Fluoroscopy-free semirigid ureteroscopy for ureteral stone treatment: A prospective single-arm study of feasibility, efficacy, and safety

Abstract

Objectives:

Patients with urolithiasis receive a significant amount of radiation during diagnosis, treatment, and follow-up of their pathology, with nearly 20% receiving more than the annual recommended, creating a growing concern regarding radiation exposure faced by patients and health personnel. The objectives of the study were to describe a standardized fluoroscopy-free (FF) semirigid (SR) ureteroscopy (URS) technique for ureteral stone treatment and to determine the feasibility, efficacy, and safety of this technique for the treatment of ureteral stones comparing it to a historical cohort of fluoroscopy-guided (FG) SR-URS.

Materials and Methods:

A prospective single-arm study of patients submitted to FF SR-URS was conducted. Visual and tactile cues were employed to avoid the use of ionizing radiation. The success (feasibility), stone-free (efficacy), and complication (safety) rates of each procedure were registered. The results were compared to a historical cohort of patients that underwent FG SR-URS at our center.

Results:

One hundred and five patients subjected to FF SR-URS were included in the study and compared to a historical cohort of 87 patients subjected to FG SR-URS. The main characteristics were comparable among groups. Ninety-seven patients (92.38%) were completed without any use of ionizing radiation. The stone-free rate was 92.45%, similar to the historical cohort. Only Clavien I and II complications were found without statistical difference between the study groups. The average dose of radiation exposure for the historical cohort was approximately 0.5 mSv.

Conclusions:

FF SR-URS is a feasible, efficacious, and safe technique for treating the ureteral stones for urologists with good practice of the traditional technique. Implementing this procedure allows a decrease in radiation exposure to both patients and health personnel.

INTRODUCTION

Urolithiasis is a frequent and growing public health problem. In 1994, data from The National Health and Nutrition Examination Survey (NHANES) observed a prevalence of 6.4% in men and 4.1% in women, and 13 years after a new analysis from data NHANES 2007–2010 showed a global prevalence of 8.8% (10.6% in men and 7.1% in women), revealing a 63% increment between both the surveys.[1] Urinary stone disease debuts at a young age (30–50 years old) and is a recurrent disease (40% recurrence rate at 5 years and 75% at 20 years).[2-4] The gold standard for diagnosis and follow-up of patients with the urinary stone disease is nonenhanced computed tomography (CT). This test allows the detection of renal and ureteral calculi from 1 mm, with a sensitivity of approximately 100%.[5] It is estimated that every CT emits between 5 and 10 mGy, the equivalent of an effective dose of 5–10 Msv.[6]

Among the surgical treatment options for ureteral calculi, semirigid ureteroscopy (SR-URS) has become one of the most common procedures.[7] This surgery has dramatically changed the management of ureteral stones and has become the primary treatment option for any distal or mid-ureteral stones, and >10 mm proximal ureteral stones.[5] SR-URS achieves both high stone-free and low complication rates.[8] However, this surgery has been intrinsically linked to the use of ionizing radiation to obtain fluoroscopic images that permit the identification of ureteral stones and adequate placement of guidewires, stents, and ureteroscope localization. Estimates have shown that during a single urinary stone episode, a patient receives on average an effective dose of 29.7 mSv and 20% receive more than 50 mSv, the annual maximum established by the International Commission on Radiological Protection.[9] On the other hand, there is no definition of an inferior limit of radiation exposure under which there is no risk of biological damage.[10,11] Therefore, any exposure to ionizing radiation has the potential to induce malignancy,[12] so efforts to reduce the exposure of patients and health personnel in the operating room are hugely relevant.

Efforts to reduce ionizing radiation exposure during SR-URS have been widely reported. Surgeon use of trigger pedals or the use of pulsed or continuous fluoroscopy has been published.[13,14]

Aiming to reduce the exposure to ionizing radiation by patients and health staff, we prospectively evaluated a protocol of fluoroscopy-free (FF) SR-URS for the treatment of ureteral stones. We assessed the feasibility of the procedure (success rate) by comparing efficacy (stone-free rate) and safety (complication rate) with a historical cohort of fluoroscopy-guided (FG) SR-URS at our institution.

