UPJ Obstruction in the Adult Population: Are Crossing Vessels Significant?

Techniques & Technology

TECHNIQUES & TECHNOLOGY UPJ Obstruction in the Adult Population: Are Crossing Vessels Significant? Michael Grasso III, MD, Robert P. Caruso, MD, Courtney K. Phillips, MD New York University School of Medicine, New York Ureteropelvic junction (UPJ) obstruction describes various causes of impaired drainage at the UPJ. Regardless of the cause, the end result is the same: impedance in the normal flow of urine from the renal pelvis into the proximal ureter, resulting in caliectasis and hydronephrosis. This may lead to progressive deterioration of renal function and, thus, often requires intervention to relieve the obstruction and restore the normal flow of urine. Defining the pertinent anatomy, the degree of obstruction, and differential renal function is key to determining whether and when intervention is necessary. [Rev Urol. 2001;3(1):42-50, 61] Key words: Angiography • Hydronephrosis • Laparoscopy • Pyeloplasty • Ultrasonography • Ureteropelvic junction C ontemporary management of the obstructed ureteropelvic junction (UPJ) in the adult has evolved. While open surgical intervention was once considered the standard of care, today there are a myriad of minimally invasive treatments to alleviate obstruction of a hydronephrotic, poorly draining kidney. Urologists now have to choose which treatment is best, weighing efficacy with length of hospital stay, intraoperative and perioperative risks, and patient satisfaction. The association of polar renal vessels with UPJ obstruction is of particular concern with minimally invasive techniques, because inadvertent transection of these vessels may lead to intraoperative hemorrhage and may also be associated with higher failure rates. We will explore the current minimally invasive treatments for patients with UPJ obstruction and, specifically, the impact that crossing vessels have on the morbidity of these procedures. In addition, we will review the various ways of identifying and localizing associated vessels. Epidemiology The incidence of UPJ obstruction is less well defined in adults than in children. In the pediatric age group, it is the most common cause of upper urinary tract dilation, accounting for 80% of all dilated collecting systems identified antenatally by fetal ultrasonography.1 A significant number of these dilated systems will require intervention eventually; some patients may not present with functional obstruction until adulthood. The male-to-female predominance is greater than 2:1, and the left kidney is affected about twice as often as the right.1 Though UPJ obstruction occurs in adults less frequently than in neonates, it is not a rarity. 42 REVIEWS IN UROLOGY WINTER 2001 UPJ Obstruction Etiologies of UPJ Obstruction UPJ obstruction from congenital causes may result from either an anatomic or a physiologic defect in the upper ureter. Primary luminal narrowing may be caused by an incomplete recanalization process in utero at the cephalad end of the developing ureter.1,2 Partial obstruction can result from an anomalous number or arrangement of smooth muscle cells within the upper ureteral wall causing peristaltic dysfunction. In the involved segment, the smooth muscle layer may be hypertrophied or virtually absent.1,2 Rarely, ureteral pleats or folds that contain all layers of the ureter can act as valves and cause obstruction (Figure 1).1,2 Acquired stenosis of the UPJ can result from upper tract infections, stones, trauma (eg, instrumentation), or ischemia, which can all cause reactive fibrosis and an annular stricture (Figure 2). Fibrosis may worsen or become a secondary process in the face of a preexisting partial obstruction. Extrinsic compression secondary to retroperitoneal fibrosis, for example, may also tent or twist the ureter, adding to the overall obstruction. Retroperitoneal processes may also result in functional obstruction. The kidneys float in the retroperitoneum, with their main anchor being the renal A Main Points • Crossing vessels compressing or distorting the ureteropelvic junction (UPJ) may be the sole cause of ureteral outflow obstruction or may coexist with other causes of UPJ obstruction. • In patients with a possible UPJ obstruction, retrograde ureteropyelography can be useful in defining the subtype of anatomic defect and in ensuring the normalcy of the rest of the ureter. • Endoluminal ultrasonography has the potential to become the diagnostic tool of choice for localizing