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Crossing Vessels at the Ureteropelvic Junction: Detection with Contrast-enhanced Color Doppler Imaging

¹ Departments of Radiology II (F.F., G.H., D.z.N.)
² Urology (G.J., H.S., G.B.), University Hospital Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria.

	Abstract

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To investigate the feasibility of imaging crossing vessels at the ureteropelvic junction (UPJ) preoperatively by means of contrast agent–enhanced color Doppler imaging (CDI).

MATERIALS AND METHODS: Twenty-nine patients (13 female patients, 16 male patients; age range, 17–76 years; mean age, 45 years) with symptomatic UPJ obstruction were examined with CDI before and after intravenous infusion of the contrast agent. The type (ie, arterial or venous) and position of the vessel relative to the UPJ (ie, anterior or posterior) were assessed. The CDI findings were correlated with the surgical findings at laparoscopic pyeloplasty.

RESULTS: Among the 29 patients, crossing vessels were detected with nonenhanced CDI in 15 patients, with enhanced CDI in 22 patients, and with laparoscopy in 23 patients. Enhanced CDI depicted crossing vessels in 22 (96%) of the 23 laparoscopically confirmed cases compared with nonenhanced CDI, which depicted 15 (65%) of the 23 cases. The rate of detecting crossing vessels increased significantly with use of the contrast agent (P < .016, McNemar test).

CONCLUSION: Compared with nonenhanced CDI, contrast-enhanced CDI significantly improves the detection of crossing vessels at the UPJ and is useful in the presurgical evaluation of UPJ obstruction.

Index terms: Kidney, stenosis or obstruction, 812.842, 813.842 • Renal arteries, US, 961.12983, 961.12988 • Renal veins, US, 966.12983, 966.12988 • Ultrasound (US), contrast media, 821.12983, 821.12988, 961.12983, 961.12988, 966.12983, 966.12988 • Ultrasound (US), Doppler studies, 821.12983, 821.12988, 961.12983, 961.12988, 966.12983, 966.12988 • Ureter, stenosis or obstruction, 821.842

	Introduction

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
The results of clinical and experimental studies (1) suggest that the underlying cause of ureteropelvic junction (UPJ) obstruction may be a disturbance in pelvic peristalsis due to abnormal orientation of muscle fibers at the UPJ. Consequently, the peristaltic waves from the pelvis cannot propagate across the UPJ, and this results in hydronephrosis. The importance, if any, of vessels crossing the UPJ and thus causing obstruction remains controversial, but the existence of these vessels in the adult population with UPJ obstruction is much greater than that in the general population (2–5). Crossing vessels, when present, usually cross anteriorly to the UPJ; posteriorly crossing vessels are less commonly encountered. According to Van Cangh et al (6), recognition of these vessels is the single most important prognostic factor in the success of treatment with endopyelotomy.

Currently, UPJ repair is performed with minimally invasive endourologic techniques such as endopyelotomy by making a longitudinal incision in the ureter with a cutting device passed either in the retrograde direction through the ureter or in the antegrade direction through a dilated percutaneous nephrostomic track (7,8). An additional method is laparoscopic pyeloplasty, which is preferred over the more invasive open pyelotomy (9,10). Vascular injuries are more likely to occur when the investigator fails to recognize crossing vessels during an endourologic procedure. To avoid vascular injuries, many investigators request preoperative or intraoperative imaging studies such as renal arteriography, spiral computed tomography (CT), or endoluminal ultrasonography (US) in an attempt to demonstrate crossing vessels, but each of these studies involves some degree of invasiveness (11–15). Therefore, a relatively inexpensive and minimally invasive method of vessel detection such as color Doppler imaging (CDI) without the use of an iodinated contrast agent appears to be desirable.

The purpose of this study was to investigate the ability of CDI to depict crossing vessels in 29 symptomatic patients with UPJ obstruction. We also evaluated the feasibility of the use of an intravenously administered US contrast agent, SH U 508A (Levovist; Schering, Berlin, Germany), to improve CDI flow detection within crossing vessels.

	MATERIALS AND METHODS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Study Population
For 16 months, 29 patients (13 female patients and 16 male patients; mean age, 45 years; age range, 17–76 years) with primary (n = 28) and secondary (n = 1) UPJ obstruction were entered into our study. All patients were symptomatic, and UPJ obstruction was confirmed on the basis of urographic study results. The classic findings at urography included dilatation of the renal pelvis and calices and absent or delayed opacification of the ureter, with a bandlike narrowing at the UPJ (11). At CDI examination, five patients had indwelling ureteral stents, whereas two patients had percutaneous nephrostomic catheters. All patients enrolled in our study were candidates for laparoscopic pyeloplasty.

