Pediatric Ureteropelvic Junction Obstruction Treatment & Management
- Author: John M Gatti, MD; Chief Editor: Marc Cendron, MD more...
Upon diagnosis of a ureteropelvic junction (UPJ) obstruction, prompt intervention is appropriate to prevent or minimize renal damage. First, prophylactic antibiotic therapy is warranted in cases of moderate-to-severe dilatations because any urinary tract infection (UTI), especially in the neonatal period, dramatically increases the chance of fibrosis and parenchymal damage.
The authors recommend the following indications for surgical interventions:
Ipsilateral UPJ obstruction with less than 40% of differential renal function (DRF) on diuretic renography
Bilateral severe UPJ obstruction with renal parenchymal atrophy
Obstructive pattern on diuretic renography with abdominal mass, urosepsis, or other symptoms (eg, cyclic flank pain, vomiting)
Recurrent UTI under antibiotic prophylaxis
Patients with renal function better than 40% are monitored with repeat renal scans at 3- to 6-month and 12-month intervals, and surgery is performed only if a clear deterioration in renal function is present.
In cases where DRF is less than 10%, some recommend the insertion of a nephrostomy tube to determine whether return of function will be sufficient; however, the disadvantages of nephrostomy are the inevitable bacteriuria and the practical difficulty of maintaining a tube in an infant. Performing nephrectomy is rare in UPJ obstruction; however, if the differential function is less than 10%, nephrectomy can be considered to relieve recurrent infection or renal hypertension.
Conditions that preclude anesthesia are contraindications for surgical therapy. In addition, other common surgical contraindications (eg, coagulation abnormalities) should be ruled out before definitive surgical treatment is performed.
It is worth noting that the widespread use of modern imaging techniques has not led to an increase in the number of pyeloplasties performed. In a multi-institutional study investigating the total number of pyeloplasties performed in a well-defined region, the total number of operations was found to have remained constant since the late 1970s. The number of pyeloplasties conducted in children aged 1-6 years increased, whereas the number of pyeloplasties in children aged 7-12 years decreased; yet the total number performed per year remained the same.
In other words, the degree of hydronephrosis, impaired isotope washout, or even reduced differential renal function neither helps to define significant obstruction nor predicts deterioration.
The timing of surgical correction of hydronephrosis suggestive of UPJ obstruction in newborns is highly controversial. Those who support delayed management contend that for most newborns with relatively preserved DRF (>35% of DRF), hydronephrosis is a relatively benign disease without proof of progression. Renal function does not deteriorate; thus, immediate surgery is not necessary.
In a study by Koff and Campbell, approximately 81 of 104 patients were followed for 5 years; seven (7%) of those patients ultimately required pyeloplasty, and, even in these cases, pyeloplasty successfully restored the differential renal function to predeterioration levels.
Researchers also observed that in 15 of 16 patients with severe hydronephrosis (grade 4 hydronephrosis according to the Society for Fetal Urology [SFU] Guidelines) associated with a differential renal function of less than 40%, spontaneous improvement occurred in the initial obstructive patterns on renal scans, and for six of the patients, it became unobstructed. Similar results were observed with ultrasonography; hydronephrosis disappeared in six kidneys and improved in another six.
Thus, the difficulty in determining the indication of surgical management is twofold. First, results from ultrasonography and diuretic renography to assess hydronephrosis can be inaccurate and sometimes misleading. Second, some significant cases of hydronephrosis that are discovered by these modalities may not be obstructive at all.
Therefore, Koff redefined obstruction as "any restriction to urinary outflow, which if untreated will injure the kidney" to provide a clinically useful guideline; Koff recommended that most unilateral hydronephrosis actually is unobstructed and, thus, benign, which can be observed safely nonoperatively.
The role of antibiotic therapy for hydronephrosis remains debatable. Many have advocated using antibiotics for higher grades (SFU 3 or 4) of hydronephrosis. Current data, however, suggest that prophylaxis is less supported in cases of isolated hydronephrosis but remains supported in the presence of hydroureteronephrosis.
In the early 1980s, ultrasonographic identification of obstruction in many infants resulted in a dramatic increase in the number of neonatal pyeloplasties performed. Initially, newborn pyeloplasty had a reported reoperation rate of 20%, which improved with experience. The relative ease and safety of newborn pyeloplasty stimulated discussion about the necessity of intervention.