crossing vessels. • The current recommendation is to image before endoscopic incision (preoperatively or intraoperatively) to detect crossing vessels associated with an obstructed UPJ. • The standard of treatment for patients with UPJ obstruction is still open pyeloplasty. • Laparoscopic pyeloplasty has success rates similar to the open technique but is technically challenging. hilum. If the kidney is more mobile than the ureter secondary to ureteral or retroperitoneal fibrosis, obstruction can occur with each respiration or in certain positions; for example, there may be obstruction when the patient is erect but not supine.2 Abnormal insertion of the ureter results in high-insertion UPJ obstruction. The ureter inserts into the renal pelvis in a high and often oblique manner, which can cause functional obstruction (Figure 3). Normally, the ureter inserts in the most dependent portion of the renal pelvis. It is unclear whether this is a primary developmental anomaly or a secondary effect of a diseased ureter, with development of a specific B Figure 1. Ureteral folds noted below a hydronephrotic kidney. (A) Proximal ureteral folds are seen obstructing the ureteropelvic junction on the retrograde ureteropyelogram. (B) Corresponding intraluminal sonographic image defines a plexus of veins arising from the gonadal vein, creating this ureteral pattern of valvular-like folds. (Used with permission from Gitlin J, Grasso M.39) type of renal pelvic dilation below the area of insertion. The greater the hydronephrosis, the worse the obstruction in these cases (the ureteral insertion resides higher on the renal pelvis, creating acute angulation).2 High-insertion UPJ obstructions are particularly amenable to minimally invasive management. By incising the common wall composed of the most proximal ureter and renal pelvis, the UPJ is brought to a dependent position with a funneling effect that will improve drainage. Crossing vessels compressing or distorting the UPJ may be the sole cause of ureteral outflow obstruction. More commonly, however, they coexist with other causes of UPJ obstruction. Aberrant vasculature, arising from the renal vessels, aorta, vena cava, or iliac vessels that supply the lower pole of the kidney are frequently associated with the collecting system (Figure 4). From 25% to 50% of UPJ obstructions are found to have this relationship, whether causative or coincidental.2,3 It is paramount to note that these vessels pose a threat of hemorrhage during minimally invasive therapies designed to create renal pelvic funneling and relieve the obstruction at the UPJ. In addition, crossing vessels have also been shown to be a significant negative prognosticator. Van Cangh and colleagues3,4 demonstrated that the presence of crossing vessels decreased WINTER 2001 REVIEWS IN UROLOGY 43 UPJ Obstruction continued the success rate of antegrade endopyelotomy from 86% to 42%. With long-term follow-up (mean, 6.5 years), the success rate declined to 33% of those patients who presented initially with associated UPJ vessels and underwent this form of minimally invasive therapy.5 Diagnosis Adults with a UPJ obstruction can present with acute renal colic or chronic back pain. Other nonspecific signs include hematuria, urinary tract infections, and/or pyelonephritis.1,2 The pain may be correlated with periods of increased fluid intake or ingestion of a food with diuretic properties, prompting the Dietl crisis. Rarely, hypertension secondary to hyperreninemia can be one of the presenting symptoms.1 The evaluation of a hydronephrotic kidney in an adult commonly begins with either renal sonography, CT scan of the abdomen/pelvis, and/or an intravenous pyelogram. It is important to not immediately equate dilation of the intrarenal collecting system with obstruction or increased renal pelvic pressures. A nuclear medicine renal A B E D 44 scan with an added diuretic phase (eg, MAG-3, diethylenetriamine pentaacetic acid) is often employed to determine the significance of renal pelvic dilation in terms of functional compromise. To best quantify the degree of obstruction with this study, the patient should be properly hydrated, the bladder should be completely drained (with a catheter, if necessary, if there is significant bladder outlet obstruction), and the administration of a diuretic should occur when the emission is maximized in the renal pelvis. Anatomic obstruction is defined as clearance of half of the radioisotope from the renal pelvis (ie, t¹⁄₂) in longer than 20 minutes. When