MATERIALS AND METHODS

Patients

Prospective, year-long recruitment of patients that consulted with ureteral stones at a university hospital was performed. One hundred and five patients were included, equivalent to 105 renal units. The surgical treatment consisted of FF SR-URS by two endocrinologists. Patients with anticoagulant treatment, urinary tract malformations, pelvic radiotherapy, previous ureteral stone surgery, and ureteral stenosis were excluded from the study. From a historical database of our center, recruited 1 year before the present study, 87 patients who underwent SR-URS with fluoroscopy were selected and analyzed. The same exclusion criteria were applied.

Objectives

A prospective single-arm study was designed. The primary objective was to evaluate the feasibility of performing FF SR-URS by quantifying the proportion of procedures that were completed with any use of fluoroscopy (successful procedures). As a secondary objective, the efficacy of this surgery was evaluated in terms of stone-free rate, defined as zero fragments or fragments ≤2 mm 1 month after surgery using a nonenhanced CT. The safety of the procedure was evaluated in terms of perioperative complications according to the Clavien–Dindo classification.

Data registration

Demographic and perioperative variables of patients who underwent FF SR-URS were recorded. Age, gender, stone location, laterality and radiological density (Hounsfield units), preoperative double J stenting, presence of hydronephrosis, operating time, use of postoperative double J stent, and complications according to the Clavien–Dindo classification modified for urolithiasis[15] were registered. Causes of procedure failure and conversion to FG SR-URS were recorded.

Identical variables were recorded for a cohort of 87 patients who underwent FG SR-URS at our center. The exposure time to ionizing radiation (seconds) and the effective dose administered to the patient (mSv) were recorded from the data stored in our fluoroscopy machine (C-arm Siemens Arcadis Avantic 36032), which automatically retrieve this information. The results of the two groups were compared.

Fluoroscopy-free semirigid ureteroscopy technique

A standard rigid cystoscopy was performed on all patients. The ureteral meatus of interest was localized, and two 0.035 inches hydrophilic guidewires (Cook Medical, Bloomington, IN, USA) were inserted. If the patient had a ureteral double J stent previously installed, it was used as a guide for the placement of one of the two hydrophilic guidewires. To evaluate the correct ascent of the guidewire to the renal pelvis, the length of male and female genitourinary organs was subtracted to the total length of the guidewire. According to previous reports, ureteral length from the bladder to the ureter-pielic junction was 28 cm in both sexes. Urethra lengths are about 16 cm in males and 4 cm in females.[16,17] We considered an additional 5–10 cm of the distance from ureter-pielic junction to the renal pelvis and also considering the loop of the guidewire inside the pelvis. These lengths (50 cm in men and 40 cm in women) were subtracted to the total length of the guidewire (150 cm). These measures resulted in about 100 cm in males and 110 cm in females of a safety guidewire length outside the urethral meatal orifice [Figure 1].

Figure 1.

(a) Fifteen centimeter mark separations on safety guidewire (separation marks are being used for illustrative purposes only). (b) Male patient with six guidewire marks outside the urethra (about 100 cm)

Tactile cues were used to identify the lithiasis (noting resistance as the guidewire was smoothly ascended/descended through the ureter). The surgeon ascended the guidewires until felt the resistance of the upper calix. A 6°, 41 cm long, and 6.5–8.5 Fr wide SR ureteroscope (Wolf, Germany) was used. The ureteroscope was advanced through the ureteral orifice until the lithiasis was identified. To obtain fragmentation of the calculus, we use a 30-Watt olmium laser with a 550 μm fiber (Sphinx, Lisa Laser, Germany). Stone fragments were extracted from the ureter using a 2.4 Fr Nithinol basket (NCircle, Cook Medical, Bloomington, IN, USA). If deemed necessary, through one of the previously installed guidewires, a 6 Fr ureteral double J stent was installed. The postoperative stent was installed under ureteroscopic vision, and distal stent marks served as a guide to ensure adequate placement of the catheter. Causes of procedure failure and conversion to FG SR-URS were recorded and classified as: excessive resistance during guidewire ascent, nonconcordant guidewire measurements, an unsuccessful ascent of the ureteroscope to the calculus, and suspicion of the unsatisfactory ascent of the double J stent postprocedure.