Physiologically, the newborn kidney is quite different from the adult kidney, particularly in its response to stimulation by the renin-angiotensin system. Renal function could be preserved by relieving the obstruction, achieving maximal benefit in the youngest of kidneys. Because renal failure caused by obstructive uropathy is a definite clinical dilemma, it may be appropriate to perform immediate pyeloplasty at the time of presentation, even in the asymptomatic infant.
Unilateral pyeloplasty not only improves hydronephrosis but also significantly increases creatinine clearance (as calculated by the Schwartz formula) and somatic growth. The implication is that unilateral obstruction has negative effects on renal function and on somatic growth.
The most compelling supporting data on early surgical correction come from animal experiments suggesting that prolonged partial ureteral obstruction is deleterious to the newborn kidney and can be reversed by early relief of the obstruction. Spontaneous resolution of hydronephrosis may not be as benign as was proposed by Koff and Campbell ; 15-33% of patients with asymptomatic neonatal hydronephrosis show progressive ipsilateral renal deterioration, and about one half of them never regain the lost function after vpyeloplasty.
Two well-designed longitudinal studies provided valuable information against initial observation and delayed management. In a study by Ransley et al, in which 100 infants with DRF of hydronephrotic kidney higher than 40% were followed nonoperatively, 23 eventually underwent pyeloplasty during 6 years of follow-up. Of these patients, five completely recovered renal function, four partially recovered, three had no change, and one further deteriorated after pyeloplasty. Thus, eight of 100 initially well-functioning kidneys sustained permanent deterioration with this approach.
Similar results were observed in a study by Cartwright and Duckett, which included results from 39 infants with a cutoff value of 35% of DRF. Six patients (15%) underwent pyeloplasty because of decreasing renal function, urinary tract infection (UTI), or pain.
The observation approach allows the physician to avoid risks associated with surgery and anesthesia, but there is a definite percentage of patients who sustain irreversible renal damage that could have been prevented by early pyeloplasty. Furthermore, after a short learning period, the pyeloplasty in infants is not demanding and is associated with little perioperative morbidity.
Upon diagnosis of a UPJ obstruction, prompt intervention is appropriate to prevent or minimize renal damage. Whether prophylactic antibiotic therapy is necessary is debated; however, it may be considered.
Although there is no definitive factor that mandates intervention, the following may be considered as indications for surgical intervention:
Ipsilateral UPJ obstruction with less than 40% of DRF on diuretic renography
Bilateral severe UPJ obstruction with renal parenchymal atrophy
Obstructive pattern on diuretic renography with abdominal mass, urosepsis, or other symptoms (eg, cyclic flank pain, vomiting)
Recurrent UTI under antibiotic prophylaxis
Worsening hydronephrosis on serial ultrasonography
Patients with hydronephrosis that does not warrant immediate intervention can be monitored with repeat ultrasonography at 3- to 6-month intervals early in life. Serial renal scans can be considered, but the value of this study should be balanced against the risk of radiation exposure. In cases where DRF is less than 10%, some recommend the insertion of a nephrostomy tube to determine whether return of function will be sufficient; however, the disadvantages of nephrostomy are the inevitable bacteriuria and the practical difficulty of maintaining a tube in an infant.
Performing nephrectomy is rare in UPJ obstruction; however, if the differential function is less than 10%, nephrectomy can be considered to relieve recurrent infection or renal hypertension.
It is important to recognize that none of the above surgical indications are absolute. There can be a role for observation of a patient with less than 40% DRF; similarly, there can be cases where nephrectomy is reasonable even if DRF is greater than 10%. All factors must be individualized and interpreted in the context of any other pertinent medical issues that may be present.
Conventional open techniques
The technique of complete ureteral transection followed by reanastomosis to the renal pelvis was first described in the management of a retrocaval ureter, but it was easily adapted for reconstructing the UPJ obstruction. Many different approaches have been tried, such as lumbotomy, flank, or anterior extraperitoneal incision, but the essence of repair consists of excision of the narrowed segment, spatulation, and anastomosis to the most dependent portion of the renal pelvis.
In 1936, Foley introduced the YV-plasty for the correction of UPJ obstruction with high ureteral insertion; it is also applicable to most cases of horseshoe kidney. However, this technique could not be applied in conjunction with transposition of a lower-pole vessel, nor any reduction in pelvis size. Culp and Deweerd designed a spiral flap in the dilated pelvic tissue and used it to repair the defect of the UPJ.