the renal pelvis is particularly dilated, or if the results from the nuclear medicine renal scan are equivocal, a Whitaker antegrade pressureflow study may be employed to help clarify the presence or extent of a UPJ obstruction. This is performed with a small-diameter percutaneous nephrostomy, instilling dilute contrast under real-time fluoroscopy and measuring the intrarenal collecting system pressure with an in-line manometer. In large dilated systems, the renal pelvis must completely fill before assessing REVIEWS IN UROLOGY WINTER 2001 pressure. Renal drainage down the ureter with intrarenal pressures up to 15 cm H20 are considered normal, while those higher than 20 cm H20 represent obstruction.6 If a UPJ obstruction is defined or suspected with 1 of the previous imaging modalities, retrograde ureteropyelography is often useful to define the subtype of anatomic defect that is present and to ensure the normalcy of the rest of the ureter. Is this a high-insertion or annular-stricture subtype, for example? Retrograde ureteropyelography may also give insight into associated lesions or anatomy. A proximal right ureter that turns abruptly toward the midline and back may reflect a retrocaval anomaly or a primary retroperitoneal process, for instance. Treatment Options Surgical intervention is warranted when deterioration of renal function is evident and/or when the associated symptoms are progressive or severe. The goal of treatment is to improve renal drainage, maintain or improve renal function, and aid in the resolution of symptoms. The standard of treatment is still C Figure 2. Annular stricture causing a ureteropelvic junction (UPJ) obstruction in a 40-year-old man with new symptoms of renal colic. (A) The short, annular nature of the obstructing segment (with a guide wire passing through it) is observed on a retrograde ureteropyelogram. (B) An annular-like ureteral stricture, very similar to the more common urethral stricture, is seen on endoscopy. (C) Endoscopic view defines a safety guide wire through the strictured segment that is no more than 2 mm in diameter. (D, E) Seen on endoscopy, a posterolateral incision opens the strictured UPJ. More than 3 years following surgery, this patient has normal renal function and drainage, confirmed on serial nuclear medicine renal scans. UPJ Obstruction Figure 3. Three-dimensional reconstruction of a high-insertion ureteropelvic junction (UPJ) obstruction. The center of the image corresponds to the intraluminal sonographic probe, which is cylindric. From left to right, large anterior medial crossing vessels are noted. In addition, a common wall, composed of the renal pelvis and proximal ureter, is acting as a flap valve. This patient had undergone a previous endopyelotomy, using the Acucise device, in which a lateral incision unsuccessfully opened the UPJ. In light of renal rotation, this high insertion was incised in a purely posterior direction, which facilitated funneling at the UPJ, relieving the obstruction. (Used with permission from Giddens JL, Grasso M. J Urol. 2000.17) open pyeloplasty, with success rates approaching 95%. This was first described by Trendelenburg in 1886.7 Several variations have since evolved, and today the Anderson-Hynes dismembered pyeloplasty is the most commonly employed open surgical approach. It can be used for both high or dependent ureteral insertions and for lengthy, tortuous proximal ureteral segments.1,6 The Foley Y-V plasty is a flap technique best suited for high ureteral insertions. It does not significantly reduce renal pelvic size and, as with other flap techniques, it cannot be combined with transposition of a lower-pole vessel. Spiral and vertical flaps, such as the Culp or Scardino, are useful when long, strictured segments of proximal ureter are present. Using these techniques, the proximal ureter is reconstructed with tubularized redundant portions of the renal pelvis. Ureterocalicostomy, anastomosis of the ureter to the lower-pole calyx with modest partial lower-pole nephrectomy, is most often reserved for failed open pyeloplasty when there is an intrarenal pelvis and/or significant hilar scarring.4 Adults with primary (congenital) or secondary UPJ obstruction are most commonly treated with endoscopic incision, which offers excellent success rates with minimal invasion and morbidity as well as prompt return to normal activity. Minimally invasive treatments for UPJ obstruction began with the work of David M. Davis and colleagues8,9 in 1943. He described the