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Keywords:

  • shockwave lithotripsy;
  • ureteric stone;
  • distal ureter

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References

What's known on the subject? and What does the study add?

  • Shockwave lithotripsy (SWL) can be used to treat stones at any position within the ureter, as long as the stone is radio-opaque and there is a path for the shockwave to reach the stone. However the results of SWL to distal ureteric calculi, with the patient in a prone position, were inferior to those of treating stones within the upper ureter.
  • The transguteal approach allows the lithotripsy shockwave to reach the lower ureter via the greater selatle foramen. This study shows that this approach for SWL to distal ureteric calculi is more effective than the prone approach.

Objective

  • To compare the outcomes of extracorporeal shockwave lithotripsy (ESWL) for distal ureteric stones treated using the prone and transgluteal (supine) approaches in a tertiary referral stone unit using a fourth generation lithotriptor.

Patients and Methods

  • We selected consecutive patients undergoing ESWL to distal ureteric stones over 1 year, during which we changed our treatment protocol from a prone to transgluteal (supine) approach.
  • Patients were treated using the Sonolith Vision Lithotriptor (Technomed Medical Systems, Vaulx-en-Velin, France).
  • Outcome was assessed using plain abdominal film of kidney, ureter and bladder (KUB) X-ray taken at 2 weeks then monthly as required.
  • Treatment success was defined as complete clearance of stone fragments and treatment failure was defined as persistence of stone fragments beyond 3 months or the need for ureteroscopy.

Results

  • A total of 38 patients were treated in the prone position and 72 patients using a transgluteal approach.
  • Patient and stone characteristics were identical in both groups. The mean (range) stone size was 7.8 (4–16) mm.
  • The proportions of patients who were stone-free after one treatment session within the prone and transgluteal treatment groups were 40 and 78%, respectively (<0.001).
  • The overall success rates for treatment within the prone and transgluteal groups were 63 and 92%, respectively (<0.001).

Conclusions

  • Transgluteal ESWL to stones within the distal ureter leads to significantly higher stone-free rates than treatment using the prone approach.
  • The majority of patients are rendered stone-free after one session of treatment and the overall success rates are similar to those of ureteroscopic management.

Abbreviations
KUB

plain abdominal film of kidney, ureter and bladder

SFR

stone-free rate

SSD

skin-to-stone distance

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References

The introduction of ESWL in the early 1980s revolutionized the management of urinary stone disease. Today, ∼80% of urinary tract stones are managed with ESWL. Initially a treatment for renal and upper ureteric stones, it soon became clear that ESWL could also be used to treat stones within the mid and distal ureter [1]. Renal and upper ureteric stones were treated with the patient in the supine position, with the shockwave treatment head in contact with the posterior or lateral aspect of the patient's abdomen. As the bony pelvis prevented transmission of the shockwave to the mid or distal ureter, distal ureteric stones were treated with the patient prone and the shockwave source in contact with the patient's anterior abdomen. This was shown to be a safe and effective method of treating stones within the distal ureter [2, 3].

Audit within our institution has shown that ESWL outcomes with the Sonolith Vision Lithotriptor (Technomed Medical Systems, Vaulx-en-Velin, France) are similar to those of the Dornier HM-3 (Dornier Medtech Systems) [4] with the exception of distal ureteric stones. This observation prompted a review of our treatment protocols for patients with distal ureteric stones.

The use of a transgluteal approach to the distal ureter has been described previously with the use of the Dornier HM-3 [4]. We initially adopted this approach in those patients where treatment in the prone position was not possible. The patient lies supine, and treatment is delivered via the gluteus maximus muscle. The shockwave travels via the greater sciatic foramen to the distal ureter, unimpeded by bony structures.

The objective of the present study was to compare the outcomes of ESWL for distal ureteric stones treated by the prone and transgluteal approaches in a tertiary referral stone unit using a fourth generation lithotriptor.

Patients and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References

We conducted a retrospective review of a sample of 110 consecutive patients undergoing lithotripsy for distal (below the level of the sacroiliac joint) ureteric stones over a period of 1 year, during which we changed our protocol for treating distal ureteric stones from the prone to transgluteal (supine) approach. Patients with radio-opaque and previously untreated solitary ureteric stones were selected from our prospectively maintained database. Those with nephrostomy or ureteric stents in situ were excluded from the study. Treatments were either entirely prone or entirely supine, with no patient included in the study undergoing a change of position during the course of treatment.

