duplication results [1]. 　However, ureteral duplication associated with UPJO is rare, and most cases occur in the lower pole of an in- completely duplicated system. This occurs as either a con- genital or an extrinsic compression with aberrant or ac- cessory renal vessels. In addition, high-grade vesicoure- teral reflux may play a casual role in the evolution of some cases of UPJO. It is postulated that dilatation of the collect- ing system as the result of reflux may lead to elongation, tortuosity, kinking, and fibrosis of the ureter. This may be complicated by fixation of the UPJ from periureteral in- flammation, leading to persistent UPJO [2]. 　It is likely that the cause of UPJO in our patients was congenital. During fetal life, the ureter undergoes a con- tinuous process of obstruction and recanalization, which, if incomplete, may produce narrowing and obstruction [3]. In addition, Johnston reported that the fetal ureter may show intraluminal muscular invaginations or folds, which can persist postnatally, and they may produce UPJO [4]. 　Surgical treatment of lower pole UPJO must be planned so that as much functioning renal parenchyma as possible is spared. Dismembered pyeloplasty, end-to-side pyelour- Korean J Urol 2010;51:434-437 FIG. 4. (A) Preoperative retrograde pyelo- graphy showing marked dilatation of the right lower pole moiety suggesting UPJO. (B) The 3-month postoperative IVP showing marked reduction of the hydronephrosis in the lower pole moiety. UPJO: ureteropelvic junction obstruc- tion, IVP: intravenous pyelography. eterostomy, and ureterocalicostomy all are potential surgi- cal treatments; these options should be tailored and modi- fied depending on the intraoperative findings at the time of the procedure [5]. According to Shelfo et al, an ipsilateral pyeloureterostomy (IPU) is a common surgical procedure used to manage ureteral duplication with lower pole UPJO [2]. Open IPU has achieved success rates of 90%. However, open pyeloplasty has several drawbacks, including sub- stantial postoperative pain due to the flank incision and prolonged convalescence. To minimize morbidity, several endoscopic techniques have been developed as alternatives to open surgery, and the endoscopic approach to UPJ has been successful for both the anterograde and retrograde procedures, offering the advantages of shorter operative time, less morbidity, reduction of postoperative analgesic requirements, and shorter hospital stay [6]. 　The minimally invasive techniques that have been de- veloped over the recent past continue to evolve. Since Chandhoke et al described the AcuciseⓇ endopyelotomy in 1993 [7], it has been used for dramatic advances in the field of endourology and has allowed for precise, directed endo- pyelotomy procedures to be performed with high immedi- ate success rates of 87.5% to 100%, the variance of which most likely reflects patient selection [8]. Long-term pa- tency, however, is reportedly 61.5% to 85% after 37 to 60 months of follow-up [9]. The time to failure after endopye- lotomy averages 10 to 20 months, but it is becoming increas- ingly clear that patients treated with endopyelotomy re- quire longer follow-up with renal scintigraphy or intra- venous pyelography. Doo et al reported that the failure rate after endopyelotomy does not nadir until 36 months [6]. 　The main conditions that decrease the success rates of antegrade or retrograde endopyelotomy are the presence of crossing vessel adjacent UPJO, a very large renal pelvis, and a high insertion of the ureter into the renal pelvis [6]. Additional contraindications include extensive periure- teral fibrosis, a bleeding diathesis, a ureter too small to ac-