Best Stent Length Predicted by Simple CT Measurement Rather than Patient Height

Abstract

Introduction and Objectives:

Ureteral stent length is important, as stents that are too long might worsen symptoms and too short are at higher risk of migration. The purpose of this study was to determine if patient or radiologic parameters correlate with directly measured ureteral length and if directly measured ureteral length predicts proper stent positioning.

Methods:

During stent placement, ureteral length (ureteropelvic junction to ureterovesical junction distance) was directly measured by endoscopically viewing a ureteral catheter (with 1-cm marking) emanating from the ureteral orifice. A 22, 24, or 26 cm stent was chosen to be closest to the measured ureteral length. For ureters >26 cm, a 26 cm stent was chosen. Ends of an “ideally positioned” stent were fully curled in the renal pelvis and bladder, without crossing the bladder midline. Rates of ideal stent position were compared between patients with matching stent and ureteral lengths and those with stent lengths differing by ≥1 cm (mismatched). The measured ureteral length was correlated with patient height, L1–L5 height, and length measured on CT.

Results:

Fifty-nine ureters from 57 patients were included. Height was reasonably correlated with L1–L5 height (Spearman correlation coefficient [rho] = 0.79), although both were poorly correlated with directly measured ureteral length (rho = 0.18 for height and 0.32 for lumbar height). Ureteral lengths measured on CT correlated well with direct measurement (rho = 0.63 for axial cuts and rho = 0.64 for coronal cuts). Matched stent length was associated with higher rates of ideal stent position than mismatched (100% vs 70.9%, p = 0.006).

Conclusions:

CT measurements, rather than height, correlate well with measured length and could be used to choose the appropriate stent length. Stents matching directly measured ureteral lengths are associated with high rates of ideal stent position.

Introduction

Ureteral stents are an integral part of urologic surgery. Stents are commonly used to relieve ureteral obstruction, or are placed following urologic procedures such as ureteroscopy, endoureterotomy, and pyeloplasty. Double-J stents are made of soft polymers and are commercially available in a variety of diameters and lengths. Unfortunately, up to 80% of stented patients experience pain and/or lower urinary tract symptoms (LUTS), resulting in a significantly decreased quality of life (QoL).^1

–5 Choosing the appropriate length of stent is of great importance. A stent that is too long may increase the risk of stent-related symptoms, particularly if the distal coil crosses the bladder midline,^4
–6 while one that is too short may be at higher risk for proximal migration.⁷

Direct ureteral measurement using graduated catheter is the gold standard for determining ureteral length, but may be time-consuming and may require repeat instrumentation. The optimal indirect method for determining ureteral length, and subsequently the ideal length of stent, has not been identified. Patient height has been used to guide the choice of stent length, with taller patients receiving longer stents. However, the accuracy of this method has been questioned.^8

–11

The primary objective of this study was to determine the correlations between direct intraoperative ureteral measurement and indirect estimators of ureteral length, including patient height, ureteral length as measured on preoperative CT, and lumbar vertebral height. The secondary objective was to determine whether stents matching ureteral length have higher rates of ideal stent positioning.

Materials and Methods

Research ethics board approval was obtained for a prospective study of patients undergoing ureteroscopy at a single institution between September 2011 and March 2013. Only patients with a preoperative CT were included.

Direct measurement of ureteral length measured directly using a graduated catheter (UL_cath) was performed using a graduated 5F ureteral catheter with markings at 1 cm intervals. The catheter was fluoroscopically positioned at the ureteropelvic junction (UPJ), and the length of the ureter was measured by endoscopically viewing the catheter marker emanating from the ureteral orifice.

In addition, ureteral length was measured on CT using both the axial (UL_ax) and coronal (UL_cor) reconstructions. UL_ax was determined by multiplying the number of slices between the UPJ and ureterovesical junction (UVJ) by slice thickness. The UPJ was defined as the slice where caliber of the renal pelvis narrowed to match the caliber of the proximal ureter, and the UVJ was defined as the slice where the distal ureter could be seen entering the bladder wall. UL_cor was determined by measuring the straight linear distance between the UPJ and UVJ on the coronal reconstruction. Lumbar vertebral height (L1–L5) was measured vertically on the CT scout radiograph. All of these measurements were made preoperatively, effectively blinding the assessor to the directly measured length.

