Introduction

In the modern era of management of renal stones, the preferred first-line treatment of stones less than 1 cm is shockwave lithotripsy (SWL) whereas treatment for stones more than 2 cm is most commonly percutaneous nephrolithotomy (PNL). There is most controversy in the management of kidney stones between 1 and 2 cm. International guidelines agree that SWL, ureteroscopy (URS) and PNL are all acceptable treatment options for these stones [1].

Recent literature favours PNL for 1- to 2-cm lower pole stones [2]. The recent miniaturisation of PNL (e.g., mini-perc, ultra-mini-PNL, and micro-perc) has made PNL an even more attractive option because of reduced morbidities and high stone-free rate [3–5]. Flexible URS is also promoted by others as a promising technique for these calculi. Given the choice of endourological options available, urologists need to balance the outcomes of these technologies against the success of low-risk, non-invasive techniques such as lithotripsy to provide patients with accurate information for consent.

In this study, we have reviewed the efficacy of SWL in treating larger kidney stones (10–20 mm) with regard to stone location and size.

Patients and methods

Since 2013 all patients undergoing SWL in our unit were entered into a prospective database. Patient demographics including gender, age and body mass index (BMI) were recorded. Treatment details such as stone size, location, number of shock waves, energy delivered and treatment success were documented.

From January 2013 to October 2014, all patients with a single, radio-opaque renal stone measuring between 10 and 20 mm in maximum diameter on non-contrast enhanced computer tomography (NCCT) were included. 130 consecutive patients were eligible and evaluated. The SWL was carried out as outpatient procedures. All lithotripsy treatments were performed on an on-site Modulith SLX-F2 lithotripter and by experienced dedicated radiographers. Fluoroscopy was used for stone targeting. All patients received the same pre-procedure analgesia, antiemetic and prophylactic antibiotics (pethidine 100 mg intramuscularly, diclofenac 100 mg per rectum, prochlorperazine 3 mg buccally, nitrofurantoin 100 mg orally). Our patients were not routinely stented before lithotripsy treatment except under the circumstances that a ureteric stent was inserted due to uncontrolled pain. We aim to deliver 4000 shock waves for each treatment session and this was reduced if the patient could not tolerate the pain or the stone was adequately fragmented. The patients were reviewed by urologists after every two treatments to decide if further lithotripsy treatment was warranted. No routine medical expulsive therapy was given post-treatment.

Patients attended for a radiological follow-up by plain X-ray 2 weeks after completion of all lithotripsy sessions. Treatment success was defined as complete stone free or clinical insignificant residual fragments (CIRF) <4 mm. Complication rates including hospital attendance with renal colic, haematuria, urinary infection or steinstrasse (log-jam) were recorded. Need for any adjunctive surgical procedures was documented. For those patients that failed SWL, the long-term management plan was recorded.

Results

A total of 119 patients (92 %) completed lithotripsy treatment and radiological follow-up. Eleven patients were excluded due to incomplete follow-up data. Patient demographics are summarised in Table 1.

Table 1 Patient demographics
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Overall treatment success was 66.4 % (combined complete stone clearance and CIRFs). The treatment success was similar by stone location (Table 2). Those with stone size <15 mm had a higher success rate (70.4 %) compared to size 15–20 mm (53.1 %) (Fig. 1). Regarding patients who failed SWL treatment, the majority 50 % (n = 20) were managed expectantly, 42.5 % (n = 17) required URS, 7.5 % (n = 3) required PNL (Fig. 2).

Table 2 Treatment success by stone location
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Fig. 1
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Treatment success according to stone size

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Fig. 2
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Patient outcome if SWL has failed

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The overall complication rate including hospital admission for renal colic, urinary tract infection, haematuria, steinstrasse or auxiliary measures is summarised in Table 3.

Table 3 Complication rates
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Discussions

Epidemiological data suggest a global trend away from SWL to flexible URS and PNL [6]. Recent studies continue to debate the relative merits and outcomes of SWL, URS and PNL [7, 8]. Randomised controlled trials that examine both stone-free status and quality of life are required to address these issues. However, SWL offers a non-invasive, low-risk option that can be delivered without anaesthesia.

With an ageing population, more urological patients present with medical co-morbidities posing increased surgical and anaesthetic risks. With the available options, it is important to balance the risk against the success rate of each procedure based on patient characteristics and surgeon expertise. In this study, half of the patients that failed treatment were managed conservatively mostly because of other significant morbidities that made surgery high risk.

In our series, the overall stone-free rate was 66.4 % for renal stones (10–20 mm) at all locations. The efficacy was comparable to larger series of smaller kidney stones [9–11]. Our outcomes for larger lower pole stones (10–20 mm) were favourable in comparison to previous studies [12] but comparable to more recent studies [13].

In our centre, NCCT is used for pre-treatment stone diagnosis and patients return for follow-up with plain X-ray 2 weeks post-treatment. Repeating NCCT as a routine follow-up carries excessive radiation for the patients, and therefore, is not performed. Admittedly, plain X-ray has a much less sensitivity than NCCT to detect residual fragments, which may lead to higher observed stone-free rate. In our unit, we assessed our patients relatively early post-SWL to detect early treatment-related complications. More spontaneous stone fragment passage and a higher treatment success will be expected, if we could review the patients at 3-month interval.

Need for retreatment is one of the disadvantages of SWL compared with retrograde intra-renal surgery, which allows a better chance to achieve stone free in a single session [14]. In our series, the average number of treatments was between 2.14 and 2.82 depending on stone size. The clinician needs to inform the patients of the possibility of multiple treatments in particular for larger renal stones.

In line with other studies [15], our study demonstrated low complication rates even with multiple SWL treatments. In this study, most complications were managed conservatively. Renal colic episodes were occasionally treated with additional SWL. Only 3 (2.5 %) patients required auxiliary procedures. These patients underwent emergency stent insertion or ureteroscopy due to inadequate pain control. This compares favourably with other series [15, 16]. The rate of steinstrasse was 2.5 %, which is consistent with the published literature for all stone sizes [17]. Despite the large stone size, we did not see an increase in post-SWL complications. The rate of haematuria and urinary tract infection (<1 %) was also comparable with larger series [18]. There were no incidences of renal haematoma or sepsis in this study.

This study supports other large international series that equivalent stone clearance rates are possible with SWL irrespective of stone site in the kidney. Further studies are needed to establish if other factors such as stone to skin distance have an impact on the SWL treatment success rate.

In conclusion, our analysis suggests that SWL has an efficacy for treating moderate-sized renal stones that is equivalent to success rates for smaller stones in other series. As a low-risk and non-invasive procedure SWL should remain a first-line treatment option for 10- to 20-mm renal stones particularly in patients with other co-morbidities.