|Year : 2021 | Volume
| Issue : 4 | Page : 177-181
Measuring individual ureteral length using computed tomography urography to determine the appropriate lengths of ureteral stents
Cheng-Han Tsai1, I-Shen Huang2, Wei-Jen Chen3, Wei-Ming Cheng4, Cheng-Yen Chiang5, Wei-Tang Kao6, Eric Yi-Hsiu Huang3, William J Huang2
1 Department of Urology, Taipei Veterans General Hospital, Taipei, Taiwan
2 Department of Urology, Taipei Veterans General Hospital; Department of Physiology; Department of Urology, Shu-Tien Urological Research Center, College of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
3 Department of Urology, Taipei Veterans General Hospital; Department of Urology, Shu-Tien Urological Research Center, College of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
4 Department of Urology, Shu-Tien Urological Research Center, College of Medicine, National Yang Ming Chiao Tung University; Division of Urology, Department of Surgery, Taipei City Hospital Zhongxiao Branch, Taipei, Taiwan
5 Surgical Department, Division of Urology, Taoyuan General Hospital, Ministry of Health and Welfare, Taoyuan, Taiwan
6 Department of Urology, Shuang Ho Hospital, Taipei Medical University; Graduate Institute of Clinical Medicine, Taipei Medical University, New Taipei City, Taiwan
|Date of Submission||28-Apr-2021|
|Date of Decision||07-Jun-2021|
|Date of Acceptance||25-Jun-2021|
|Date of Web Publication||14-Dec-2021|
Dr. I-Shen Huang
Department of Urology, Taipei Veterans General Hospital, No 201, Section 2, Shipai Road, Taipei 112
Source of Support: None, Conflict of Interest: None
Purpose: The purpose of the study was to describe and validate a method for calculating ureteral length using computed tomography (CT) images acquired before ureteral stent placement and to evaluate the appropriateness of fit based on this calculation. Materials and Methods: We analyzed 57 patients who underwent computed tomography urography (CTU). The axial ureteral length (AUL) and coronal ureteral length (CUL) were derived from measurements made on the CTU images, and the length of each patient-specific ureteral stent was chosen based on the calculated ureteral length. Results: Overall, 105 ureters were measured: 54 (51.4%) right side and 51 (48.6%) left side ureters. The mean CUL and AUL of right ureters were 22.5 ± 2.3 cm and 22.5 ± 2.3 cm, respectively, whereas the mean CUL and AUL of left ureters were 23.6 ± 2.2 cm and 23.4 ± 2.1 cm, respectively. Pearson correlation analysis showed that body height was significantly correlated with ureteric length (right CUL and patient height: r =0.441, P = 0.001; right AUL and patient height: R = 0.445, P = 0.001; left CUL: R = 0.341, P = 0.029; left AUL: R = 0.339, P = 0.015). Thirteen of 57 patients underwent ureteral stent insertion; none experienced stent migration (upward or downward) before the removal of the ureteral stent. Comparison of proposed stent size with actual stent size in the 13 patients shows the percentage of size appropriateness (as defined by concordance between proposed and actual stent length) to be 76.9% (10/13). Conclusion: The patient's height was found to correlate significantly with CT-derived measurements of ureteral length. Accordingly, the choice of ureteral stent length can be reliably decided from CT measurements.
Keywords: Body height, computed tomography, ureteral catheters, ureteral length
|How to cite this article:|
Tsai CH, Huang IS, Chen WJ, Cheng WM, Chiang CY, Kao WT, Huang EY, Huang WJ. Measuring individual ureteral length using computed tomography urography to determine the appropriate lengths of ureteral stents. Urol Sci 2021;32:177-81
|How to cite this URL:|
Tsai CH, Huang IS, Chen WJ, Cheng WM, Chiang CY, Kao WT, Huang EY, Huang WJ. Measuring individual ureteral length using computed tomography urography to determine the appropriate lengths of ureteral stents. Urol Sci [serial online] 2021 [cited 2022 May 21];32:177-81. Available from: https://www.e-urol-sci.com/text.asp?2021/32/4/177/332412
| Introduction|| |
Ever since the ureteral stent was first described in 1967, it has been widely used clinically for indications including the management of hydronephrosis caused by ureteral obstruction, preventing ureteral stricture postureteral surgery, or facilitating urine drainage after a ureteroscopic surgery. Although properly placed stents can maintain the patency of the ureter, they could also be undesirably associated with hematuria, urinary tract infection, low back soreness, urinary frequency, urgency, or urinary incontinence, which all negatively impact patients' quality of life., It is widely accepted that choosing the optimal length of a ureteral stent may reduce comorbidities and minimize the risk of stent migration. Particularly, choosing a stent that is either too long or too short for the patient could result in upward or downward migration, even when a double-coil design is utilized to properly anchor the stent. Stent migration could lead to exaggerating symptoms, which may require stent replacement or ureteroscopic retraction.
