Approach to Small, Nonobstructing Renal Calculi

Small renal calculi are often asymptomatic and incidentally detected on imaging modalities during the workup of other medical conditions. While the treatment approach is clearer for symptomatic and larger renal calculi, managing smaller and lower-burden stones depends on patient history, imaging, and laboratory studies. Although most nonobstructing small renal stones are asymptomatic, they may still progress to become symptomatic either due to infection or obstruction in up to one-third of cases.¹ While small nonobstructing stones have commonly been actively surveilled, recent literature shows that their removal results in a lower incidence of future complications of up to 82% compared to stones that are not removed.² Therefore, patients with small renal stones should be aware of all management options when presenting to the clinic.

Common Treatment Options

For patients who seek treatment for their small, nonobstructive renal stones, the 2 contemporary treatment options are ureteroscopy (URS) and extracorporeal shock wave lithotripsy (ESWL). While studies have shown that URS may be more effective than ESWL as an initial approach to achieving a stone-free outcome, URS commonly includes ureteral stent placement. Stents have several well-known complications, including increased rates of hematuria, irritative urinary symptoms, infection, and dysuria. In contrast, studies have shown that stents have no benefit and are therefore not needed for patients undergoing ESWL, especially if the stone is small (<15 mm).³

Lastly, URS involves general or spinal anesthesia, unlike ESWL, which can be done with intravenous sedation or even local anesthesia.⁴ Thus, while both are reasonable treatment options for small, nonobstructive stone removal, ESWL may be a better option for patients who prefer a less invasive outpatient procedure without stent placement (Figure 1).

Outcomes of ESWL

ESWL can break up stones anywhere in the urinary tract but is guideline recommended as first-line treatment for stones in the kidney or upper ureter.³ Contemporary lithotripters can fragment most stone types with low-risk, short recovery periods, and low analgesic use. Postoperative flank pain typically presents as soreness lasting 1 to 2 days. Patients may also experience self-limited hematuria. More rarely, there is a risk of hematoma.^3,5 Other documented complications, including infection, obstruction, altered kidney function, and hypertension, are even more rare, and much of the literature is outdated.⁶

Recent studies estimate the initial success rate of ESWL after one visit to be 69%, with a success rate of up to 93% after repeated treatment.⁷ However, the success of ESWL may be higher depending on the stone composition, size, and the urologist’s experience with the procedure (Figure 2). For patients with smaller stone sizes < 10 mm, studies have shown success rates up to 99% after initial treatment.⁸ Thus, while URS may result in higher single-session stone-free rates, ESWL remains an effective option for patients with small asymptomatic stones who wish to minimize surgical side effects.

It should be noted that ESWL is generally contraindicated in pregnancy, active anticoagulation, untreated coagulopathies, and aneurysms due to risks of bleeding, although the current literature has mixed opinions on the latter.⁹

Tips for Improving ESWL Outcomes

ESWL is most successful in patients with small, less dense stones (<10 mm and <1500 Hounsfield units) and skin-to-stone distances < 15 cm. While there is increased clearance of upper and interpolar stones, lower pole stones < 15 mm diameter show clearance after one procedure. Urologists should consider anatomical location and renal abnormalities, such as large renal cysts near the stone or kidney malrotations, as in the case of horseshoe kidney, which may impact stone clearance. Additionally, stone composition should be considered, as cystine and denser calcium oxalate monohydrate stones may be less favorable. Finally, uric acid stones are often not visible on fluoroscopy; patients with these stones should be counseled on adjustments that may be necessary to the procedure or urged to consider URS.¹⁰

Conclusion

Current literature has shown that the removal of small, asymptomatic renal calculi may decrease rates of future complications such as renal colic and growth of secondary stones. Patients seeking treatment for small, nonobstructing kidney stones should be properly educated on the outcomes and complications of both URS and ESWL. ESWL continues to be an attractive treatment option. It is the only truly noninvasive kidney stone treatment and presents a safe and effective option for patients seeking an outpatient procedure without stent placement.

Conflict of Interest Disclosures: Dr Scotland reported being a consultant for Storz Medical and an advisor for Advanced MedTech.