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.
LESS-INVASIVE OPTIONS
Lithotripsy for small renal stones
Soon after it became available, lithotripsy became immensely popular because of its ability to break up stones without surgery. Ureteroscopic treatment has assumed a bigger role in recent years because it is more versatile, but lithotripsy remains the most common treatment for urolithiasis.
Advantages, uses. Lithotripsy is generally indicated for renal stones smaller than 2 cm,20 especially those not located in the calyx in the lower pole. It is most effective for stones in the renal pelvis (76% of patients become stone-free), and least effective for stones in the lower pole (59% stone-free).21 For this reason, for stones in the lower pole, only those smaller than 1 cm in diameter are treated with lithotripsy.
In the past, lithotripsy was also favored in patients who had stones in the proximal ureter, an area that was technically difficult to access with a ureteroscope. Recent advances in ureteroscope design have all but eliminated this difficulty.
Disadvantages. Lithotripsy can damage nearly any structure in the trajectory of the shock wave, causing bleeding, inflammation, or perforation. It can also cause disturbances in cardiac electrical signal transmission, leading to cardiac arrhythmias during treatment. Long-term concerns include a possible link between lithotripsy and the development of diabetes and hypertension.22 Lithotripsy is contraindicated in pregnancy and coagulopathic states and is less effective in morbidly obese patients.
Lithotripsy is more likely to fail if the skinto-stone distance is more than 10 mm, if the lower pole forms an acute angle with the ureter, or if the body mass index is greater than 30 kg/m2 (ie, if the patient is obese).23
Percutaneous nephrolithotomy for large or staghorn stones
Percutaneous nephrolithotomy is highly effective for renal calculi but is associated with more complications than lithotripsy or ureteroscopy. It involves inserting a needle through the skin into the renal collecting system and then dilating the tract to approximately 1 cm. Instruments are then inserted through this tract to break up and remove stones. In contrast to laparoscopy, no insufflation is used; the percutaneous tract provides direct access to the kidney for stone removal.
Advantages, uses. Outcomes of percutaneous nephrolithotomy are uniformly favorable across a wide spectrum of stone sizes, compositions, and locations.
Percutaneous nephrolithotomy is indicated in patients who have renal or ureteral stones larger than 2 cm or lower-pole stones larger than 1 cm (Figure 1).24,25
Staghorn stones, commonly associated with infection, lead to renal destruction with significant risk of morbidity and even death if left untreated.26 Because they must be completely removed, which is often difficult or impossible to do with ureteroscopy or lithotripsy, percutaneous nephrolithotomy is the first-line treatment.24
Disadvantages. Percutaneous nephrolithotomy is invasive and carries the associated risks of any major surgical procedure, including sepsis, perirenal hematoma or bleeding, and inadvertent injury to adjacent organs, including the pleurae, lungs, bowel, or spleen.
Ureteroscopy has improved
With improvements in design, stone treatment with flexible and semirigid ureteroscopy have become major options for urinary calculi, even those as far up as the kidney (Figure 1).
Advantages, uses. Ureteroscopy offers a low risk of complications (similar to that of lithotripsy), and stone-free rates approach those of percutaneous nephrolithotomy for small to moderate-sized renal stones.27,28 Outcomes are best for stones smaller than 1 cm, with residual fragments being seen with larger stones.
New flexible ureteroscopes that deflect up to 270° allow stones in the lower pole to be treated successfully.29 In conjunction with laser lithotripsy, ureteroscopy can be used to successfully treat hard stones (density > 1,000 Hounsfield units), stones in obese patients, and stones refractory to lithotripsy.
Rates of complications and second procedures are low, and, compared with lithotripsy, ureteroscopy takes less time to clear the stone.30 Ureteroscopy can also be used to treat stones in kidneys with complex anatomy, in which poor clearance of fragments may be a problem.28 It may also be used in coagulopathic, pregnant, or morbidly obese patients, in whom lithotripsy or percutaneous nephrolithotomy is less effective or contraindicated.
Disadvantages. Of note, ureteroscopy is a surgical skill, and better outcomes are obtained by surgeons with more experience.31
Complications of ureteroscopy include ureteral stricture, perforation, thermal injury, avulsion, intussusception, infection, or steinstrasse (obstruction with fragments of stones). In addition, after ureteroscopy, a temporary ureteral stent is often placed: the stent may cause discomfort and requires a minor adjunctive procedure for removal.