CDI Examinations
All CDI examinations were performed by a single radiologist (F.F.) by using a model 128 XP/10 (Acuson, Mountainview, Calif) or Sonoline Elegra (Siemens) unit equipped with color Doppler software and 3.5- and 5.0-MHz phased-array sector transducers operating at Doppler frequencies of 2.5, 3.5, and 4.0 MHz. Initially, real-time US was performed to identify the UPJ. For assessment of the UPJ, that is, in case of transient dilatation of the collecting system, all patients were well hydrated at the time of the US examination.

Nonenhanced CDI.—Color Doppler imaging was performed to visualize and map the position (ie, anterior or posterior) of the crossing vessel relative to the UPJ. CDI was performed in both the color Doppler frequency mode and the color Doppler amplitude mode. Standardized machine settings (transmit power, < 500 mW/cm²; a low pass wall filter; and medium persistence) were used and remained fixed throughout the study. These settings were chosen to maximize sensitivity to low-velocity and low-volume blood flow. The color Doppler gain was optimized by increasing the gain until noise appeared and then reducing the gain until it was just suppressed (usually about 60%–70% gain). The color Doppler amplitude gain was optimized by increasing the gain until the first noise appeared in the background (about 75%–85% gain).

We applied the appropriate color velocity scale (about 15 cm/sec) by using the kidney program on our US unit. The window (ie, color box) was restricted to the vascular area studied. After visualization of a crossing vessel, pulsed-wave spectral Doppler imaging was performed by using the lowest filter setting (125 Hz) and the smallest scale available that displayed the Doppler waveforms as large as possible without aliasing. Sampling was performed only to differentiate arterial from venous flow signals; there was no attempt to quantify blood flow.

Contrast Material–enhanced CDI.—Our study was approved by the institutional review board, and all patients gave written informed consent before the intravenous administration of the galactose-based, echo-enhancing contrast agent SH U 508A (Levovist). The agent was prepared in a standard manner and administered in a concentration of 300 mg/mL by means of continuous slow infusion (16) at a rate of 1 mL/min by using a Secura FD perfusor (Braun, Maria Enzersdorf, Austria). Subsequently, color Doppler frequency mode imaging, color Doppler amplitude mode imaging, and pulsed-wave spectral Doppler imaging were performed in the same way that the imaging was performed in the nonenhanced study.

Data Analysis
The data obtained from nonenhanced CDI were compared with those from contrast-enhanced CDI in terms of detection rate and ability to depict crossing vessels at the UPJ. All patients underwent laparoscopic pyeloplasty. The preoperative results obtained at nonenhanced and enhanced color Doppler US were compared with the findings obtained subsequently at laparoscopy.

The collected data were analyzed by using StatView software (version 4.02; Abacus Concepts, Berkeley, Calif). The differences between nonenhanced CDI findings and enhanced CDI findings were evaluated by using the Student t test, the Fisher exact test, and the McNemar test. A P value of less than .05 was considered to be indicative of a statistically significant difference.

	RESULTS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Nonenhanced CDI
The mean time (± SD) to perform the examination was 23 minutes ± 6 (range, 14–35 minutes). Fifteen crossing vessels—14 arteries and one vein—were depicted in 15 (52%) of 29 patients (Table 1). Thirteen vessels were located anteriorly to the UPJ, and two vessels were located posteriorly to the UPJ.

Enhanced CDI
Crossing vessels were considered to be present at enhanced CDI in 22 (76%) of 29 patients; single vessels were depicted in 19 patients, and double vessels (ie, artery and vein) were depicted in three patients (Table 1, Figure). A total of 25 vessels (19 arteries and six veins), including the 15 vessels that had been detected at nonenhanced CDI, were identified at enhanced CDI. Sixteen arteries and five veins were located anteriorly to the UPJ, and three arteries and one vein were located posteriorly to the UPJ. The mean time (± SD) to perform enhanced CDI was 14 minutes ± 4 (range, 7–20 minutes). Thus, the mean examination time was significantly reduced in comparison with that of the nonenhanced study (P < .001). Uniform, subjectively optimal contrast enhancement was achieved during the study with the continuous slow infusion technique (1 mL/min); the administration of up to 15 mL of contrast agent allowed examination times of up to 16 minutes. No substantial clinical side effects from contrast agent administration were observed; two patients complained of a sensation of "heat" at the injection site; however, this disappeared in less than 1 minute.

