Should Asymptomatic Renal Stones Be Surgically Treated? Pro-Observation

As radiologic imaging has become more ubiquitous over the years, incidental detection of asymptomatic renal stones is increasingly common. Urologists must then make the difficult decision to either surgically intervene or observe. However, there are no guidelines for the optimal management, largely because of the array of individual factors that may influence treatment decision making, and extensive patient counseling is often necessary. This review will summarize the current literature and provide factors to consider that support initial observation of asymptomatic renal stones over immediate surgical intervention.

First of all, what does choosing initial observation mean? Observation is an active treatment with routine follow-up and surveillance imaging to monitor for progression to symptomatic disease, stone growth, or obstruction. It emphasizes an individualized approach that allows for determination of the patient's natural history over time with routine imaging. Furthermore, directed preventative strategies, including both medical and dietary therapy, should be included with this approach, which may reduce stone growth or progression to symptomatic disease necessitating surgical intervention. Finally, choosing initial observation does not mean that you will never treat the stone. It is important to counsel the patient that the initial decision to observe does not preclude the option to later treat with surgery when appropriate.

The first consideration is that not all renal stones will become symptomatic or obstructing, which favors initial observation and avoids unnecessary morbidity from surgical intervention. Several studies describe the natural history of incidentally found asymptomatic renal stones, which helps to counsel patients on the risk of progression to symptomatic disease necessitating surgical intervention. Many of these studies report that the majority of patients will remain asymptomatic and only a small proportion eventually requires surgical treatment, supporting initial observation.

In 2018, Darrad and colleagues evaluated the natural history of asymptomatic caliceal renal stones and found that 59% remained on surveillance, 15% of stones passed spontaneously and 27% required surgical intervention for a median follow-up of 5.3 years (N = 301 renal units). ¹ Similarly in 2015, Dropkin and colleagues performed a retrospective review of 160 nonobstructing asymptomatic renal stones among 110 patients conservatively managed with surveillance imaging. ² During the average follow-up of 3.4 ± 1.6 years, most remained asymptomatic, with 7% of stones passed spontaneously and only 20% progressed to symptomatic disease necessitating surgical intervention. ² They found that stone location predicted stone progression, with spontaneous passage more likely for non-lower pole stones compared with lower pole stones (15% vs 3%, p = 0.016) or to become symptomatic necessitating surgical intervention (41% vs 24%, p = 0.047). ²

Additional studies reported similar low surgical intervention rates (7%–26%) in patients who initially chose observation with routine surveillance imaging. ³ Moreover, a recent meta-analysis of 13 studies on asymptomatic renal stones from Han and colleagues concluded that longer follow-up did not correlate with an increase in surgical events for a surveillance period of 0.9–6.7 years (r = 0.01, p = 0.98). ³ These studies highlight that in a properly counseled patient, observation is a practical option that should include routine imaging to evaluate for stone progression or silent obstruction, an approach supported by both American Urological Association and European Association of Urology guidelines. The low occurrence of progression to surgical intervention with this conservative approach would argue that it is the better option to initially observe and monitor over time. It is also important to consider that many of these studies did not report whether patients had undergone metabolic evaluation and medical/dietary therapy for prevention of stone growth. As discussed previously, the decision to observe should also include a focus on stone prevention.

The next consideration is that there is no cookie cutter formula, as not all patients are the same, and we should focus on an individualistic approach. There are certain patient factors in which observation with routine surveillance is favorable for asymptomatic renal stones; for example, advanced age, poor functional status, comorbidities that portend poor surgical outcomes, or pregnancy. If an active problem develops in these cases, then it becomes easier to accept the higher risk of surgery and associated morbidity. In addition, individual patient goals of treatment may also vary, which may be based on numerous factors, including previous experience, stone history, job status, access to care, financial concerns, and childcare.

In certain cases, there are anatomical or stone features in which one may favor observation with routine surveillance for asymptomatic renal stones; for example, caliceal diverticulum or stenotic infundibulum, stone stability on imaging, lower pole location, small stone size, and nonobstructing. Observation may be favorable for asymptomatic caliceal diverticular stones as there is no risk of spontaneous passage; however, there is no literature supporting this strategy. Largest stone diameter determines the likelihood of spontaneous passage, and certainly for stones ≤5 mm observation would be the optimal choice given the high rate of spontaneous passage should the stone progress to the ureter. Stone growth rate may also be an important factor, although this is not well studied. For instance, it should be recommended to continue observation if a stone took 10 years vs 6 months to grow 1 mm, despite the overall stone size. Routine imaging will provide an individualistic natural history and stability in an asymptomatic patient should favor continued observation. Another important consideration is stone location. The majority of incidentally detected renal stones are located in the lower pole, and have reduced rates of spontaneous passage or progression to symptomatic disease. ² Inci and colleagues prospectively evaluated asymptomatic lower pole renal stones (mean size 8.8 mm) in 24 patients for an average follow-up of 4.4 years. ⁴ They reported one-third of patients had stone progression with only one-third of cases necessitating surgical intervention (overall rate of 11%). ⁴