Placement of a 22, 24, or 26 cm 6F Double-J stent (Cook Urological, Bloomington, IN) was performed, with stent length chosen based on the directly measured length of the ureter (UL_cath). Where UL_cath was between available stent lengths, the length was rounded up to the closest available length. For example, in a ureter measuring 25 cm, a 26 cm stent would be placed. In ureters longer than 26 cm, the longest stent (26 cm) was used.

Mean ureteral length was compared across sides and gender using the Student's t-test. To determine the best surrogate measurement for the true measured UL_cath, Spearman correlation was utilized to assess for a statistical dependence between UL_cath and patient height, lumbar vertebral height (L1–L5, measured on CT), UL_ax, and UL_cor. To examine the effect of stent length on ideal stent positioning, each stent was classified as “matched” or “unmatched.” A stent was “matched” if stent length exactly matched UL_cath (i.e., UL_cath of 22, 24, or 26); all others were “unmatched.” Evaluation of stent positioning was performed on a plain abdominal x-ray (KUB) at the first postoperative visit, before stent removal. A stent was considered ideally positioned if the proximal end was fully curled and in the renal pelvis and the distal end was fully curled in the bladder and did not cross midline. The rate of ideal stent position was compared between the matched and unmatched stent groups using the chi-square test. All analyses were performed with use of SAS software version 9.2 (SAS Institute, Inc., Cary, NC). A p-value <0.05 was considered significant.

Results

Seventy-three ureters in 70 patients were included in the study. Fifty (68.5%) were in males and 23 (31.5%) were in females. Thirty-three (45.2%) were right-sided ureters and 40 (54.8%) were left. Mean age was 55.9 ± 13.4 years. The ureteral lengths did not differ significantly between sides (25.1 ± 2.5 cm on right, 24.3 ± 2.5 cm on left, p = 0.160) or genders (24.4 ± 2.5 cm in males, 25.2 ± 2.5 cm in females, p = 0.243).

UL_cath correlated poorly with patient height (rho = 0.30), but moderately well with ureteral length measured on both axial CT images (rho = 0.63) and coronal CT images (rho = 0.64). Lumbar vertebral height demonstrated moderate correlation with patient height (rho = 0.76) but poor correlation with UL_cath (rho = 0.31; Table 1).

Table 1.

Spearman Correlation Coefficients (Rho) Between Measurements

	UL_cath	Patient height	Lumbar vertebral height	UL_ax	UL_cor
UL_cath	1.00	0.30	0.31	0.63	0.64
Patient height	0.30	1.00	0.76	0.33	0.36
Lumbar vertebral height	0.31	0.76	1.00	0.37	0.36
UL_ax	0.63	0.33	0.37	1.00	0.89
UL_cor	0.64	0.36	0.36	0.89	1.00

rho ≥0.8 denotes a strong correlation, 0.5 < rho <0.8 denotes a moderate correlation, and rho ≤0.5 denotes a weak correlation.

UL_ax = ureteral length measured on axial CT; UL_cath = ureteral length measured directly using graduated catheter; UL_cor = ureteral length measured on coronal CT.

In ureters with matched stent length, the rate of ideal stent positioning was higher than in unmatched stents: 100% of matched stents (n = 18) were ideally positioned vs only 70.9% in unmatched stents (n = 55, p = 0.006). Twelve of the 16 stents of nonideal length were longer than the ureteral length measured by a catheter. All but one of these were found to be nonideal due to excessively long stent length, with eight having a proximal coil outside the renal pelvis (in a calix) and three crossing the bladder midline. One stent longer than the catheter measured length was found to be too short, with only a partial distal coil. Four stents of nonideal length were shorter than the ureteral length measured by a catheter. Three of these were found to be excessively short, with two having only partial distal curls and one a partial proximal curl. One stent shorter than the catheter measured ureteral length was found to be too long, with a proximal coil in the calix. In the unmatched group, the magnitude of stent length difference was 1.4 ± 0.7 cm for ideally positioned stents compared with 1.6 ± 1.0 cm for nonideally positioned stents (p = 0.407).

