Less-invasive ways to remove stones from the kidneys and ureters
ABSTRACTLess-invasive interventions for upper tract urolithiasis are extracorporeal shock-wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy. Each has advantages and disadvantages, depending on the location, size, and composition of the stone and on the patient’s renal anatomy, body habitus, and comorbidities.
KEY POINTS
- Stones that obstruct the flow of urine or that are associated with infection (ie, struvite or “staghorn” stones) should be removed promptly.
- For small stones in the distal ureter, medical therapy is an option: pain control, hydration, and control of ureteral spasms with calcium channel blockers and alpha-blockers help the patient pass the stone spontaneously.
- Extracorporeal shock-wave lithotripsy is the mostly commonly used option, but it is less effective for large stones and in obese patients.
- The ureteroscope can now be used to extract stones as high up as the kidney. Catheters that contain lasers and lithotripsy devices can break up large stones in situ for removal.
- Percutaneous nephrolithotomy is very effective for large stones in the kidney and is especially indicated for struvite stones.
FACTORS THAT AFFECT THE CHOICE OF TREATMENT
Size and location of the stone
The most important predictors of spontaneous passage of ureteral stones are size and location. In general, small stones are more likely to pass spontaneously than large ones, and distal stones are more likely to pass than stones more proximal in the urinary tract.
Stones are typically classified as either ureteral (proximal, middle, or distal) or renal (pelvic or calyceal), depending on their location.
In the ureter. Most ureteral stones smaller than 5 mm in diameter pass spontaneously within 4 weeks of the onset of symptoms.25,32 In patients who have stones smaller than 1 cm, whose pain is controlled, and who show no evidence of sepsis or renal insufficiency, a period of observation is a reasonable option.11 Medications such as tamsulosin (Flomax) and nifedipine have been shown to reduce the need for analgesia and to reduce the time to stone passage.33,34
Lithotripsy and ureteroscopy are the two primary interventions for ureteral calculi.
Regardless of size, stones in the ureter can usually be removed by ureteroscopy. This may involve laser or pneumatic lithotripsy within the ureter or simple ureteroscopic basket retrieval of the intact stone. In situ lithotripsy is an option for proximal ureteral calculi and may be favored by patients who wish to avoid placement of a ureteral stent at the time of intervention. Percutaneous nephrolithotomy is reserved for large (> 2-cm) or impacted proximal ureteral stones, or for cases in which ureteroscopy has failed.35
For stones in the proximal ureter, no difference has been shown in stone passage rates between lithotripsy and ureteroscopy. For proximal stones smaller than 1 cm, lithotripsy has a higher stone-free rate, and for stones larger than 1 cm, ureteroscopy has been shown to have superior stone-free rates.11
For mid-ureteral and distal ureteral stones of all sizes, ureteroscopy has been shown to have superior stone-free rates, although the difference is statistically significant only for distal stones.11
In the kidney. Large renal stones (> 2 cm) or staghorn calculi within the renal collecting system are best treated with percutaneous nephrolithotomy, whereas renal stones smaller than 1 cm can usually be treated ureteroscopically or with lithotripsy.
Stones within the renal collecting system measuring between 1 and 2 cm in diameter can be treated with ureteroscopy, lithotripsy, percutaneous nephrolithotomy, or a combination, depending on the location and composition of the stone and the wishes of patient.
Stone composition
Cystine stones and calcium oxalate stones are hard, with a density greater than 1,000 Hounsfield units. Lithotripsy has a high failure rate with these types of stones.36
Uric acid stones are softer and do not show up well on x-ray imaging. While it is technically feasible to perform lithotripsy under ultrasonographic guidance, most practitioners prefer to use fluoroscopy to locate the stone. For this reason, patients with radiolucent stones (ie, uric acid stones) are also not good candidates for lithotripsy.
Struvite (staghorn) stones are by definition infected, with bacteria residing within the stone itself. Thus, it is imperative to remove all stone fragments during treatment to prevent sepsis and stone reformation. Over time, an untreated staghorn calculus will lead to failure of the renal unit.
Although lithotripsy, ureteroscopy, and percutaneous nephrolithotomy can all be used to treat staghorn calculi, percutaneous nephrolithotomy has the best stone-free rate (78%), and lithotripsy has the lowest (54%).24 Therefore, percutaneous nephrolithotomy is recommended as the first treatment for these stones, and if combination therapy is used, then percutaneous nephrolithotomy should be done last to ensure that the stone is completely removed.24 If lithotomy is to be used, drainage of the renal unit must be done in advance with either percutaneous nephrostomy or a ureteral stent, to ensure that all infected stone fragments will be flushed out.24
PREVENTING RECURRENCES
Metabolic abnormalities that increase the risk of urolithiasis can be identified and treated in up to 95% of patients who form recurrent stones.37 Most of these patients require simple dietary modifications, and just 15% require pharmacotherapy. (For more on this topic, see the review by Dr. Phillip Hall in this issue of the Journal.38) As urolithiasis is common and often recurrent, the appropriate interventive management, combined with dietary prophylaxis, should minimize patient morbidity and preserve renal function.
