Success of Extracorporeal Shockwave Lithotripsy for Distal Ureteric Stones in Patients With and Without Hydronephrosis

ABSTRACT

INTRODUCTION: The purpose of the present study was to verify whether ureteral obstruction due to solitary distal ureteric stones affects the outcome of extracorporeal shock wave lithotripsy (ESWL).

METHODS: The prospective study included 120 patients with solitary distal ureteral stones that were 6-15 mm in length and located below the lower border of the sacroiliac joint. Patients were assigned to one of 4 groups according to the degree of dilatation of the urinary system. Group 1 (n = 51; 42.5%) had no dilatation; group 2 (n = 41; 34.2%) had mild dilatation; group 3 (n = 20; 16.6%) had moderate dilatation; group 4 (n = 8; 6.7%) had severe dilatation. All patients underwent ESWL using the Siemens Lithostar Plus lithotripter (Siemens Corp; New York, NY, USA). Outcome measures were stone-free rates, number of treatment sessions, stone clearance time, and number and power of the shock waves used. Groups were compared using t and chi-square tests.

RESULTS: Three months after the last ESWL session, 95 patients (79.2%) were stone free, 6 patients (5%) had insignificant residual stones, and 19 patients (15.8%) had treatment failure. There was no significant difference in the ESWL outcomes across groups (P = .41). Patients with hydronephrosis required significantly more treatments than patients without obstruction (P < .002). The mean number of days needed to clear the stones progressively increased as hydronephrosis severity increased (P = .007). The groups with hydronephrosis required a significantly larger mean number of shock waves (P < .001). There was no significant group difference in the mean shock wave power used (P = .39).

CONCLUSIONS: The presence or degree of hydronephrosis did not significantly affect the overall success of ESWL in treating single distal ureteral stones measuring ≤ 15 mm. However, the presence of hydronephrosis significantly increased the retreatment rate and number of shock waves needed to clear the stone. Hydronephrosis also increased the interval to stone clearance.

Hashem Hafez, Mohamed Hassan Ali, Tarek Salem

Department of Urology, Faculty of Medicine, Suez canal University, Ismailia, Egypt

Submitted July 22, 2010 - Accepted for Publication August 23, 2010

KEYWORDS: Stones; Lower ureter; Extracorporeal shock wave lithotripsy.

CORRESPONDENCE: Dr. Tarek Salem, Department of Urology, Suez Canal University, Faculty of Medicine, Ismailia 31911, Egypt ().

CITATION: Urotoday Int J. 2010 Oct;3(5). doi:10.3834/uij.1944-5784.2010.10.05

ABBREVIATIONS AND ACRONYMS: ESWL, extracorporeal shock wave lithotripsy

INTRODUCTION

Since its initial application in 1980 [1], the use of extracorporeal shock wave lithotripsy (ESWL) has rapidly extended from stones in the kidney to stones in almost the entire urinary tract. It is the least invasive and most widely accepted form of treatment for ureteric stones [2,3,4,5,6]. In situ ESWL has been shown to be effective for ureteric stones at all levels [7,8].

Controversy arises about preferred treatment choice for ureteric stones with obstruction. The in situ ESWL procedure appears to be the preferred treatment option [9]. However, success rates depend on factors such as stone site, size, chemical composition, impaction, degree of obstruction, and overall kidney function [10]. Some studies have revealed that patients with obstruction had lower success rates than those without obstruction [11]; other studies have shown that there was no comparative difference [12]. It has been reported that ESWL with the patient in the prone position is a safe and effective form of treatment for calculi in the distal ureter [13]. The purpose of the present study was to verify whether ureteral obstruction due to solitary distal ureteric stones affects the outcome of ESWL.

METHODS

The study protocol was approved by the hospital ethics committee. All participants provided informed consent. They were provided with a description of alternative available treatments and management procedures for failed treatment. The prospective data collection was completed over a 2-year period, 2007-2009.

Participants

The participants were 120 patients with solitary distal ureteral stones measuring 6-15 mm in length and located below the lower border of the sacroiliac joint. The criteria for exclusion were ureteral strictures, single or nonfunctioning kidney, previous stone manipulation, multiple stones, radiolucent stones, congenital renal abnormality, pregnancy, and coagulopathy.