Patients were treated on the Sonolith Vision Lithotriptor in either the prone or transgluteal treatment position. The treatment protocols were identical for both approaches and have been described previously [5]. All treatments were undertaken using a shockwave frequency of 2 Hz by the same team of radiographers under the supervision of the same urologist.

Figure 1 shows a plain abdominal film of kidney, ureter and bladder (KUB) X-ray of a patient with a 7-mm stone within the right distal ureter, over the lower edge of the sacrum. Figure 2 shows a three-dimensional reconstruction of the same patient and shows that there is a path for shockwaves to travel from the gluteal region through the greater sciatic foramen to the stone within the lower ureter. The treatment table of the Sonolith Vision Lithotriptor has a space for the treatment therapy head which is placed against the skin of the patient. The treatment head is fixed at an angle of 40° to the vertical and, for transgluteal treatment, the patient is positioned supine with the therapy head against the patient's buttock (Fig. 3). The patient's head and legs are usually raised by pillows for comfort.

figure

Figure 1. Plain KUB X-ray showing right lower ureteric stone.

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figure

Figure 2. Three-dimensional reconstruction from CT imaging of the patient shown in Fig. 1. This shows the path of the shockwave to the distal ureteric stone via the gluteal region and greater sciatic foramen.

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figure

Figure 3. Patient position for transgluteal ESWL treatment of the distal ureter. The treatment head is positioned against the buttock.

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Treatment outcome was assessed by plain KUB X-ray at 2 weeks after treatment and then at monthly intervals after treatment if required. A second session of lithotripsy was used if no fragmentation was evident after initial treatment as assessed at the 2-week post-treatment KUB. In this situation, the second session of treatment took place on an urgent outpatient basis. α-blockers were not used after treatment. Treatment success was defined as complete clearance of stone fragments. Treatment failure was defined as persistence of stone fragments beyond 3 months or the need for ureteroscopy. Statistical analysis was carried out using the Students t-test and Fisher's Exact Test and a P valu <0.05 was considered to indicate statistical significance.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References

A total of 110 patients satisfied the inclusion criteria for the study, of whom 38 patients were treated in the prone position and 72 in the supine position. There was no significant difference in patient and stone characteristics between the two groups (Table 1). The mean (range) stone sizes within the prone treatment and transgluteal treatment groups were 7.9 (4–16) mm and 7.6 (4–16) mm, respectively (P = 0.5).

Table 1. Patient, stone and treatment characteristics and results of treatment.
 Treatment groupP
ProneTransgluteal
No. of patients3872 
Mean (sem) patient age, years48.3 (2.2)51.3 (1.8)0.3
Patient gender male, n (%)31 (82)58 (81)1.0
Mean (sem) stone size, mm7.9 (0.4)7.6 (0.3)0.5
Mean (sem) no. of shocks used 1st session3997.9 (225)4053.2 (154.7)0.8
Mean (sem) power used 1st session, % of maximum71.4 (1.9)70.7 (1.6)0.8
Stone-free after 1st treatment session, n (%)15 (40)56 (78)<0.001
Stone-free after 2nd treatment session, n (%)24 (63)66 (92)<0.001

ESWL treatment characteristics and the results of treatment are shown in Table 1. The number of shocks and the power used for ESWL treatments within both groups were identical.

The proportions of patients who were stone-free after one treatment session within the prone and transgluteal treatment groups were 40 and 78%, respectively (<0.001). The proportions of patients proceeding to ureteroscopy after failing to clear the stone after the second session of ESWL within the prone and transgluteal treatment groups were 37 and 8%, respectively. The overall success rates for treatment within the prone and transgluteal treatment groups were therefore 63 and 92%, respectively (<0.001).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References

The standard management options available for the treatment of ureteric stones unsuitable for conservative management are ESWL and ureteroscopy [6]. The outcomes from the treatment of proximal ureteric stones on the Sonolith Vision Lithotriptor within our institution are similar to those of the Dornier HM-3 [7]; however, the results of treating distal (distal to the sacroiliac joint) ureteric stones with ESWL were disappointing, especially in the context of the high success rates seen with ureteroscopic management. This prompted a review of our treatment protocols.

We had previously undertaken ESWL to distal ureteric stones with the patient in the prone position. It was believed that supine treatment was not possible because of the presence of the bones of the pelvis preventing passage of the shockwave to the distal ureter. In prone treatment, the lithotriptor treatment head is in contact with the patient's anterior abdomen and the shockwave travels to its target across the abdominal wall, bowel, and/or the bladder depending upon the stone position. The skin-to-stone distance (SSD) is often significantly greater in this group and the shockwave may be attenuated by the presence of bowel gas as it travels to the focal point.