intubated ureterotomy, a procedure in which a segment of ureter was incised and then allowed to heal over a scaffolding, very similar to the current internal double pigtail stent method. Davis’ work was focused on ureteral stricture disease, but the principles of splinting the ureter after incision and of meticulous drainage directing urine away from this area underscore the fact that the ureter has a great propensity to heal with recanalization. The first endopyelotomy was described by Wickham and Kellet10 in the early 1980s and was further refined and popularized by Smith and Badlani.11 Specifically, this endopyelotomy was performed percutaneously with a rigid nephroscope and cold knife, which was used to incise the obstructed UPJ and bring it to a more dependent position. Smith’s initial application of a nephroureteral stent to splint the incised UPJ involved placing a 14F segment through the incision site. This evolved to separate nephrostomy and 14/7F internal stent; the nephrostomy tube was removed in the immediate postoperative period. The large-diameter “endopyelotomy” stent is thought to develop a larger diameter UPJ after endoscopic incision. Other refinements have included a smaller percutaneous access sheath combined with endoscope miniaturization to decrease the morbidity of the procedure in general. Figure 4. Intraluminal sonographic image of the ureteropelvic junction (UPJ) defining an associated large posterior crossing vessel. The patient’s contralateral kidney had been removed for poor function secondary to a UPJ obstruction. This patient underwent an antegrade endopyelotomy in which a lateral incision was performed, avoiding this vessel. She subsequently re-presented with obstruction 1 year postoperatively. At open pyeloplasty, the large posterior vein was confirmed. Success with antegrade endopyelotomy was reported by Motola and colleagues,12 who treated 200 patients over an 8-year period, obtaining an overall success rate of 86%. In this series, there was no difference between final success rates for primary and secondary UPJ obstruction managed in this fashion. Retrograde management of UPJ obstruction was reported by Bagley and associates13 in 1985 and by Inglis and Tolley14 in 1986. The retrograde endopyelotomy has evolved from rigid to flexible ureteroscopes employed to manage the obstructing segment of ureter. Different methods of incising the UPJ have likewise developed. Endoscopic cold knife, balloon dilator, endopyelotome, pencil-tipped Bugbee electrode, and holmium laser energy have all been employed in a retrograde fashion to dilate or incise the UPJ, with success rates similar to those of percutaneous antegrade approaches.15-17 A common technique is based on contrast imaging (ie, retrograde ureteropyelography) followed by direct endoscopic inspection of the UPJ. In female patients, this is frequently performed with a semi-rigid ureteroscope, while in males, the actively deflectable, WINTER 2001 REVIEWS IN UROLOGY 45 UPJ Obstruction continued flexible endoscope is often required, particularly if the ureter has not been prestented. In some centers, intraluminal sonography is used intraoperatively, to avoid associated vasculature during the incision and to ensure that the direction of the incision will optimize the result (Figure 5).17-19 The incision is made full thickness through the ureteral wall, and an internal stent is placed for up to 8 weeks to facilitate drainage and healing. The 14F segment of an endopyelotomy stent (commonly used in an antegrade fashion) cannot be passed easily through the distal ureter and, thus, is infrequently used for retrograde endopyelotomy. Most often, smaller-diameter (6F to 10F) doublepigtail stents are placed in this setting. Clayman and coworkers20 published an extensive study of retrograde endopyelotomies managed with a relatively large, rigid ureteroscope and an angled electrocautery probe. They found that the majority of patients had improved drainage but that the rate of distal ureteral stricture, as a complication of the overall procedure, was significant. The investigators subsequently developed a combined balloon dilation and cutting device (Acucise).21 This device is employed, not under di- rect vision but, rather, fluoroscopically and is analogous to a papillotome used by gastroenterologists to incise the ampulla of Vater. This technique is based on a pure lateral incision, with results comparable to other techniques. The potential downsides of this technique include the inability