Discussion

Ureteral stents are used to maintain ureteral patency, either in the face of a primary cause of obstruction, or for secondary prevention following procedures such as ureteroscopy. Although their role is well recognized, it is also clear that ureteral stents are associated with significant morbidity. Joshi and colleagues developed and validated the Ureteral Stent Symptom Questionnaire (USSQ) to better quantify the frequency and magnitude of stent-related symptoms and their impact on QoL.¹ Subsequent studies using the USSQ or similar questionnaires have identified rates of LUTS and pain of up to 80%.^2

–5,12

Efforts to determine predictors of stent-related symptoms have identified the amount of stent material in the bladder (in particular when the coil crosses the bladder midline),^2,4
–6,13 proximal coil positioned in an upper pole calix,⁶ stent duration,⁶ and stent material and construction¹⁴ as contributors. Of these, a distal coil crossing the bladder midline is the most consistent finding associated with stent-related symptoms. It is possible that a stent of ideal length and position (i.e., of a length matching the length of the ureter, with full coils in the renal pelvis and urinary bladder, but without the distal coil crossing the bladder midline) may result in decreased rates and severity of stent-related symptoms.

The true length of the ureter must be known to select the ideal length of stent for an individual patient. Although direct measurement of ureteral length intraoperatively is a viable option, a more ideal tool would be a noninvasive, quick, and easy preoperative predictor of a ureteral length. Preoperative prediction would theoretically help to shorten the intraoperative time and for the proper stent to be readily available.

Various predictors of ureteral length have been proposed, with patient height being the most frequently used in daily practice. However, multiple recent studies have identified a poor correlation between patient height and ureteral length.^8

–11,15 This study also found that patient height was poorly correlated with directly measured ureteral length (rho = 0.30), further supporting height as a poor predictor of ureteral length. Lumbar vertebral height on CT scout was found to be well correlated with patient height (rho = 0.76), but poorly correlated with UL_cath (rho = 0.31). This metric was chosen as a potentially more reliable and accurate variable than patient height, and while lumbar height may be used to as an alternative measure of patient height, neither is useful in the estimation of ureteral length.

Several studies have examined the role of preoperative intravenous urogram (IVU) in the determination of ureteral length.^10,11,15 Statistically significant correlations between the straight linear distance between the UPJ and UVJ, as well as the length of the ureteral trace, and ureteral length have been suggested.^10,11 When Kawahara and coworkers compared multiple different measurements on IVP with directly measured ureteral length, they found only a moderate correlation, which was inferior to that of CT measurements.¹⁵ Furthermore, IVP is no longer a common form of imaging. Adopting preoperative IVP as a method of estimating ureteral length would therefore require additional imaging, making it expensive and impractical.

The majority of patients with conditions requiring ureteroscopy present with a preoperative CT. This makes CT measurement of ureteral length an attractive option, as it would allow for advance knowledge of the appropriate length of stent, and not impact on operative time. Kawahara and coworkers found that the distance between the renal vein and UVJ as measured on axial cuts was moderately correlated with directly measured ureteral length (r = 0.617), and was superior to patient height and IVP measurements in the estimation of actual ureteral length.¹⁵ This study compared both axial and coronal CT measurements to directly measured ureteral length. Both were found to be moderately correlated with directly measured ureteral length (UL_ax r = 0.63, UL_cor r = 0.64). This is similar to the degree of correlation found by Kawahara and coworkers; Shrewsberry and coworkers compared the distance between the UPJ and UVJ on axial CT cuts plus a 20% correction to directly measured ureteral length in men undergoing treatment for stone disease. This corrected measurement was found to be well correlated with directly measured length (r = 0.979).⁹

There is no universally agreed upon measure of “ideal” stent length or placement. However, a full proximal coil in the renal pelvis and a full distal coil in the bladder, but not crossing the midline, are components of what constitutes ideal stent length and placement.^7,10,16,17 This study classified a stent as ideally sized and placed when it met all three of these criteria. Stents with only partial coils or proximal migration were considered excessively short, while those with proximal coils in calices or distal coils crossing bladder midline were considered excessively long. Stents of a length that exactly matched the directly measured ureteral length were found to be of ideal length in 100% of cases, while those that did not exactly match were ideal only 70.9% of the time (p = 0.006). These results indicate that the accurate determination of ureteral length results in an increased rate of ideal stent length and placement. Furthermore, the majority (12 of 16) of the stents of nonideal length were excessively long. Given the recognized relationship between excessively long stents and increased rates of stent-related symptoms, it is possible that more accurate determination of appropriate stent length may decrease patient morbidity.

The main limitation of this study is that stent-related symptoms were not assessed through the use of a tool such as the USSQ. As such, no direct conclusions can be drawn regarding the effect of ideal stent placement on stent-related symptoms in this study. However, the existing literature would suggest that the characteristics that would qualify a stent as nonideal in this study are also consistently associated with increased stent symptoms. The further evaluation of stents chosen based on indirect measurements would benefit from the formal evaluation of stent-related symptoms.