The transgluteal position is usually ideal for directing the shockwave through the posterior pelvis and avoiding bony structures. Accurate localization of the stone can be achieved by cranio-caudal movement or rotation of the patient in either direction. One obstacle to adequate treatment sometimes encountered is pain resulting from the proximity of the shockwave to the sciatic nerve at the focal area. The nerve cannot be seen on imaging and, in this situation, small adjustments in patient position and therefore the treatment angle (within the limitations of the bony pelvic anatomy) can often alleviate this problem. As such, successful treatment of stones in this position is very much operator-dependent. Some lithotriptors (such as the machine currently in use in our institution) have a mobile therapy head which facilitates changes in position without the need to move the patient and allows accurate localization of the stone. Our experience is that the supine position is better tolerated by patients, especially by those who are elderly or obese, or those with poor mobility.

Early assessment of the outcomes of the transgluteal approach within our institution were so encouraging that we began a prospective audit of treating all distal ureteric stones in this way. Whilst we acknowledge that this is not a prospective, randomized trial, our cohort study compares consecutive patients taken from our prospectively maintained database. There was no significant difference between patient and stone characteristics within the groups compared. The majority of patients within the study were male (82% of prone treatments and 81% of transgluteal treatments); we do not treat women of child-bearing age with lithotripsy to stones in the pelvic ureter as the effect of shockwave energy on the ovaries is unknown.

Patients undergoing treatment to distal ureteric stones in the prone position in our study had stone-free rates (SFRs) of only 63%. SFRs after ureteroscopic management of distal ureteric stones can be expected to be at least 95% [8]. The number of shocks and amount of power administered during the ESWL treatments in the present study were identical for both the prone and transgluteal approaches (Table 1).

We believe there are a number of reasons why the outcomes are inferior after prone treatments despite the administration of the same amount of energy. In the prone approach, the shockwave is more likely to pass though the bowel (depending upon the stone position). Bowel gas has the effect of attenuating the shockwave, which therefore delivers less energy at its second focus. In the transgluteal approach the shockwave travels through muscle and the greater sciatic foramen to the distal ureter, unimpeded by bowel gas. Secondly, the SSD for the distal ureter is usually greater from the anterior aspect than the posterior. This is increasingly the case as we are managing greater numbers of obese patients [9]. The stone is therefore more likely to be towards the limit of the focal depth of the lithotriptor in the prone position: SSD has been shown to be an independent predictor of outcome from ESWL [10]. Furthermore, visualizing the distal ureteric stone by fluoroscopy can be more difficult in the prone position for the same reasons, which may further compromise the efficacy of treatment.

It is also interesting to consider the reasons for failure of the transgluteal approach in the present series. Six of the patients treated by transgluteal ESWL proceeded to ureteroscopy. Two of these patients were noted to have very hard stones at ureterorenoscopy and laser fragmentation. One patient's stone fragmented but did not clear after treatment. This was a 13-mm stone which was found to be associated with significant ureteric oedema at ureteroscopy. The reasons for the remaining three patients to fail to respond to ESWL are not clear, but are likely to be a combination of factors such as the SSD, pain during treatment limiting efficacy, and the characteristics of the stone. Unfortunately, many of the patients treated in this series did not undergo CT KUB, as they were treated when IVU was still in routine use for imaging stones in our institution, so SSD data are not available. Similiarly, the HU values for the stones treated are not available, so whether HU had any bearing on the responses to treatment is also unclear.

The successful application of transgluteal ESWL for distal ureteric stones has also recently been reported by a number of other groups worldwide. Lu et al. [11] and Sun et al. [12] have reported use of the technique in the treatment of distal ureteric stones in both children and adults. They did not, however, compare outcomes with those of the prone approach. Istanbulluoglu et al. [13] did, however, retrospectively compare the supine and prone approaches and reported superiority of the supine approach as in the present series. The present study confirms that the outcome of ESWL via the transguteal approach to the distal ureter was far superior to the prone approach and the SFR after ESWL to distal ureteric stones in the transgluteal treatment position was similar to those of ureteroscopic management.

In conclusion, transgluteal ESWL to stones within the distal ureter with the patient in the supine position leads to a significantly higher SFR than for those treated in the prone position. The majority of patients are rendered stone-free after one session of treatment and the overall success rates are similar to those of ureteroscopic management. This technique is now in routine use in our institution.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Conflict of Interest
  8. References