All patients received a complete medical history, clinical examination, plain abdominal x-ray, and ultrasonography of the abdomen and pelvis. Excretory urography was only completed for patients with serum creatinine < 1.8 mg/dL. Laboratory investigations included urinalysis, urinary culture and sensitivity, serum creatinine, and coagulation profile. Urine culture was positive in 7 patients (5.8%); these patients were treated with the proper antibiotics before beginning the study protocol.

The degree of hydronephrosis attributable to the stone was evaluated by ultrasonography, which was performed by a senior radiologist who also assessed all intravenous urograms. The participants were divided into one of 4 groups according to the degree of dilatation of the pelvicalyceal system: group 1 (n = 51; 42.5%) had no dilatation of the urinary system; group 2 (n = 41; 34.2%) had mild dilatation; group 3 (n = 20; 16.6%) had moderate dilatation; group 4 (n = 8; 6.7%) had severe dilatation.

Overall, the participants had a mean age of 43.2 years (SD, 11.1; range, 20-72 years). There were 81 males (67.5%) and 39 females (32.5%). The stones were on the right side for 57 patients (47.5%) and the left side for 63 patients (52.5%). The mean stone length was 7.2 mm (SD, 2.6; range, 6-15 mm). The mean stone width was 5.2 mm (SD, 1.1; range 4-9 mm). Table 1 contains the age, sex, stone side, stone length, and stone width characteristics for each participant group. There were no significant group differences for these characteristics (P > .05).

Procedures

All patients underwent ESWL within 3 days of diagnosis. The Siemens Lithostar Plus lithotripter (Siemens Corp; New York, NY, USA) was used. Patients were treated in the prone position. All patients received meperidine hydrochloride (1 mg/kg) as an analgesic, which was started while the patient was on the table. A total of 3000 shocks were delivered at each session, until there was complete fragmentation of the stone. The power used was 14 kV, which was then increased gradually to a maximum of 24 kV.

Repeat Treatment

Follow-up evaluations started 1 week after the first session. Plain abdominal x-ray was used to assess fragmentation. Repeat treatment was done immediately if inadequate fragmentation of the stone was observed. The length of time between the repeated sessions was the same for all groups. Follow-up was made every week by plain x-ray and every month by ultrasound. The final evaluation was done 3 months after the last ESWL session. Plain abdominal x-ray and renal ultrasonography were used to assess the stone-free status and hydronephrosis response.

Data Analysis

ESWL success was defined as complete clearance of the stone with no residual fragments; ESWL failure was defined as no breakage of the stone after 2 sessions. Other outcome measures were the number of treatment sessions, stone clearance time, and number and power of the shock waves used.

Group mean differences in the continuous variables were determined using the t test. The chi-square test was used for categorical variables. A probability value < .05 was considered statistically significant. A power analysis was not performed. Therefore, the possibility of a type II error exists with this sample size.

RESULTS

ESWL Outcomes

Stone-free rates and stone clearance times by group. Table 2 contains the number of patients with stone-free success or failure for each patient group and the mean number of days needed to clear the stones. There was no significant group difference in the ESWL outcomes across groups (P = .41). There was a significant difference in clearance time (P = .007); the mean number of days needed to clear the stones progressively increased as hydronephrosis severity increased.

Number of treatment sessions. Complete stone fragmentation was achieved after 1 session in 55 patients (57.9%), after 2 sessions in 19 patients (20%), after 3 sessions in 12 patients (12.6%), and after more than 3 sessions in 9 patients (9.5%). Table 2 contains the mean number of ESWL sessions for each group. The number of patients needing multiple treatments in each group was 16 patients (31.4%) in group 1 (no dilatation), 27 patients (65.8%) in group 2 (mild dilatation), 14 patients (70%) in group 3 (moderate dilatation), and 6 patients (75%) in group 4 (severe dilatation). There was a statistically significant difference between the 4 groups with respect to these frequencies (P < .002). The mean number of sessions in group 1 (no dilatation) was 1.6. This mean was compared with the overall mean number of sessions of 2.2 for groups 2, 3, and 4 (with dilatation). The groups with hydronephrosis required significantly more sessions (P < .001). A larger number of patients in the groups with hydronephrosis required multiple treatments.

