Ureteroscopy (URS) has become the number 1 therapeutic intervention for treating upper urinary tract stones in North America . The miniaturization of flexible endoscopes and advances in ancillary devices, such as baskets and ureteral access sheaths, along with the proven ability of the holmium laser to fragment all stone compositions, have led to a revolution in retrograde intrarenal surgery (RIRS). Perhaps nowhere is the adoption of RIRS more evident than in the treatment of patients with lower pole stones.
It was not too long ago when a surgeon considering endoscopic treatment of a lower pole stone would be surrounded with uncertainty regarding a number of technical aspects: successful access to the lower pole, concerns about breakage of the endoscope when working in the lower pole, or the inability to insert the laser fiber in a tight lower pole. However, new instrumentation and technology, such as high-quality small core laser fibers, changes in laser fiber tip design, and the advent of highly deflectable single-use ureteroscopes have decreased the unpredictability and increased the success of treatment. The lower pole stone can no longer be considered the Achilles heel of flexible URS, and it now exists as a viable challenger to percutaneous nephrolithotomy (PCNL) for stones between 1 and 2 cm in size.
The ball-tip fiber has been specially designed to facilitate RIRS of lower pole stones. The ability to pass the fiber through a flexed scope is advantageous as the traditional maneuver of straightening the scope to advance the fiber risks difficulty in regaining access in patients with acute infundibulopelvic angles. Passing a conventional flat-tip fiber into a flexed scope can damage the working channel resulting in repair of the scope at considerable expense. Compared with flat-tip fibers, the insertional force of ball-tip fibers in the deflected scope is significantly lower, which can be helpful in prolonging the life of reusable scopes . In a recent study evaluating fiber passage, ball-tip fibers were able to successfully pass through maximum deflection angles of up to 270° . This study also showed that small (200-μm) fibers that had their tip cut off (i.e. cleaved) had comparable passage abilities to ball-tip fibers, and thus can be a less costly alternative for lower pole stones. In conjunction with the tip profile, laser fiber quality is also an important factor. The critical deflection angles encountered in the lower pole can decrease total internal reflection resulting in photon leakage and scope damage. The use of single-use fibers may prevent laser failure related to the lower pole, and if using a reusable scope, is a parameter that can improve performance .
Single-use flexible digital scopes offer another means to safely and efficiently treat stones in the lower pole where scope damage is likely. Devices, such as the Lithovue (Boston Scientific, Marlborough, Massachusetts, USA) provide a wide field of view and excellent optical resolution, and offer a small loop diameter with preservation of deflection, which can help access stones in challenging lower pole systems . Leveillee and Kelly  using a single-use scope, reported on the successful treatment of a 1.4 cm lower pole stone located at a 180° angle to the infundibulum in a single session. Although the costs of single-use scopes are currently high and prohibitive for wholesale adoption in high-volume centers, one emerging indication for their use is in patients with lower pole stones.
In contrast to PCNL, which requires a high level of expertise to perform percutaneous puncture in conjunction with a hospital stay for the patient, flexible URS offers the patient lower morbidity in an ambulatory environment. A systematic review comparing PCNL with flexible URS found that although PCNL resulted in significantly higher stone-free rates (SFRs), it was associated with greater complications and longer hospital stay . Interestingly, when comparing flexible URS with minimally invasive PCNL, the SFR was higher after URS. More recently, two randomized controlled trials comparing PCNL with flexible URS for lower pole stones provide evidence of the high performance of URS. Bozzini et al. compared standard PCNL to flexible URS in 388 patients, whereas Kandemir and colleagues compared micro-PCNL to flexible URS in 60 patients. Both studies showed that URS was associated with shorter hospital stay, significantly lower fluoroscopy times, and comparable complication rates. Importantly, there were no differences in the 3-month SFRs; 87.3% for PCNL vs. 82.1% for URS , and 83.3% for micro-PCNL vs. 86.7% for URS .
So how do we guide our patients on what is the best surgical option? Surgical decision for a 1.5 cm lower pole stone has to take into account multiple factors including treatment success and morbidity, patient risk factors, surgeon expertise, equipment availability and cost, and patient preferences (Table 1). For 1–2 cm size lower pole stones, European Association of Urology guidelines recommend either PCNL or URS in patients with unfavorable factors for shockwave lithotripsy (SWL) . In contrast, the American Urological Association (AUA) guidelines recommend URS as first-line therapy for lower pole stones greater than 1 cm, whereas PCNL is recommended for stones greater than 2 cm . However, the AUA panel advises that clinicians should inform patients with lower pole stones greater than 1 cm that PCNL provides higher SFRs, but at the expense of greater morbidity.
Patients do not necessarily prioritize decision-making based on treatment success. Omar and co-workers performed a survey of patients provided a hypothetical treatment scenario of an 8 mm lower pole stone and found that although patients ultimately relied on the physician's recommendations, patients preferred SWL over URS or surveillance, despite being told that URS had the highest rate of success . This study demonstrates that patients rank risk and success differently based on past exposure to pain and familiarity with a procedure. Each patient has to balance the pros and cons of PCNL and URS and determine, which approach makes sense for them based on their unique experiences, social and occupational factors.
To conclude, there is no ‘must do’ or ‘must not’ choice between URS and PCNL for a 1.5 cm LP stone. Physicians and patients should incorporate shared decision-making to make personalized selections best for that individual patient. The reality is that our field has made tremendous advances in the performance of RIRS, and we suspect the trend for the retrograde treatment of kidney stones less than 2 cm is likely to continue. Sir Henry Morris , the pioneer of nephrolithotomy prophesized our current journey in 1880, when he remarked after his first nephrolithotomy: ‘this case demonstrated for the first time that a stone could be removed safely by cutting freely upon it through a thick layer of renal tissue. It thus became the starting point of both the development and the conservatism of renal surgery, which I am persuaded will become more and more conservative in the future’.
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Conflicts of interest
K.R.G. is a consultant for Boston Scientific and Lumenis; K.R.G. has a scientific investigator grant from Boston Scientific.
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