View larger version (139K): [in this window] [in a new window]   Figure 1a. Crossing artery and vein at the UPJ. (a) Pyelogram obtained in a patient in the supine position 30 minutes after the intravenous injection of a contrast agent demonstrates UPJ obstruction (arrow) with severe hydronephrosis on the right side. b–d, C = lower-pole calyx, P = renal pelvis. (b) Longitudinal nonenhanced CDI scan through the dilated collecting system reveals sparse Doppler signals at the level of the UPJ (arrows), without delineation of a crossing vessel. (c) Longitudinal contrast-enhanced CDI scan shows a marked increase in the color Doppler signals, with depiction of two vessels crossing anteriorly to the UPJ. The artery is indicated by the solid arrows, and the vein is indicated by the open arrow. (d) Findings at laparoscopy confirmed the presence of two anteriorly crossing vessels. A retroperitoneoscopic view, with the kidney, renal pelvis, and ureter tilted anteriorly, is shown. A = artery, P = renal pelvis, U = ureter, V = vein.

View larger version (90K): [in this window] [in a new window]   Figure 1b. Crossing artery and vein at the UPJ. (a) Pyelogram obtained in a patient in the supine position 30 minutes after the intravenous injection of a contrast agent demonstrates UPJ obstruction (arrow) with severe hydronephrosis on the right side. b–d, C = lower-pole calyx, P = renal pelvis. (b) Longitudinal nonenhanced CDI scan through the dilated collecting system reveals sparse Doppler signals at the level of the UPJ (arrows), without delineation of a crossing vessel. (c) Longitudinal contrast-enhanced CDI scan shows a marked increase in the color Doppler signals, with depiction of two vessels crossing anteriorly to the UPJ. The artery is indicated by the solid arrows, and the vein is indicated by the open arrow. (d) Findings at laparoscopy confirmed the presence of two anteriorly crossing vessels. A retroperitoneoscopic view, with the kidney, renal pelvis, and ureter tilted anteriorly, is shown. A = artery, P = renal pelvis, U = ureter, V = vein.

View larger version (99K): [in this window] [in a new window]   Figure 1c. Crossing artery and vein at the UPJ. (a) Pyelogram obtained in a patient in the supine position 30 minutes after the intravenous injection of a contrast agent demonstrates UPJ obstruction (arrow) with severe hydronephrosis on the right side. b–d, C = lower-pole calyx, P = renal pelvis. (b) Longitudinal nonenhanced CDI scan through the dilated collecting system reveals sparse Doppler signals at the level of the UPJ (arrows), without delineation of a crossing vessel. (c) Longitudinal contrast-enhanced CDI scan shows a marked increase in the color Doppler signals, with depiction of two vessels crossing anteriorly to the UPJ. The artery is indicated by the solid arrows, and the vein is indicated by the open arrow. (d) Findings at laparoscopy confirmed the presence of two anteriorly crossing vessels. A retroperitoneoscopic view, with the kidney, renal pelvis, and ureter tilted anteriorly, is shown. A = artery, P = renal pelvis, U = ureter, V = vein.

View larger version (81K): [in this window] [in a new window]   Figure 1d. Crossing artery and vein at the UPJ. (a) Pyelogram obtained in a patient in the supine position 30 minutes after the intravenous injection of a contrast agent demonstrates UPJ obstruction (arrow) with severe hydronephrosis on the right side. b–d, C = lower-pole calyx, P = renal pelvis. (b) Longitudinal nonenhanced CDI scan through the dilated collecting system reveals sparse Doppler signals at the level of the UPJ (arrows), without delineation of a crossing vessel. (c) Longitudinal contrast-enhanced CDI scan shows a marked increase in the color Doppler signals, with depiction of two vessels crossing anteriorly to the UPJ. The artery is indicated by the solid arrows, and the vein is indicated by the open arrow. (d) Findings at laparoscopy confirmed the presence of two anteriorly crossing vessels. A retroperitoneoscopic view, with the kidney, renal pelvis, and ureter tilted anteriorly, is shown. A = artery, P = renal pelvis, U = ureter, V = vein.

All patients underwent laparoscopic UPJ repair; nondismembered pyeloplasty, in which the continuity of the ureter is not interrupted, was performed in anteriorly crossing vessels, because these vessels do not have to be transposed. In cases of a vessel crossing posteriorly to the UPJ, dismembered pyeloplasty, in which the ureter is transected, spaculated, and reanastomosized, was performed to transpose the vessel to the correct anterior position. At laparoscopy, crossing vessels were identified in 23 (79%) of 29 patients. In our series, no vascular complications occurred during the procedures. Accurate measurement of vessel dimension was not possible with CDI, because of blooming of the color signal and the resultant overestimation of the vessel size, or with laparoscopy.

The results of nonenhanced CDI and enhanced CDI compared with the findings of laparoscopy, the standard reference method, in terms of the position (ie, anterior or posterior) and type (ie, artery or vein) of the vessel, are presented in Table 1. The correlation between the number of vessels depicted at nonenhanced and enhanced CDI and the number of vessels identified at laparoscopy is shown in Table 2.