Statistics

Analysis of the distribution of continuous variables was performed using the Shapiro–Wilk test. Student’s t-test and Mann–Whitney test were used for parametric and nonparametric variables, respectively. For categorical variables, the Chi-squared test was used. Statistical significance was defined as P < 0.05.

RESULTS

Patients

One hundred and five patients were recruited prospectively for 1 year in a university hospital. This group was compared to a historical cohort of 87 patients resolved at the same center. Demographic and clinical variables were comparable between both the groups. A more significant proportion of lithiasis in the proximal ureter in the cohort using fluoroscopy (23.5% vs. 13.1%, P < 0.001) and less use of preoperative double J stents in the radiation-free SR-URS (9.1% vs. 23.4%, P < 0.0091) were the main differences. In both the groups, every patient who had a preoperative stent had it installed in the context of urinary focus sepsis. The mean effective dose administered per patient in the conventional SR-URS was 0.5 mSV. Variables compared are shown in Table 1.

Table 1.

Demographic and clinical characteristics of patients

Characteristics	FF SR-URS (n=105)	FG SR-URS (n=87)	P
Median age (years) (range)	50 (42-60)	49 (40-61)	0.79
Sex, n (%)
Male	70 (67)	52 (60)	0.32‡
Female	35 (33)	35 (40)
BMI (kg/m2)	27.3 (25.8-29.9)	26.4 (23.4-29.0)	0.053†
Ureter localization, n (%)
Distal	78 (74)	56 (64)	0.069$
Mid	17 (16)	10 (12)	0.172$
Proximal	10 (10)	21 (24)	<0.003*,$
Dimension (mm)
Diameter	7 (5-8)	7 (6-9)	0.07†
Area	32 (26.6-48.8)	42 (26.5-66.5)	0.07†
Laterality, n (%)
Right	45 (43)	45 (52)	0.37‡
Left	59 (56)	42 (48)
Bilateral	1 (1)	0
Previous pigtail, n (%)	12 (9)	19 (23)	0.003‡,*
Hydronephrosis, n (%)
No	13 (12)	4 (7)	0.69‡
Minimum	47 (45)	40 (46)
Moderate	39 (37)	33 (38)
Severe	6 (6)	8 (9)
Operating time (min)	37 (29.75-57)	45 (35-55)	0.976†
Hounsfield units	766 (590-980)	902 (568-1065)	0.21†
Average fluoroscopy time (s)	-	46
Average effective dose (mSv)	0.6**	0.5

*P<0.05, **The average dose of the eight patients in whom fluoroscopy had to be used, ^†Mann-Whitney, ^‡χ², ^§Fisher’s exact test, ^$Two-sample test of proportions. FF: Fluoroscopy-free, SR-URS: Semirigid ureteroscopy, FG: Fluoroscopy-guided, BMI: Body mass index

Feasibility of fluoroscopy-free semirigid ureteroscopy

A successful FF SR-URS was achieved in 97 of 105 renal units (92.38%). In the remaining 8 cases, fluoroscopy was required to complete the procedure successfully: three safety guidewire installations, one laborious ascent of the ureteroscope to the lithiasis, and four postoperative double J stent installations. No statistically significant differences (of the calculus or patient) were found when comparing radiation-free SR-URS and conventional SR-URS [Table 2].

Table 2.