to adjust the incision based on direct endoscopic assessment (ie, from lateral to posterior, for example, to compensate for renal rotation) and the reported risk of intraoperative hemorrhage even with a pure lateral incision.22,23 Retrograde endopyelotomy, performed either under direct vision or with fluoroscopic guidance with the Acucise device, is based on principles similar to those associated with the initial antegrade technique, in that an incision is made through the obstructing segment and the area is stented to help facilitate healing. In general, the aforementioned procedures are designed to bring the UPJ to a more dependent position away from the diseased segment and to facilitate funneling, all in an attempt to improve drainage. Laparoscopic pyeloplasty is being performed at centers and appears to closely approach the success rates for open pyeloplasty while offering the ad- A B C D 46 REVIEWS IN UROLOGY WINTER 2001 vantages of minimal invasiveness and quick recovery. It can be done on patients with UPJ obstruction for whom surgery with retrograde or percutaneous antegrade incisions has failed or on those who have an extremely dilated renal pelvis and otherwise may not be candidates for endoscopic incisional techniques. Crossing vessels may also be easily avoided under magnified endoscopic imaging. A small intrarenal pelvis is a relative contraindication. Chen and colleagues24 reported their results from 57 patients, 50 with primary and 7 with secondary repairs after failing other minimally invasive forms of therapy. Mean operative time was 4.3 hours, and mean hospital stay was 3.3 days. The investigators reported that 30 (53%) of 57 patients had crossing vessels that were avoided. All 7 of the secondary repairs were successful, with follow-up of more than 1 year. There was 1 clinical and 1 radiologic failure in the primary repair group. Another report by Bauer and associates25 compared laparoscopic (n = 42) with open pyeloplasty (n = 35) and defined similar success (98% vs 94%) and complication rates (12% vs 11%) for the respective procedures. Because laparoscopic pyeloplasty is technically Figure 5. A 32-year-old woman presented with moderate azotemia and bilateral hydronephrosis. Right retrograde ureteropyelography demonstrated a redundant proximal ureter and ureteropelvic junction (UPJ) obstruction. (A) Intraluminal sonography defined a common wall posteriorly and medially between the proximal ureter and renal pelvis. An incision was made in the posterior medial segment. (B) An intravenous pyelogram (6 months after treatment for the right side) showed the right kidney draining promptly with funneling at the UPJ. The left kidney continued to drain poorly and, at this time, the patient experienced episodic colic. (C) A retrograde ureteropyelogram on the left side defined a similar anatomic variant; at this time, a posterior medial incision was made to divide a common wall. (D) Intravenous pyelography, performed 6 months thereafter, defines prompt symmetric renal function and immediate drainage bilaterally. UPJ Obstruction challenging and time-consuming, it may not be practical for most local centers to use as a primary repair technique. It will likely increase in popularity at select centers where patients are referred after failed endoscopic treatment, for those with crossing vessels that are difficult to avoid endoscopically, and for those with a particularly dilated collecting system requiring a reduction pyeloplasty. Imaging of Crossing Vessels During the past decade, the urologist’s ability to visualize vessels crossing the UPJ has improved. Earlier attempts to image these vessels relied on intravenous urography to detect abnormalities in the silhouette of the UPJ, thought to be indicative of crossing vessels. One of the signs used most often was the “short segment sign,” seen as an area of contrast collection between the UPJ obstruction and the crossing vessels. Though a study by Hoffer and Lebowitz26 showed a 60% sensitivity rate for this sign, attempts to use this as a means of diagnosis by Cassis and coworkers27 yielded a 20% specificity rate. A minimally invasive technique used to visualize crossing vessels is helical CT angiography (HCTA). In a series of 24 consecutive patients with symptomatic UPJ obstruction, 11 of 24 patients were found to have crossing vessels with HCTA visualization.28 Of those patients, 5 were treated with either laparoscopic or open pyeloplasty, which revealed 100% concordance with the HCTA findings. Farres