	DISCUSSION

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
The reported success rate of endopyelotomy for relief of UPJ obstruction is 72%–89% (6). Surgical failure is often owing to crossing vessels, and vascular complications have been reported after inadvertent injury to crossing vessels (6,17). These vessels usually arise from lower pole renal arteries that originate from the aorta or renal artery in approximately 6% of all kidneys (18). In patients with obstruction at the UPJ, the percentage of those with crossing vessels has been estimated to be as high as 79% (14), which is similar to the population of patients with crossing vessels in our study.

Crossing vessels are usually located anteriorly to the UPJ, whereas posteriorly crossing vessels are less commonly found (2–5,14). In our series, 21 (81%) of 26 vessels, including three double vessels, were anteriorly positioned, and five (19%) of 26 vessels were posteriorly positioned. Quillin et al (14) reported that the prevalence of posterior crossing vessels influences the reported rate of hemorrhagic complications of endopyelotomy, because the standard posterolateral incision made during endopyelotomy may be inappropriate. In addition, the posterior segmental artery occasionally supplies blood to as much as 50% of the renal parenchyma, and such an injury can be associated with loss of a large portion of functioning renal tissue secondary to infarction (3). No vascular complication was encountered in our patient population by using CDI in the presurgical evaluation of crossing vessels.

The position of the vessels was correctly identified in 22 (96%) of 23 patients by means of contrast-enhanced CDI. One small vein located posteriorly to the UPJ was a false-negative finding at CDI with contrast agent enhancement. Hence, contrast-enhanced CDI may permit safer reparative triage: Patients with crossing vessels should undergo laparoscopic repair, whereas the others may be treated with endopyelotomy.

All of the patients enrolled in our study underwent laparoscopic pyeloplasty, at which time crossing vessels were identified in 23 of the 29 patients. Nonenhanced CDI depicted 15 of the 23 surgically confirmed cases of crossing vessels; this resulted in a sensitivity of 65% and an overall accuracy of 72% for vessel detection. Enhanced CDI enabled confirmation of 22 of 23 patients with crossing vessels and excluded six of six patients suspected of having crossing vessels; this resulted in a sensitivity of 96% and an overall accuracy of 97%. The sensitivity of the detection of veins in particular markedly increased after contrast agent administration, from 14% (one of seven veins) to 86% (six of seven veins) (P < .05, Fisher exact test). Without the use of the US contrast agent, seven patients with vessels crossing at the UPJ would have been missed. Thus, the rate of detecting crossing vessels improved significantly with use of the US contrast agent (P < .016, McNemar test).

CDI has the benefit of being a nonradiating, noninvasive, and relatively inexpensive imaging modality. The poor depiction rates observed with slow flow and with flow within small vessels can be compensated for by using contrast agent enhancement (19–21). In our study, the contrast agent was shown to improve the detection of crossing vessels at the UPJ, especially in veins and smaller arteries. In addition, the agent was able to help halve the time required for the examination (P < .001). Our use of the continuous slow flow infusion technique (16) also allowed examination times of up to 16 minutes, with uniform, subjectively optimal enhancement. In comparison, contrast-enhanced Doppler imaging with the bolus technique is limited to about 4 minutes (22). In our series, no important clinical side effects from the agent were noted.

Admittedly, having all of the color Doppler examinations performed by a single operator is a limiting factor in that no data on intraobserver or interobserver variability are provided. A further drawback of our Doppler imaging study was that, in the initial phase, it was quite time-consuming; however, once we had overcome the initial learning phase, the time required for the examinations was considerably reduced.

In conclusion, CDI is highly accurate in depicting crossing vessels at the UPJ. A comparison between the prospective results of CDI and the subsequent findings of laparoscopy, the reference-standard method, showed excellent agreement. The study should first be performed with nonenhanced Doppler imaging, and if vessels are detected, no further work is needed. If no vessels are found, CDI with contrast agent enhancement should then be performed. In this way, CDI aided by an intravenously administered contrast agent can provide useful presurgical information by enabling the identification of crossing vessels and potentially decrease the prevalence of vascular complications at endopyelotomy.

	Acknowledgments

 
The authors thank Archie A. Alexander for assisting with the preparation of this manuscript.

	Footnotes

 
Address reprint requests to F.F.

Abbreviations: CDI = color Doppler imaging UPJ = ureteropelvic junction

Author contributions: Guarantors of integrity of entire study, F.F., G.J., G.B., D.z.N.; study concepts and design, F.F., G.J.; definition of intellectual content, F.F., G.J., G.B., D.z.N.; literature research, H.S.; clinical studies, F.F., G.J.; data acquisition, F.F., H.S.; data analysis, F.F., G.H.; statistical analysis, F.F., G.H.; manuscript preparation and review, F.F., G.J.; manuscript editing, F.F.

Received May 6, 1998; revision requested July 10, 1998; revision received September 2, 1998; accepted October 6, 1998.

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TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 

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