Utility of upper urinary tract video urodynamics in recurrent symptoms and equivocal hydronephrosis after ureteral reconstruction: A retrospective cohort study

To the Editor: Ureteral stricture can lead to dilation of the proximal upper urinary tract and collecting system. Stretching and loading of the ureter by long-term hydronephrosis trigger a stress relaxation effect, which decreases the contractility of the ureter.[1] Morphological changes after surgery may not be obvious even if the obstruction is successfully relieved. Diuretic renography judges split renal function and the nature of obstruction by the uptake and excretion of radionuclides. However, it is influenced by the response of the ipsilateral kidney to diuretics.[2] Currently, there is a lack of homogenized diagnostic and treatment standards, especially evaluation criteria, which makes it difficult to assess the surgical effect and postoperative conditions. Upper urinary tract video urodynamics (UT-VUDS), a perfusion manometry examination, provides information on the pressure changes associated with urine delivery.[3] In this study, we report the clinical application of UT-VUDS in reconstructed ureters with obstinate and equivocal hydronephrosis, and explore their role in long-term therapeutic strategies. From December 2018 to June 2022, a total of 778 consecutive patients underwent upper urinary tract reconstruction in Peking University First Hospital, 202 of whom underwent UT-VUDS, exceeding the required sample size of 77 cases calculated by GPower (Heinrich Heine University Düsseldorf, Germany) (actual power 0.803). We performed a percutaneous nephrostomy regularly before ureteral reconstruction for ureteral rest in complex ureteral strictures, especially long segments or severe strictures. The nephrostomy tube was temporarily retained as protective drainage after surgery and was closed 1–2 weeks after surgery. The indication was that the degree of postoperative hydronephrosis did not improve after removal of the ureteral stent. The exclusion criteria included (1) no preplaced nephrostomy tube, (2) contrast agent allergy or intolerance to perfusion, and (3) loss to follow-up. Patients’ baseline characteristics, perioperative results, diuretic renography data, and follow-up data were collected from the Reconstruction of Urinary Tract: Technology, Epidemiology and Result (RECUTTER) database (http://www.3dmi.com.cn/login/pkufh). The hospital ethics committee approved the study protocol (No. 2023-602). Written informed consent was obtained from all patients in the study. UT-VUDS was performed through a preplaced nephrostomy tube if hydronephrosis did not improve [Supplementary Figure 1A–D, https://links.lww.com/CM9/C559]. A double-cava manometry catheter was inserted through the nephrostomy tunnel, and it was connected to a urodynamic system (Medical Measurement Systems, Amsterdam, Netherlands) and a constant flow perfusion device. We prepared another double-cava manometry catheter and inserted it into the bladder, and it was connected to the urodynamic system and urine bag. The patient was placed in the prone position. The contrast medium was diluted to 50% with saline. We defined perfusion into a physiological phase and a high flow phase [Supplementary Figure 1E, https://links.lww.com/CM9/C559]. In the physiological phase, perfusion begins at a rate of 1–3 mL/min. When the renal pelvis and ureter were visualized, we gradually increased the perfusion rate. The pressure was measured simultaneously from the renal pelvis and the bladder. The patient was asked to change position to a sedentary posture if the pressure increased or if the contrast temporarily held up. The termination flow rate was achieved when (1) the patient experienced loin pain, (2) the renal pelvis pressure (RPP) remained elevated without relief, or (3) the perfusion rate reached 20 mL/min. The pressure difference (PD) was calculated by subtracting the bladder pressure from the RPP. The total duration was approximately 10–15 min. The urodynamic results were classified into three types [Supplementary Figure 1F, https://links.lww.com/CM9/C559]. “Normal” (type I): the pressure remains stable near the baseline throughout the perfusion process, and the reconstructed ureter is well visualized. “Borderline” (type II): The RPP increases with perfusion, whereas urography reveals that ureteral peristalsis still occurs. The pressure can decrease to a normal level with peristalsis of the ureter. “Obstructive” (type III): The RPP and PD increase with perfusion and exceed levels. Moreover, ureteral peristalsis can be weak or absent [Supplementary File, https://links.lww.com/CM9/C559]. Patients were monitored every 3 months for symptoms, laboratory examination, and ultrasound. Patients should have at least one postoperative review via contrast enhanced urography/magnetic resonance urography and diuretic renography. Indications for reintervention included no relief of symptoms, aggravation of hydronephrosis, and deterioration of renal function. Statistical analysis was carried out using SPSS (Version 25.0, IBM Corp., Armonk, NY, USA) and GraphPad Prism (Version 7.0, GraphPad Software Inc., San Diego, USA). Normally distributed continuous variables were presented as mean ± standard deviation, non-normally distributed continuous variables were presented as median (minimum–maximum), and categorical variables were presented as frequency and percentage. Chi-squared test was used to test the distribution of category variables. Differences among the subgroups were analyzed using analysis of variance for continuous variables. A receiver-operating characteristic curve was used to evaluate the diagnostic value of UT-VUDS and diuretics renography. A two-sided P value of <0.05 was taken to indicate statistical significance. Among the 202 patients, 101 were male and 101 were female. The mean age was 40.1 ± 13.1 years. The stricture was located on the left side in 103 patients, on the right side in 70 patients, and on both sides in 29 patients. The mean stricture length was 5.9 ± 5.0 cm. The ipsilateral split renal function was 30.3 ± 14.9 mL/min. The baseline characteristics, etiologies, and primary surgeries are listed in Supplementary Table 1, https://links.lww.com/CM9/C559. The median follow-up was 24.1 (9.4–52.1) months. A total of 15 patients required reintervention after the initial operation. The surgical success rate was 92.6% (187/202). All 202 patients successfully completed UT-VUDS. The