Feasibility of fluoroscopy-free semirigid-ureteroscopy and causes of failure

Characteristics	Successful without radiation (n=97)	Successful with radiation (n=8)	P
Number of SR-URS, n (%)	97 (92.38)	8 (7.62)
Age (years)	51 (42-58)	55 (50-61)	0.35†
BMI (kg/m2)	27.3 (25.7-29.9)	27.7 (25-29.5)	0.79†
Ureter localization, n (%)
Distal	73 (76)	5 (63)	0.19‡
Mid	14 (15)	3 (37)
Proximal	9 (9)	0
Dimension
Diameter (mm)	7 (5-8)	5 (4.8-6.5)	0.07†
Area (mm2)	35 (23-49)	25 (14.3-30.5)	0.03*,†
Laterality, n (%)
Right	41 (42)	4 (50)	0.69‡
Left	55 (57)	4 (50)
Bilateral	1 (1)	0
Previous pigtail, n (%)	10 (10)	2 (25)	0.22§
Hydronephrosis, n (%)
No	11 (12)	2 (25)	0.92‡
Minimum	44 (45)	3 (37.5)
Moderate	36 (37)	3 (37.5)
Severe	6 (6)	0
Hounsfield units (average or median)	766 (572-980)	757 (600-955)	0.76†
Cause of failure of radiation-free SR-URS		n=8
Unsuccessful ascent of the hydrophilic guide wire		3
Unsuccessful ascent of the ureteroscope		1
Pigtail positioning		4

*P<0.05, ^‡χ², ^§Fisher’s exact test. SR-URS: Semirigid ureteroscopy, BMI: Body mass index

Efficacy and complications

The efficacy of FF SR-URS measured as the stone-free rate was 92.45%. Our historical cohort’s stone-free rate was 94.25%, with no statistical difference between both the groups. Operative time was a bit shorter in FF SR-URS (37 min vs. 45 min). Postoperative pain measured using the Visual Analog Scale (VAS) 8 h after surgery was 59 (56%) patients without pain, 25 (24%) with mild pain (VAS 1–4), 9 (9%) with moderate pain (VAS 5–7), and 12 (11%) with severe pain (VAS 8–10).

Only three complications developed. Transient hematuria and extraluminal guidewire were classified according to the Clavien–Dindo classification as I, and renal colic due to a residual fragment classified as Grade II. There were no complications categorized as III or above [Table 3].

Table 3.

Efficacy and complications of fluoroscopy-free versus fluoroscopy-guided semirigid ureteroscopy

	FF SR-URS (n=105)	FG SR-URS (n=87)	P
Stone free, n (%)	98 (92.4)	82 (94.25)	0.079‡
Complication, n (%)
Yes	3 (2.9)	5 (5.7)	0.15‡
No	102 (97.4)	82 (94.3)
Type of complication (Clavien-Dindo)
Renal colic due to ureteral inflammation (II)	0	1
Renal colic due to residual lithiasis (II)	1	0
Contrast extravasation (I)	0	2
Hematuria (I)	1	1
Extraluminal guide wire (I)	1	0
Acute urinary obstruction (II)	0	1
Postoperative pain VAS, n (%)
No	59 (56)	52 (60)	0.57‡
Yes	46 (44)	35 (40)
Mild (1-4)	25 (24)	15 (17)
Moderate (5-7)	9 (9)	11 (13)
Severe (8-10)	12 (11)	9 (10)
Postoperative pigtail, n (%)
Tubeless	5 (5)	0	0.09‡
Ureteral catheter	43 (41)	28 (32)
Pigtail	57 (54)	59 (68)

*P<0.05, ^‡χ², ^§. FF: Fluoroscopy-free, SR-URS: Semirigid ureteroscopy, FG: Fluoroscopy-guided, VAS: Visual analog scale

DISCUSSION

Urolithiasis has a prevalence of 2%–3% in the general population, affects young people, and has a high recurrence rate of approximately 20%–40% at 5 years.[18] Diagnosis, treatment, and follow-up of this disease require radiological techniques that administer significant amounts of radiation to patients. Many of them are exposed to doses that are well beyond the upper limits recommended by international commissions.[19] Hence, reducing radiation exposure to both patients and health personnel is of utmost importance. Fluoroscopy during URS is a central part of radiation exposure in endourology that can be reduced to limit its deleterious effects.