However, the Anderson-Hynes dismembered pyeloplasty, which consists of excision of the narrowed segment, spatulation, and anastomosis to the most dependent portion of the renal pelvis, has become the most commonly used open surgical procedure. It has a high success rate with few complications in most cases.
One of the biggest advantages of dismembered pyeloplasty is complete excision of a stenotic segment of the UPJ. In fact, nondismembered pyeloplasty is technically easier, in that the ureter is not completely transected from the renal pelvis and tension-free suturing can be easily performed.
Minimally invasive techniques
Endourologic methods applied to UPJ obstruction include the following:
Percutaneous antegrade endopyelotomy
Retrograde ureteroscopic endopyelotomy
In 1983, Wickham and Kellet established access to a hydronephrotic kidney and performed the first percutaneous pyelolysis. The concept was attractive and the technology was available. Soon, a large series of endopyelotomies in adults was reported, with fairly good short- and long-term success rates (70-85%). If an initial attempt of endopyelotomy fails, subsequent open pyeloplasty is still a viable option with a high success rate.
Laceration of the lower pole vessel, which is in anatomic relation with the ureter in 40% of cases, must be avoided. Angiography, endoluminal ultrasonography, spiral (helical) computed tomography (CT), and Doppler ultrasonography have been used to identify the lower-pole vessels. The best recommendation is to make sure that all incisions in the ureteral narrowing are directed laterally so as to minimize the chances of damage to a lower-pole vessel.
Retrograde treatment of UPJ obstruction has been applied to children because of the technical advancements. This technique carries a risk of significant stricture of the lower ureter. Balloon dilatations are most appropriate in pediatric populations because they are the least invasive approach and are associated with the lowest risk of hemorrhage. However, the results generally do not match those of open pyeloplasty, and most pediatric urologists continue to recommend open repair of primary UPJ obstruction.
This technique may be more useful in children older than 4 years with a failed pyeloplasty, in whom only a small dilation of the anastomosis may be required to produce good renal decompression. The technique involves a UPJ bridge with an endopyelotomy stent to drain the kidney and prevent the excessive scar formation that can occur with extensive urinary extravasation. The stent is removed after 6 weeks. Favorable factors include older age, secondary UPJ obstruction, low-grade hydronephrosis, and good renal function.
Laparoscopic pyeloplasty, first introduced in adults in 1993 by Schuessler, yields results that are comparable with those of open pyeloplasty, with success rates reported to be as high as 96-98%, while still maintaining the benefits of endoscopic approaches, including less postoperative pain, short hospitalization, and reduced postoperative recovery time.
The procedure was first described using a transperitoneal approach in children, but soon after, there followed reports of retroperitoneal series, which seemed to require longer operating times, owing to the limits of working space and the more difficult suturing. Robotic assistance (see below) has made the technical demands less significant as a consequence of the enhanced range of motion of the laparoscopic instruments.
The procedure usually requires one camera port and two working ports. However, with the availability of small (3 mm) laparoscopic instrumentation, it is also possible to forgo the working ports and simply place the instruments through small stab incisions in the abdomen. Single-site laparoscopic surgical approaches have also been described.
The choice between a transperitoneal and a retroperitoneal approach, as well as the choice between a dismembered and a nondismembered pyeloplasty, depends on the surgeon’s experience. Numerous reports comparing laparoscopic and open pyeloplasties concluded that postoperative outcomes in the two groups are equivalent in terms of complications, hospital stay, and functional results. Operating time depends on the technical skills required for intracorporeal suturing and proficiency with instrumentation, which can be taught by using surgical simulation with a laparoscopic trainer.
Robotic-assisted pyeloplasty is now a well-established method of correcting UPJ obstruction. It has the advantage of being able to help overcome the difficulties encountered with laparoscopic suturing. The basic principle is similar to that of laparoscopic pyeloplasty, but the suturing in the pelviureteric anastomosis is much easier with the help of an articulated instrument. Its shortcomings are the cost, the instrumentation size, and the difficulty of creating an adequate intra-abdominal working space in small children.
Although the robotic approach has been described, open pyeloplasty remains favored in infants younger than 6 months. Robotic single-site pyeloplasty has been described in adults but has yet to be adapted for use in a pediatric population.