Prediction of ureteral length before stent insertion by a urologist is commonly based on the patients' height; however, a lack of correlation between the height and length of the ureter has been reported in the previous literature.,, Various other methods have also been introduced to predict ureteral length indirectly including measurement of the distance from the ureteral pelvic junction (UPJ) to the ureterovesical junction (UVJ), measurement of the distance from mid-kidney to UVJ, and calculating the number of slices between UPJ and UVJ and multiplying by image thickness of computed tomography (CT), followed by a + 20% adjustment.
Although ureteral length estimation can be achieved by direct measurement with a guidewire or ureteral stent, the accuracy of such measurement has been questioned because of the possible “bunching up” effect of the redundant ureter. Furthermore, because of concerns with excessive radiation exposure and operative time, direct intraoperative measurement of ureteral length has not been universally adopted in routine practice.
Herein, a method for calculating ureteral length using CT images acquired before ureteral stent placement has been described and validated, and the appropriateness of fit was further evaluated on the basis of these calculations.
| Materials and Methods|| |
During the period between January 2016 and December 2016, 57 patients who underwent computed tomography urography (CTU) and received a diagnosis of upper urinary tract urothelial carcinoma, urinary bladder urothelial carcinoma, cervical cancer, kidney complicated cyst, or urolithiasis have been analyzed. A total of 105 ureters were assessed through CTU exam. The study was conducted according to the approval of the Taipei Veterans General Hospital Institutional Review Board protocol (IRB number: 2020-04-002BC). The patient consent was waived by the IRB.
All patients in the study received the three-phase CTU by 16 multiple detector CT scans (Somatom Sensation 16, Siemens Healthcare). The three-phase CTU protocols are triphasic examinations that include unenhanced imaging from the kidney to the bladder, a corticomedullary phase, and a nephrographic phase. The images from the latter two phases were acquired 30 and 90 s, respectively, after the administration of 100 ml iopamidol (Iopamiro 370 mg I/mL; Bracco, Italy) at a rate of 2 mL/s. The slice thickness of the axial and coronal images was 5 mm.
The axial ureteral length (AUL) was measured by tracing the ureteral trace in the CT axial reconstruction images from UPJ to UVJ. The UPJ slice was identified as the image shown in the CT slice, wherein the upper ureter appeared in continuity with the renal pelvis, and the UVJ slice was identified as the cut visualizing the joining of the distal ureter into the bladder. The center point of the ureteral trace at every axial CT slice was marked, and the distance between the consecutive ureteral center marks was measured. The minimal distance between the two consecutive center points was assigned a value of 5 mm if the measurement was <5 mm, because of the given slice thickness. The individual distances between cuts were added up to obtain the measured AUL. The coronal ureteral length (CUL) was calculated as the sum of ureteral lengths measured from an individual coronal slice, with the minimum assignment of 5 mm, again accounting for slice thickness. Ureteral stent length was chosen on the basis of the resulting calculated ureteral length (i.e., 22 cm stent for the ureteral length of <22 cm; 24 cm stent for ureteral lengths of >22 and <24 cm).
Patient characteristics were represented as n (%) or the mean ± standard deviation. The Pearson correlation coefficient was used to evaluate the strength of association between body height and ureteric length. All statistical analyses were conducted using SPSS Statistics version 22 (IBM Corp, Armonk, NY, USA), assuming a two-sided test with a 5% level of significance (P < 0.05).
| Results|| |
The mean age of the 57 patients included in the study was 65.9 ± 13.1 years, the mean body surface area was 1.67 ± 0.17 m2, and the mean body height was 160.7 ± 7.9 cm. Of these patients, 31 (54.4%) were male and 26 (45.6%) were female. A total of 105 ureters were measured, and as regards laterality, 54 (51.4%) were right side ureters and 51 (48.6%) were left side ureters. [Table 1] presents the demographic characteristics, which shows three patients (5.1%) with the extrarenal pelvis, five (8.6%) with urolithiasis, three (5.2%) with hydronephrosis, 16 (27.6%) with a history of bladder cancer, and 16 (27.6%) with a history of upper tract urothelial carcinoma. Other etiologies include hematuria, extrarenal pelvis, cervical cancer, endometriosis, and prostate cancer [Table 1].