Conclusions

CT measurements, rather than patient height, correlate well with directly measured ureteral length and could be used to choose appropriate stent length. Stents of a length matching directly measured ureteral length are associated with high rates of ideal stent position.

Footnotes

Acknowledgment

Daniela Ghiculete, Research Coordinator, St. Michael's Hospital, University of Toronto (Toronto, Canada).

Author Disclosure Statement

K.T.P.: Boston Scientific Corporation (Consultant/Advisor/Meeting Participant/Lecturer), Paladin Labs (Consultant/Advisor), Ferring Canada (Consultant/Advisor), Amgen (Consultant/Advisor), Janssen (Consultant/Advisor), Cook Urological, Inc. (support for Fellowship Program). R.J.D'A.H.: Cook Urological, Inc. (support for Fellowship Program), Cook Medical (Royalty agreement). The remaining authors have no competing financial interests.

Abbreviations Used

References

Joshi

, Stainthorpe

, MacDonagh

, et al. Indwelling ureteral stents: Evaluation of symptoms, quality of life and utility. J Urol, 2003; 169:1065–1069.

Calvert

, Wong

, Chitale

, et al. Multi-length or 24 cm ureteric stent? A multicenter randomized comparison of stent-related symptoms using a validated questionnaire. BJU Int, 2012; 111:1099–1104.

Damiano

, Autorino

, De Sio

, et al. Does the size of ureteral stent impact urinary symptoms and quality of life? A prospective randomized study. Eur Urol, 2005; 48:673–678.

Al-Kandari

, Al-Shaiji

, Shaaban

, Ibrahim

, Elshebiny

, Shokeir

. Effects of proximal and distal ends of double-J ureteric stent position on postprocedural symptoms and quality of life: A randomized clinical trial. J Endourol, 2007; 21:698–702.

Giannarini

, Keeley

Jr , Valent

, et al. Predictors of morbidity in patients with indwelling ureteric stents: Results of a prospective study using the validated Ureteric Stent Symptom Questionnaire. BJU Int, 2011; 4:648–654.

El-Nahas

, El-Assmy

, Shoma

, Eraky

, El-Kenawy

, El-Kappany

. Self-retaining ureteral stents: Analysis of factors responsible for patients' discomfort. J Endourol, 2006; 20:33–37.

Kawahara

, Ito

, Terao

, et al. Choosing an appropriate length of loop type ureteral stent using direct ureteral length measurement. Urol Int, 2012; 88:48–53.

Shah

, Kulkarni

. Height does not predict ureteric length. Clin Radiol, 2005; 60:812–814.

Shrewsberry

, Al-Qassab

, Goodman

, et al. A +20% adjustment in the computed tomography measured ureteral length is an accurate predictor of true ureteral length before ureteral stent placement. J Endourol, 2013; 27:1041–1045.

10.

Jeon

, Choi

, Hong

. Determination of ideal stent length for endourologic surgery. J Endourol, 2007; 21:906–910.

11.

Paick

, Park

, Byun

, et al. Direct ureteric length measurement from intravenous pyelography: Does height represent ureteric length?. Urol Res, 2005; 33:199–202.

12.

Joshi

, Stainthorpe

, MacDonagh

, et al. Ureteral stent symptom questionnaire: Development and validation of a multidimensional quality of life measure. J Urol, 2003; 169:1060–1064.

13.

Lingeman

, Preminger

, Goldfischer

, Krambeck

. Assessing the impact of ureteral stent design on patient comfort. J Urol, 2009; 181:2581–2587.

14.

Lee

, Kuskowski

, Premoli

, et al. Randomized evaluation of ureteral stents using validated symptom questionnaire. J Endourol, 2005; 19:990–993.

15.

Kawahara

, Ito

, Terao

, et al. Which is the best method to estimate the actual ureteral length in patients undergoing ureteral stent placement?. Int J Urol, 2012; 19:634–638.

16.

Pilcher

, Patel

. Choosing the correct length of ureteric stent: A formula based on the patient's height compared with direct ureteric measurement. Clin Radiol, 2002; 57:59–62.

17.

, Chen

, Chung

, Lee

, Chen

, Yu

, Huang

. Determining the appropriate length of a double-pigtail ureteral stent by both stent configurations and related symptoms. J Endourol, 2008; 22:1427–1431.