No specific guidelines exist for the deployment of stents or nephrostomy tubes and the duration of their use in the postoperative period. Early work by Davis led to the traditional recommendation of 6 weeks of stent drainage to allow full healing of the ureter. Subsequent investigation, however, showed that a shorter duration (2 weeks) is sufficient.
A double-J ureteral stent can be used, but in children, this requires a second anesthetic for removal of the stent. Ureteropyelostomy stents such as the kidney internal splint stent (KISS), Salle stents, and feeding tubes can be utilized and have the advantage of being removable at the bedside without the need for an anesthetic. This approach is traditionally used for open pyeloplasty but is also described in the laparoscopic setting.
Many series report excellent results with no catheter or stents at all. Factors such as solitary kidney, lower ureteral status, and whether it is a repeat procedure must be taken into consideration upon deciding stent or catheter placement.
Early complications of open pyeloplasty are uncommon and usually involve prolonged urinary extravasation and delayed opening of the anastomosis. Excessive urine leakage via a Penrose drain rarely necessitates stenting. However, if leakage persists for more than 2 weeks, a retrograde indwelling stent can be considered. Delay in opening of the anastomosis is observed most often with the use of a nephrostomy tube without a stent across the anastomosis. Within 3 months of surgery, 80% of obstructed anastomoses eventually open. Bleeding and infection are uncommon.
Intraoperative complications of laparoscopic or robotic pyeloplasty include the following:
Bleeding necessitating transfusion
Trocar damage to viscera or vessels
Thermal damage to tissue or organs
Inspection of the viscera with each step of the operative procedure may help avoid or identify an injury.
Varying degrees of postoperative ileus and abdominal distention can be observed, regardless of the mode of surgery, and can be managed conservatively. Postoperative obstruction is a difficult problem, and it usually occurs at the site of operation. Distal ureteral problems, mostly at the site of the ureterovesical junction, are more common in endoscopic procedures involving multiple instrumentation.
Foley FB. A new plastic operation for stricture at the ureteropelvic junction. J Urol. 1936. 38:643.
Anderson JC, Hynes W. Retrocaval ureter; a case diagnosed pre-operatively and treated successfully by a plastic operation. Br J Urol. 1949 Sep. 21(3):209-14. [Medline].
Ostling J. The genesis of hydronephrosis: Particularly with regard to the changes at the ureteropelvic junction. Acta Chir Scand. 1942. 8:72.
Koff SA, Hayden LJ, Cirulli C, Shore R. Pathophysiology of ureteropelvic junction obstruction: experimental and clinical observations. J Urol. 1986 Jul. 136(1 Pt 2):336-8. [Medline].
Josephson S, Ericson AC, Sjoquist M. Experimental obstructive hydronephrosis in newborn rats. VI. Long-term effects on glomerular filtration and distribution. J Urol. 1985 Aug. 134(2):391-5. [Medline].
Steinhardt GF, Ramon G, Salinas-Madrigal L. Glomerulosclerosis in obstructive uropathy. J Urol. 1988 Nov. 140(5 Pt 2):1316-8. [Medline].
Morrison AR, Nishikawa K, Needleman P. Thromboxane A2 biosynthesis in the ureter obstructed isolated perfused kidney of the rabbit. J Pharmacol Exp Ther. 1978 Apr. 205(1):1-8. [Medline].
Morrison AR, Nishikawa K, Needleman P. Unmasking of thromboxane A2 synthesis by ureteral obstruction in the rabbit kidney. Nature. 1977 May 19. 267(5608):259-60. [Medline].
Yarger WE, Schocken DD, Harris RH. Obstructive nephropathy in the rat: possible roles for the renin- angiotensin system, prostaglandins, and thromboxanes in postobstructive renal function. J Clin Invest. 1980 Feb. 65(2):400-12. [Medline]. [Full Text].
Ishidoya S, Morrissey J, McCracken R, Klahr S. Delayed treatment with enalapril halts tubulointerstitial fibrosis in rats with obstructive nephropathy. Kidney Int. 1996 Apr. 49(4):1110-9. [Medline].
Pimentel JL Jr, Sundell CL, Wang S, Kopp JB, Montero A, Martínez-Maldonado M. Role of angiotensin II in the expression and regulation of transforming growth factor-beta in obstructive nephropathy. Kidney Int. 1995 Oct. 48(4):1233-46. [Medline].