|Table 1: Demographic data of patients receiving computed tomography urography for ureteral length measurement|
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The Pearson correlation analysis showed that body height was significantly correlated with ureteric length (right CUL and patient height: R = 0.441, P = 0.001; right AUL and patient height: R = 0.445, P = 0.001; left CUL: R = 0.341, P = 0.029; and left AUL, r = 0.339, P = 0.015). The mean CUL and AUL of the right ureters were 22.5 ± 2.3 cm and 22.2 ± 2.0 cm, respectively, whereas the mean CUL and AUL of the left ureters were 23.6 ± 2.2 cm and 23.4 ± 2.1 cm, respectively. In the subgroup analysis, our patients were categorized into four groups according to body height: 146–155 cm, 156–165 cm, 166–175 cm, and >175 cm. In the 146–155 cm group, the mean CUL and AUL of the right ureters were 21.3 ± 2.0 cm and 21.1 ± 2.1 cm, respectively, and the mean CUL and AUL of the left ureters were 23.1 ± 2.0 cm and 22.9 ± 1.9 cm, respectively. In the 156–165 cm group, the mean CUL and AUL of the right ureters were 22.7 ± 1.8 cm and 22.5 ± 1.6 cm, respectively, whereas the mean CUL and AUL of the left ureters were 23.5 ± 1.6 cm and 23.3 ± 1.8 cm, respectively. In the 166–175 cm group, the mean CUL and AUL of the right ureters were 23.5 ± 2.9 cm and 23.3 ± 2.2 cm, respectively, whereas the mean CUL and AUL of the left ureters were 22.7 ± 1.8 cm and 23.2 ± 1.9 cm, respectively. Finally, for individuals with a height of >175 cm, the mean CUL and AUL of the right ureters were 23.6 ± 0.9 cm and 23.7 ± 1.2 cm, respectively, whereas the mean CUL and AUL of the left ureters were 25.6 ± 1.5 cm and 25.5 ± 1.5 cm, respectively [Table 2].
Of the 58 patients, 13 underwent ureteral stent insertion using the same stent material (silicone) and stent diameter (6 Fr). Of the 13 patients, none experienced stent migration (upward or downward) before ureteral stent removal. In one patient, a distal loop across the midline was observed after stent insertion. [Table 3] presents the proposed ureteric stent length according to body height and laterality, and a comparison of the proposed stent size with actual stent size in the 13 patients shows the percentage of size appropriateness (as defined by concordance between proposed and actual stent length) to be 76.9% (10/13) [Figure 1].
|Table 3: Proposed ureteric stent length according to body height and laterality (right/left)|
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|Figure 1: Size appropriateness (defined by concordance between proposed and actual stent length) in patients receiving ureteric stent insertion|
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| Discussion|| |
This study evaluated the calculation of individual ureteral lengths using CTU to determine the appropriate length of ureteral stent placements, which is an issue that confronts urologists every day. Considering stent-related complications including stent migration or stent-related symptoms (including lower urinary tract symptoms), accurately predicting the individual ureteral length is crucial for appropriate ureteral stent length adoption.
According to the previous reports, several methods have been used to determine the ureteral length. Theoretically, direct measurement of the ureteral length can be achieved using guidewire or ureteral catheter intraoperatively. However, these techniques may be inaccurate and time consuming and will certainly result in increased radiation exposure; thus, they are rarely performed in routine clinical practice. Particularly, based on a previous study conducted by Pilcher and Patel, direct ureter measurement using the guidewire technique tends to overestimate stent size, mainly because a ureteral stent helps straighten the circuitous ureteral curve, causing the ureters to shorten. Kawahara et al. have demonstrated that choosing a loop ureteral stent having the same length as, or 1 cm less than that of the ureter is associated with a 2.9% risk of migration and an 8.6% risk of having an excessive length when the proximal end of the ureteral stent was placed in the renal pelvis. Conversely, stent migration rates of 20% are expected if the proximal end was anchored in the upper calyx with an indwelled ureteral stent that is 1 cm less than the ureteral length. These factors make choosing the optimal length for a ureteral stent challenging.
To obviate the need for direct ureteric length estimation, numerous studies have investigated the use of noninvasive assessment techniques including CT scan. Kawahara et al. have analyzed urolithiasis patients and have reported that the distance from the renal vein to the UVJ estimated by noncontrast axial CT highly correlated with the actual ureteral length (r = 0.617), as compared with assessments using intravenous urography or patient height. Moreover, Shrewsberry et al. have suggested applying a 20% adjustment to axial CT measurements to account for the ureteral curvature, and this was shown to provide the highest accuracy (r = 0.979) from direct measurement.