Number of shock waves and shock wave power. Table 2 contains the power and number of shock waves used for each patient group. The mean number of shock waves in group 1 was 4225. This mean was compared with the overall mean number of shock waves of 6325 for groups 2, 3, and 4. The groups with dilatation required a significantly larger number of shock waves (P < .001). The median power used was 16 kV (range, 14-24 kV). There was no significant difference in the mean power used for group 1 when compared with the overall mean power used for the other groups (P = .39).

Follow-up Treatment

Of the 25 patients with ESWL failure, 6 patients had residual stones that were < 4 mm; these stones were treated conservatively. The remaining 19 patients with stones that were not disintegrated were treated with ureteroscopy with 100% success.

DISCUSSION

Some investigators suggest that both the degree of obstruction and the physical properties of the stone (eg, site, size, chemical composition) affects the success of stone fragmentation [14]. This hypothesis has led some investigators to recommend insertion of double-J stents in patients with a significant degree of stone-induced obstruction, or surgical removal to prevent progressive kidney dysfunction or severe complications [15].

ESWL is an attractive line of treatment for obstructing ureteral stones because it is a noninvasive procedure that can be performed without anesthesia. However, previous studies using ESWL to treat obstructive stones show mixed results. Delakas and colleagues [14] found an increased failure rate of ESWL with more severe obstruction. Others found that middle and lower ureteral calculi and moderate to severe hydronephrosis were factors that worsened ESWL outcomes [11]. Conversely, Kirkali et al [16] found that no degree of hydronephrosis affected the success of the stone disintegration or passage with ESWL. The success rate for distal ureteric stones has been reported to range between 53% and 84% [17,18].

In the present study, the overall stone-free rate 3 months after the last treatment session was 79.2%. The stone-free rate was 86.3% in patients without hydronephrosis and 73.2% in patients with hydronephrosis; the difference was not statistically significant (P = .14). These results are in accordance with those of other investigators [16,19,20,21] who reported that neither the presence nor the degree of hydronephrosis had a significant effect on the success rates of ESWL.

el-Assmy et al [21] used ESWL to treat solitary distal ureteral stones ≤ 20 mm in length. They found that the presence of hydronephrosis significantly increased the retreatment rate and prolonged the interval to stone clearance. These results were confirmed by the present study, which also showed that the groups with hydronephrosis required significantly more sessions and a significantly larger mean number of shock waves.

Ureteral obstruction results in decreased renal function and rapid changes in peristaltic activity due to hypertrophy of the ureteral musculature after only 3 days of obstruction [22]. Ureteral obstruction results in decreased peristalsis and decreased pressure, affecting ureteral stone migration. In the present study, ESWL was started at a low power of 14 kV and increased gradually to 24 kV. The focus was started at the periphery and moved toward the center of the stone. This procedure has the advantages of improving fragmentation and creating very fine fragments that can pass freely without causing obstruction or steinstrasse. The nil incidence of steinstrasse in the present study supports this policy.

One possible limitation of the present study was the range in size of ureteral calculi. The size of the calculus is known to be a significant variable affecting the outcome of ESWL. Therefore, although there were no significant group differences in stone size, a more homogeneous group may have affected the potency of statistical analysis.

CONCLUSION

The results of the present study showed that in patients with single distal ureteral stones measuring ≤ 15 mm in length, the degree of hydronephrosis caused by the stone did not significantly affect the overall treatment success of ESWL. However, the presence of hydronephrosis significantly increased the interval to stone clearance, retreatment rate, and number of shock waves needed to clear the stone.

Conflict of Interest: none declared

REFERENCES

Chaussy C, Brendel W, Schmiedt E. Extracorporeally induced destruction of kidney stones by means of shock waves. Lancet. 1980;2(8207):1265-1268.

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