and colleagues29 reported similar findings. In this series, 20 patients were examined with HCTA augmented by 3-dimensional reconstruction, and these results were compared with findings noted during open pyeloplasty. Thirteen of the 20 patients were found to have crossing vessels on HCTA, and these findings were confirmed at surgery. In a study that directly compared digital subtraction angiography (DSA) and HCTA, Rouviere and coworkers30 found that if DSA is used as the stan- dard, then HCTA is highly sensitive and specific in defining crossing arteries. Despite these results, the major downfall of DSA’s diagnostic capabilities is its failure to detect veins as they cross the UPJ. Though all associated arteries were detected by DSA in this study, associated veins, which occurred in 10 of the 12 patients, were only visualized with HCTA. MRI angiography has also been used in this setting to localize associated UPJ arteries, but it may have some of the same limitations as DSA in defining associated veins.31 Endoluminal ultrasonography is a technique in which small diameter (6F) sonographic probes are placed in the ureter, usually at the same time as endopyelotomy, to evaluate the nature of the UPJ obstruction and to localize any adjacent vasculature before endoscopic incision.32 The area examined is 2 cm surrounding the 12.5 MHz probe, for example. It is a particularly useful modality, in that real-time imaging is obtained intraoperatively, so adjustments in the location and extent of the endoscopic incision can be made accordingly.33,34 Intraluminal sonography has been useful in avoiding associated vasculature and in ensuring complete incision through a particularly long segment of ureter associated with a highinsertion variant.33,34 It can also direct incisions in directions that were not obvious with other modalities. In a recent series of retrograde endopyelotomies performed under intraluminal sonographic guidance, Giddens and Grasso17 directed endoscopic incisions posteromedially in 3 patients in whom renal rotation was defined with this imaging modality; all had improved drainage postoperatively. When compared with HCTA, Siegel and associates35 found that endoluminal ultrasonography identified more crossing vessels in the population of patients with UPJ obstruction studied. Of the patients who underwent subsequent laparoscopy, complete agreement was noted between the imaging modalities and surgical findings. Keeley and colleagues36 also studied prospectively these 2 imaging modalities. Intraluminal sonography defined significantly more vessels than HCTA in this study. In addition, sonographic imaging was particularly useful intraoperatively by changing the direction of the endoscopic incision in 4 patients and by ensuring a complete incision through high-insertion variants. Endoluminal ultrasonography thus has the potential to become the diagnostic tool of choice for localizing crossing vessels. Its ability to identify both arteries and veins makes it superior to DSA. It can approximate vessel size and determine the dynamic location of vessels with respirations. Furthermore, it may be employed immediately before endopyelotomy to delineate the dynamic location of vessels that can change with respirations, thus facilitating the proper placement, depth, and length of the endopyelotomy incision. Another minimally invasive method currently being studied as a means to diagnose crossing vessels associated with a UPJ obstruction is color Doppler sonographic imaging (CDI). Frauscher and coworkers37 compared CDI with and without enhancing intravenous sonographic contrast. Fifteen of 29 patients were found to have crossing vessels confirmed with nonenhanced CDI, while 22 of 29 patients were found to have crossing vessels when contrast was administered. Six of the 7 vessels missed without contrast were veins. This study demonstrates that CDI without contrast is not effective in visualizing veins and small arteries and that neither enhanced nor nonenhanced CDI can approximate vessel size, because of color blooming. For these reasons and because there is a relatively long learning curve, CDI is not yet popular for this application. Anatomy of Crossing Vessels Though several imaging methods are available to visualize crossing vessels preoperatively, the use of imaging tech- WINTER 2001 REVIEWS IN UROLOGY 49 UPJ Obstruction continued niques before surgery has been controversial. It has been stated that localizing vessels associated with a UPJ obstruction is