An additional factor to consider is that, despite best attempts to render patients stone free with surgical intervention, there is a high rate of residual fragments, which may leave patients with a similar predicament. Using computerized tomography for postoperative imaging, Rippel and colleagues reported a 38% risk of residual fragments (≥2 mm) after ureteroscopy (URS). ⁵ Portis and colleagues found that stone-free rates are even lower (54%) when using strict criteria of 0 mm for residual fragments. ⁶ These residual fragments may have future consequences, as Iremashvili and colleagues found that the larger the residual fragment the higher the risk of repeat surgery. ⁷ Of 781 patients who underwent URS, 161 required repeat surgery in the same kidney during a median follow-up of 4.2 years. ⁷ In addition, we should consider that there may be a higher risk of adverse stone events in patients with asymptomatic residual fragments after surgical intervention compared with those with untreated asymptomatic renal stones.

Several randomized controlled trials (RCTs) have been done to compare surgical intervention with observation. Yuruk and colleagues randomized patients with asymptomatic lower pole renal stones (<2 cm in diameter) to percutaneous nephrolithotomy (PCNL), extracorporeal shockwave lithotripsy (SWL), or observation. ⁸ At 3 months follow-up they reported a stone-free rate of 97% for PCNL, 55% for SWL, and 0% for observation (p < 0.05). ⁸ With 22% of patients in the observation group progressing to surgical intervention. ⁸ More recently, Sener and colleagues randomized patients with single asymptomatic lower pole renal stones (<1 cm in diameter) to observation, SWL, or URS. ⁹ They reported a stone-free rate of 90% for SWL (average 1.5 ± 0.7 sessions) and 92% for URS. ⁹ With a minimal risk (12%) of the observation group developing stone progression with either symptomatic disease or stone growth during the 2-year follow-up; they concluded that observation, SWL, or URS are all suitable treatment options. ⁹ Furthermore, a previous RCT for small asymptomatic renal stones (<1.5 cm in diameter) were randomized to observation or SWL and during the 2-year follow-up they reported no differences in stone-free rates, need for reintervention, or health-related quality of life. ¹⁰ With no guarantee that surgery will render patients completely stone free, these studies highlight the importance of counseling them about the risk of residual fragments and the potential need for reintervention.

The last consideration is that there is also no guarantee that the surgery will be without complications. Initial observation for asymptomatic renal stones avoids unnecessary surgery and morbidity. It is unlikely to make an asymptomatic patient feel better; therefore, the stakes are much higher with surgical intervention on this population. Complications can lead to prolonged stent times, emergency department visits or hospitalizations, repeat surgical intervention, and higher economic burden, for example. Morbidity may be more acceptable in a symptomatic patient because often in the end, the patient is ultimately better after intervention. In the asymptomatic patient it is extremely important to carefully consider the morbidity of surgery, weighing the risks and benefits with the patient's goal in mind.

In the end, shared decision making with patients is the key and assessment of patients' preferences is exceedingly important for treatment decisions in asymptomatic patients. As health care has shifted to more patient-centric care, it is also important to shift our approach to the treatment of asymptomatic renal stones. An individualistic approach should be taken, which favors initial observation and more selective surgical intervention only when necessary. The shared decision-making process involves adequately counseling patients, which will set expectations to ensure that patients' goals are met. Furthermore, one should always consider quality of life and discuss the goals of treatment, as it may be complex for certain individuals especially those with comorbidities that portend poor surgical outcomes. However, patients frequently want their physicians to ultimately decide on the best treatment.

In summary, with extensive patient counseling, observation with routine follow-up imaging and preventative measures is the better option over immediate surgical intervention for asymptomatic nonobstructing renal stones. Observation is fluid, allowing for the strategy to change and intervene with surgery when appropriate. This strategy avoids unnecessary surgery and morbidity. With the risks of residual fragments after surgical intervention and associated morbidity, it becomes more important to carefully weigh the risks and benefits in the asymptomatic patient. Initial observation is patient-centered and determines the individualized natural history over time, as many patients will not progress to symptomatic disease necessitating surgical intervention. A variety of relevant patient and stone factors should be considered, however ultimately a shared decision-making approach should be taken with an emphasis on patient preference and initial observation should be considered for asymptomatic renal stones.