Our study demonstrates that it is feasible to perform FF SR-URS. About 92.38% of the procedures were completed successfully without the use of X-rays. Efficacy, measured as the stone-free rate, and complication rate were similar to those of our historical cohort with FG SR-URS. The extraluminal guide complication was discovered by direct vision during the ureteroscope ascent. We believe that this could probably not have been avoided with the use of fluoroscopy since, in our usual practice, we use fluoroscopy only to confirm that the guide is in the renal pelvis and not during the guide’s ascent. The Clinical Research Office of the Endourological Society (CROES) study included approximately 8600 SR-URS reported a stone-free rate of 86% and a complication rate of 3.5%, similar to those observed in our study and previous reports.[20,21] Previous research explains the URS SR technique without fluoroscopy. In the same line as Olgin and colls, we have incorporated estimations of the appropriate length of the guidewire that should be outside the patient, according to sex, to give an objective reference of possible failure.[22] However, tactile cues were the most important aspect, according to our experience. The guide or the double J stent should be ascended/descended smoothly through the ureter with no difficulties. If noting any resistance, the procedure should be switched to FG mode.

Several groups have tried to diminish radiation exposure to both patients and health personnel during SR-URS. One of the strategies evaluated by Kokorowski et al. and cols was to study if there were differences in emitted radiation if the surgeon instead of an assistant managed the pedal triggering fluoroscopy. Their results showed that there were no statistical differences between both the groups,[13] concluding that this is not a relevant strategy to diminish ionizing radiation. Smith et al. compared pulsed versus continuous fluoroscopy, demonstrating that the first reduced fluoroscopic time and effective dose administered to the patient by 63%. There were no differences in the procedure outcome.[14] Finally, Danilovic et al. demonstrated that it is feasible to reduce standard fluoroscopic dose to a fourth without altering stone-free or complication rates.[23]

FF SR-URS is another strategy that seeks to minimize exposure to ionizing radiation. Olgin and cols have reported the feasibility and safety of URS for both ureteral and renal stones without the use of X-rays.[22] They retrospectively recruited 50 patients in which a similar SR-URS technique was employed, measuring the length of guidewires and catheters installed in terms of standard anatomic proportions. Similar to our findings, they did not report complications associated with the incorrect installation of a guidewire or double J stent postoperatively. Their global complication rate was 4%.[20] However, they did not report the feasibility or success rate of FF SR-URS as it is a retrospective study. In another study, Mandhani et al. presented a prospective cohort of 110 patients evaluating the feasibility of FF SR-URS.[24,25] They reported a success rate of 94%, similar to that of our series. However, their technique does not consider the use of safety guidewires nor standard anatomic reference measures. Only patients with distal ureteral lithiasis were included in their study.

Among other strategies to reduce X-ray exposure during SR-URS, the use of ultrasonography (US) instead of fluoroscopy has been reported to confirm the correct placement of guidewires and double J stents. Morrison and cols. Published experience of 12 patients in which US was employed to confirm correct guidewire positioning and then proceeded with SR-URS. Our FF SR-URS protocol does not include the support of any kind of imaging technique. Despite this difference, our stone-free and complication rates were similar to theirs.

Regarding ionizing radiation usage in our historical cohort with FG SR-URS, results are similar to those published by Lipkin and cols. Our cohort had a mean fluoroscopic time of 46 s and an effective dose of 0.5 mSv. Lipkin validated the doses of radiation delivered in a URS phantom model and demonstrated an average dose of 1.13 mSv (0.31–7.17 mSv) and 46 s of fluoroscopy.[26]

A limitation to our study is the risk of bias by comparing a prospective cohort of FF SR-URS and a retrospective historical cohort of FG SR-URS. Even if this historical cohort is from our same center and completed by identical surgical staff, the ideal would have been to randomize both the groups prospectively. Likewise, the design of this study does not allow to identify predicting factors of FF SR-URS. Further studies are required to address this issue.

CONCLUSIONS

Our FF SR-URS protocol provides a feasible, efficacious, and safe technique to treat the vast majority of ureteral stones, for urologists with good practice of the traditional SR URS technique, at the same time reducing ionizing radiation exposure of both patients and health personnel.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.