unnecessary when an endopyelotomy is performed with a traditional posterolateral incision. This technique does, however, carry with it the risk of vessel transection, as demonstrated by Sampaio,38 who performed an extensive study of cadaveric kidneys, employing casts of the vessels and collecting systems. In his study of 546 renal units, Sampaio found that 65.1% of kidneys had crossing vessels on the ventral surface of the UPJ, while 6.2% had crossing vessels posteriorly. In addition, 20.5% of kidneys had posterior crossing vessels within 1.5 cm of the UPJ. This is within the area where an inadvertent transection could occur during a posterolateral endopyelotomy incision. In no kidney in this study were vessels in the lateral portion of the UPJ noted, leading Sampaio to conclude that an incision in this direction may avoid intraoperative hemorrhage. Sampaio’s anatomic study is an elegant one, but its clinical utility in cases of UPJ obstruction is limited because the kidneys studied were neither obstructed at the UPJ nor hydronephrotic. Both of these pathologic findings can alter the anatomic pattern of crossing vessels.33 Bagley’s findings, in fact, demonstrate that kidneys with a UPJ obstruction may have a 3-timesgreater risk of having crossing vessels than kidneys without obstruction and that kidneys affected by secondary UPJ obstruction are altogether unpredictable in their structure, since prior manipulation and scarring can change previously visualized anatomy.33 Though crossing vessels in the lateral segment may be the least common site when associated with a UPJ obstruction, studies have demonstrated that anterior or posterior crossing vessels frequently have a lateral component and that, in some instances, the vessels may be directly lateral to the UPJ.34 Rouviere and associates30 reported that of 12 kidneys with crossing vessels, 10 vessels were anterolateral. Even when a pure lateral incision is performed, which is the preferred direction of the Acucise balloon’s cutting wire, bleeding complications can still occur and have been reported.22,23 Both Streem22 and Stoller,23 at separate institutions, have reported bleeding complications associated with this technique. Given the unpredictability of crossing vessels associated with an obstructed UPJ, the current recommendation from most centers is to image preoperatively or intraoperatively before endoscopic incision. It has been particularly useful in avoiding bleeding complications and in directing surgical technique. At certain centers, for example, the intraoperative (ie, intraluminal) imaging defined the location of a highinsertion septum that was not lateral and, thus, required a different direction of incision.17-19,36 In addition, imaging also defined a subgroup of patients who had either complex associated vasculature or other anatomic variants that were thought to prohibit a successful endoscopic incision and who were directed to either laparoscopic or open surgical therapies.17,33,36 Conclusions Endoscopic management of the obstructed UPJ has, with good reason, become a common treatment modality. Although the presence of crossing vessels does not seem to play a major role in the pathogenesis of UPJ obstruction, it can significantly impact the prognosis and treatment of those patients in whom these vessels occur. When performing an endoscopic incision, the risk of perioperative hemorrhage is reduced but not eliminated when this is performed in the lateral segment. Potential complications from transecting crossing vessels in this area include hemorrhage and significant loss of functioning renal parenchyma. In addition, lateral incisions may not properly divide a high-insertion septum, especially if there is renal rotation, thus producing a suboptimal result. With the high accuracy of minimally invasive diagnostic techniques (eg, HCTA, MRI angiography, and endoluminal ultrasonography), preoperative or intraoperative imaging of the UPJ anatomy can—potentially—further reduce the rate of complications, maximize the surgical outcome and, in select cases, determine when alternative methods of treatment are necessary. ■ References 1. Bauer SB. Anomalies of the kidney and ureteropelvic junction. In: Walsh PW, Retik AB, Vaughan ED Jr, Wein AJ, eds. Campbell’s Urology. 7th ed. Philadelphia: WB Saunders Company; 1998:1739-1749. 2. Park JM, Bloom DA. The pathophysiology of ureteropelvic junction obstruction. Urol Clin North Am. 1998;25:161-169. 3. 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