Furness PD 3rd, Maizels M, Han SW, et al. Elevated bladder urine concentration of transforming growth factor- beta1 correlates with upper urinary tract obstruction in children. J Urol. 1999 Sep. 162(3 Pt 2):1033-6. [Medline].
Dressler GR, Wilkinson JE, Rothenpieler UW, et al. Deregulation of Pax-2 expression in transgenic mice generates severe kidney abnormalities. Nature. 1993 Mar 4. 362(6415):65-7. [Medline].
Kim DS, Noh JY, Jeong HJ, et al. Elastin content of the renal pelvis and ureter determines post-pyeloplasty recovery. J Urol. 2005 Mar. 173(3):962-6. [Medline].
Zanardo V, Da Riol R, Faggian D, et al. Urinary beta-2-microglobulin excretion in prematures with respiratory distress syndrome. Child Nephrol Urol. 1990. 10(3):135-8. [Medline].
Huland H, Gonnermann D, Werner B, Possin U. A new test to predict reversibility of hydronephrotic atrophy after stable partial unilateral ureteral obstruction. J Urol. 1988 Dec. 140(6):1591-4. [Medline].
Chiou YY, Shieh CC, Cheng HL, Tang MJ. Intrinsic expression of Th2 cytokines in urothelium of congenital ureteropelvic junction obstruction. Kidney Int. 2005 Feb. 67(2):638-46. [Medline].
Capello SA, Kogan BA, Giorgi LJ, Kaufman RP Jr. Prenatal ultrasound has led to earlier detection and repair of ureteropelvic junction obstruction. J Urol. 2005 Oct. 174(4 Pt 1):1425-8. [Medline].
Kim HJ, Jung HJ, Lee HY, et al. Diagnostic value of anteroposterior diameter of fetal renal pelvis during second and third trimesters in predicting postnatal surgery among Korean population: useful information for antenatal counseling. Urology. 2012 May. 79(5):1132-7. [Medline].
Fernbach SK, Maizels M, Conway JJ. Ultrasound grading of hydronephrosis: introduction to the system used by the Society for Fetal Urology. Pediatr Radiol. 1993. 23(6):478-80. [Medline].
Nguyen HT, Benson CB, Bromley B, Campbell JB, Chow J, Coleman B, et al. Multidisciplinary consensus on the classification of prenatal and postnatal urinary tract dilation (UTD classification system). J Pediatr Urol. 2014 Dec. 10 (6):982-98. [Medline].
Roarke MC, Sandler CM. Provocative imaging. Diuretic renography. Urol Clin North Am. 1998 May. 25(2):227-49. [Medline].
Heyman S, Duckett JW. The extraction factor: an estimate of single kidney function in children during routine radionuclide renography with 99mtechnetium diethylenetriaminepentaacetic acid. J Urol. 1988 Oct. 140(4):780-3. [Medline].
Ham WS, Jeong HJ, Han SW, et al. Increased nephron volume is not a cause of supranormal renographic differential renal function in patients with ureteropelvic junction obstruction. J Urol. 2004 Sep. 172(3):1108-10. [Medline].
Kincaid W, Hollman AS, Azmy AF. Doppler ultrasound in pelviureteric junction obstruction in infants and children. J Pediatr Surg. 1994 Jun. 29(6):765-8. [Medline].
Mearini L, Rosi P, Zucchi A, et al. Color Doppler ultrasonography in the diagnosis of vascular abnormalities associated with ureteropelvic junction obstruction. J Endourol. 2003 Nov. 17(9):745-50. [Medline].
Katayama H, Yamaguchi K, Kozuka T, et al. Adverse reactions to ionic and nonionic contrast media. A report from the Japanese Committee on the Safety of Contrast Media. Radiology. 1990 Jun. 175(3):621-8. [Medline].
Ritter L, Götz G, Sorge I, Lehnert T, Hirsch FW, Bühligen U, et al. Significance of MR Angiography in the Diagnosis of Aberrant Renal Arteries as the Cause of Ureteropelvic Junction Obstruction in Children. Rofo. 2014 Sep 16. [Medline].
Parikh KR, Hammer MR, Kraft KH, Ivančić V, Smith EA, Dillman JR. Pediatric ureteropelvic junction obstruction: can magnetic resonance urography identify crossing vessels?. Pediatr Radiol. 2015 Nov. 45 (12):1788-95. [Medline].