Body height is an assessment tool commonly used in research and clinical practice. This is in part because CT imaging is not always available on a per-patient basis before ureteral stenting, which leaves body height as the only substitute for ureteral length estimation. However, using body height to predict the ideal ureteral stent length has yielded conflicting results. Pilcher and Patel et al. have demonstrated that patient height was a more reliable guide to ureteric stent length than direct ureteric measurement, which oversized the stent by 83%. By contrast, several other studies have failed to uncover such a high correlation.,, A possible explanation for these contradictory results is that the aforementioned studies do not account for ureter laterality, i.e., whether it is on the right or left side. In fact, the right ureter is significantly shorter than the left ureter, by 1 cm, and this is typically due to the relative caudal position of the right kidney. Accordingly, studies that fail to distinguish between right ureters from tall individuals and left ureters from less tall individuals would introduce an inherent theoretical uncertainty into the results, thereby masking any significant association between height and ureteral length. In our study, bilateral ureter lengths were explicitly noted and were compared with body height separately, and indeed such a significant correlation was discovered.
Previous studies postulated that there is a wider range of variation in body heights than in actual ureteral lengths between individuals.,, Patients within a certain range of body heights may have a similar ureteral length. Therefore, a better prediction of ureteral length might be obtained by categorizing an individual's body height as lying within a certain range, and subsequently analyzing his/her body height as a categorical parameter, rather than treating the heights and lengths as continuous parameters. Pilcher and Patel have first reported that using 22 cm ureteral stent for a body height of <178 cm, 24 cm for a body height of 178–193 cm, and 26 cm for a body height of >193 cm correctly predicted ureteral stent lengths in 61% of ureters assessed. For the Asian population, Ho et al. have recommended a 22 cm stent length for patients with height <175 cm and have reported no incidence of stent migration, with similar results being reported by Lee et al.
In this study, the ureteral length has been calculated using CTU images in 57 patients, and their correlation with body height has been analyzed. Unlike previous research studies, which mainly investigated ureteral length in urolithiasis patients, the etiologies of our patient cohort include extrarenal pelvis, urolithiasis, bladder cancer, cervical cancer, and upper urinary tract urothelial carcinoma cases, meaning our data of ureteral length can be applied clinically to a wider range of patients. In addition, the ureteral length was measured using CTU in all patients, which allows a more accurate calculation of ureteral length than noncontrast CT scan only. On the basis of the measurements, our patients were categorized into four groups according to their body height, and body height was found to be correlated significantly with both AUL (r = 0.445 at the right side and r = 0.339 at the left side) and CUL (r = 0.441 at the right side and r = 0.341 at the left side). Previous studies reported that a 22 cm-long ureteral stent was appropriate for patients with a height of <175 cm in Chinese and Korean populations. However, based on the results of our study, a 24 cm stent is more appropriate for individuals with different heights.
This study has a few limitations that should be noted. The first limitation is the small number of cases. Moreover, although patients with various etiologies have been included, with a small number and various characteristics of our patients, the data of ureteral length may not be well applied to individual patients with unique etiology. Second, the estimated ureteral length was based on calculations based on CT scans – actual ureteral length was not intraoperatively measured. They may therefore be subject to biases and confounding by manual computation. Furthermore, if a patient did not receive CTU for evaluation, the regular CTU measuring ureteral length may not be feasible. Third, despite the Pearson correlation analysis showing that body height significantly correlated with ureteric length (P < 0.05), with r value around 0.339–0.445, it indicates that body height and ureteric length are not strongly positively correlated. Finally, a small proportion of the individuals received ureteral stenting in our cohort, whereas the adoption of ureteral stent size based on CT measurement is concordant in 76.9% of cases to our proposed size regarding height and laterality. The concordance can translate into judging the length of the JJ probe for an individual corresponding to one's height and laterality.
| Conclusion|| |
The patient's height was found to correlate significantly with CT-derived measurements of the ureteral length. Accordingly, the choice of ureteral stent length can be reliably decided from CT measurements.
Financial support and sponsorship
Conflicts of interest
Prof. William J. Huang, an editorial board member at Urological Science, had no role in the peer review process of or decision to publish this article. The other authors declared no conflicts of interest in writing this paper.
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[Table 1], [Table 2], [Table 3]