average perfusion volume was 149.8 ± 64.0 mL. In patients who required reintervention, the median RPP was 44 cm H2O, and the median PD was 24 cm H2O. In the initial failure surgery, 5 patients who had previous balloon dilation required secondary reconstruction, including pyeloplasty (1 patient), pelvic flap ureteroplasty (1 patient), reimplantation (2 patients), and ileal ureter reconstruction (1 patient). Another patient with pyeloplasty underwent balloon dilation. One patient with reimplantation, one patient with pyeloplasty underwent ileal ureter, and one patient underwent secondary ileocalicostomy ureteral substitution. The remaining patients underwent regular replacement of ureteral stents or nephrostomy. In patients without reintervention, the median RPP and PD were 20 and 3 cm H2O, respectively. The cutoff value of the RPP for reintervention was 40 cm H2O (Youden index = 0.474, area under the curve [AUC] = 0.734), and the cutoff value of the PD was 18 cm H2O (Youden index = 0.857, AUC = 0.800). The patients were categorized into three groups: “normal” (type I, 181 cases), “borderline” (type II, 9 cases), and “obstructive” (type III, 12 cases). In particular, 6 out of the 9 patients in the “borderline” group had a large renal pelvis with a median volume of 200 (140–210) mL. In comparison, diuretic renography revealed that 76 patients had poor upper urinary tract drainage, including 35 patients with mechanical obstruction and 41 patients with non-mechanical obstruction. In addition, drainage was unable to be judged in another nine patients because of poor renal function. There was an agreement between the results of the urodynamics and diuretic renography in 73.6% (170/231) of the patients [Supplementary Table 2, https://links.lww.com/CM9/C559]. A receiver-operating characteristic curve was used to evaluate the diagnostic value of UT-VUDS and diuretic renography. The sensitivity and specificity of UT-VUDS for reintervention were 66.7% and 100%, respectively (AUC = 0.833, P <0.001), whereas the sensitivity and specificity of diuretic renography were only 20.0% and 84.5%, respectively (AUC = 0.523, P = 0.769). The trend of creatinine and estimated glomerular filtration rate in patients with different UT-VUDS types during follow-up are shown in Supplementary Figure 1G, H, https://links.lww.com/CM9/C559. The renal function of type I patients was stable. The renal function of type II patients fluctuated, and the change in split renal function was −5.00 ± 0.00 mL/min. The type III patients tended toward an improvement in the ipsilateral glomerular filtration rate (7.72 ± 5.63 mL/min) after the second treatment [Supplementary Table 2, https://links.lww.com/CM9/C559]. This study explores the potential issue of dilation that may still exist after the repair of ureteral stricture.[4] The preliminary results of our center revealed that UT-VUDS helps determine the timing of nephrostomy tube removal and the necessity of secondary intervention. Furthermore, we believe that the standard for the upper urinary tract requiring reintervention after reconstruction can be appropriately relaxed to the points where RPP is greater than 40 cm H2O and the PD is greater than 18 cm H2O. This is different from the standard proposed by Whitaker[3] to define 15 and 22 cm H2O as UT-VUDS. One reason is that the reconstructed upper urinary tract may have pressure fluctuations, and the pressure is affected by the position. In this study, the patients were sometimes asked to change their position to a sedentary posture during the examination, which is closer to the daily condition. Therefore, the hydrostatic pressure needs to be considered. The other reason is the consideration of the pyelovenous backflow, which is likely to occur above renal pressures of 30–35 mmHg.[5] The new standard is below the safety threshold and does not affect renal perfusion and renal function. In this study, we used UT-VUDS to classify patients with postoperative hydronephrosis into three types. All patients with type III underwent reintervention. During the follow-up, the renal function of patients with type III tended to improve. Therefore, we suggest that type III patients with intractable hydronephrosis should receive further treatment. The borderline state after ureteral reconstruction needs attention. Type II patients have insufficient reserve capacity to deal with hydronephrosis. In addition, the large pelvis and calyces volume impose a high load, which makes the reconstructed ureter unbearable.[3] Fortunately, the elevated pressure can be relieved with peristalsis, not to the point where surgery is needed. Therefore, it is important to avoid holding urine or diuretic food and drugs. However, we do not recommend the routine use of UT-VUDS in all patients with hydronephrosis. Because patients who do not undergo preoperative nephrostomy often have mild conditions, routine imaging examinations should be considered first, as imaging urodynamic examinations are invasive for these patients. There are still some shortcomings in this study. The first is the lack of preoperative urodynamic results for comparison. In addition, there is still room for improvement in sample size, particularly in the “borderline” and “obstructive” categories, and retrospective cohorts limit the level of evidence for the findings. Therefore, in the future, it is necessary to carry out a prospective study and compare pre- and postoperative urodynamics to further verify the clinical value and significance of UT-VUDS. In conclusion, persisting dilation after upper urinary tract reconstruction is a confusing condition that cannot be overlooked. The false-positive result of diuretic renography is worrisome. UT-VUDS is suitable for patients with no significant improvement in the degree of hydronephrosis after reconstruction. The UT-VUDS classification helps determine further treatment strategies. The noticeable increase in upper urinary tract pressure and poor contrast agent excretion suggest that the obstruction still exists, and that appropriate intervention should be taken in time. Funding The study is supported by grants from the Peking University Medicine Sailing Program for Young Scholar’s Scientific & Technological Innovation (No. BMU2023YFJHPY013) and National High Level Hospital Clinical Research Funding (Scientific Research Seed Fund of Peking University First Hospital) (No. 2023SF09). Conflicts of interest None.

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