Whitaker RH. Methods of assessing obstruction in dilated ureters. Br J Urol. 1973 Feb. 45(1):15-22. [Medline].
Whitaker RH. The Whitaker test. Urol Clin North Am. 1979 Oct. 6(3):529-39. [Medline].
Koff SA, Binkovitz L, Coley B, Jayanthi VR. Renal pelvis volume during diuresis in children with hydronephrosis: implications for diagnosing obstruction with diuretic renography. J Urol. 2005 Jul. 174(1):303-7. [Medline].
Solari V, Piotrowska AP, Puri P. Altered expression of interstitial cells of Cajal in congenital ureteropelvic junction obstruction. J Urol. 2003 Dec. 170(6 Pt 1):2420-2. [Medline].
Koff SA, Campbell KD. The nonoperative management of unilateral neonatal hydronephrosis: natural history of poorly functioning kidneys. J Urol. 1994 Aug. 152(2 Pt 2):593-5. [Medline].
Koff SA. The case for nonoperative management of apparent UPJ obstruction. Invest Urol. 1991. 14:5.
Song SH, Lee SB, Park YS, Kim KS. Is antibiotic prophylaxis necessary in infants with obstructive hydronephrosis?. J Urol. 2007 Mar. 177(3):1098-101; discussion 1101. [Medline].
Braga LH, Farrokhyar F, D'Cruz J, Pemberton J, Lorenzo AJ. Risk factors for febrile urinary tract infection in children with prenatal hydronephrosis: a prospective study. J Urol. 2015 May. 193 (5 Suppl):1766-71. [Medline].
Pettersson BA, Aperia A, Elinder G. Pathophysiological changes in rat kidneys with partial ureteral obstruction since infancy. Kidney Int. 1984 Aug. 26(2):122-7. [Medline].
Koff SA, Campbell K. Nonoperative management of unilateral neonatal hydronephrosis. J Urol. 1992 Aug. 148(2 Pt 2):525-31. [Medline].
Ransley PG, Dhillon HK, Gordon I, et al. The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J Urol. 1990 Aug. 144(2 Pt 2):584-7; discussion 593-4. [Medline].
Cartwright PC, Duckett JW, Keating MA, et al. Managing apparent ureteropelvic junction obstruction in the newborn. J Urol. 1992 Oct. 148(4):1224-8. [Medline].
Sampaio FJ, Favorito LA. Ureteropelvic junction stenosis: vascular anatomical background for endopyelotomy. J Urol. 1993 Dec. 150(6):1787-91. [Medline].
Tasian GE, Casale P. The Robotic-Assisted Laparoscopic Pyeloplasty: Gateway to Advanced Reconstruction. Urol Clin North Am. 2015 Feb. 42(1):89-97. [Medline].
Hanson GR, Castle EP, Ostlie DJ, Holcomb GW, Murphy JP, Gatti JM. The use of stab incisions for instrument access in laparoscopic urological procedures. J Urol. 2004 Nov. 172 (5 Pt 1):1967-9. [Medline].
Khambati A, Wehbi E, Farhat WA. Laparo-endoscopic single site surgery in pediatrics: Feasibility and surgical outcomes from a preliminary prospective Canadian experience. Can Urol Assoc J. 2015 Jan-Feb. 9 (1-2):48-52. [Medline].
Avery DI, Herbst KW, Lendvay TS, Noh PH, Dangle P, Gundeti MS, et al. Robot-assisted laparoscopic pyeloplasty: Multi-institutional experience in infants. J Pediatr Urol. 2015 Jun. 11 (3):139.e1-5. [Medline].
Buffi NM, Lughezzani G, Fossati N, Lazzeri M, Guazzoni G, Lista G, et al. Robot-assisted, single-site, dismembered pyeloplasty for ureteropelvic junction obstruction with the new da Vinci platform: a stage 2a study. Eur Urol. 2015 Jan. 67 (1):151-6. [Medline].
Mandhani A, Kapoor R, Zaman W, Kumar A, Bhandari M, Gambhir S. Is a 2-week duration sufficient for stenting in endopyelotomy?. J Urol. 2003 Mar. 169 (3):886-9. [Medline].
Taveres A, Manaboriboon N, Lorenzo AJ, Farhat WA. Insertion of an internal-external nephroureteral stent during pediatric laparoscopic pyeloplasty: description of the technique. Urology. 2008 Jun. 71 (6):1199-202. [Medline].