What is the role of stent placement in the treatment of nephrolithiasis?

Updated: Jun 21, 2018
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Answer

Internal ureteral stents form a coil at either end when the stiffening insertion guide wire is removed. One coil forms in the renal pelvis and the other in the bladder. Stents are available in lengths from 20-30 cm and in three widths from 4.6F to 8.5F. Some are designed to soften after placement in the body; others are rather stiff, to resist crushing and obstruction by large stones or external compression with occlusion from an extrinsic tumor or scar tissue.

To select the correct-size stent, estimates can be made based on the height of the patient, or the ureteral length can be measured. This is best performed by means of a retrograde pyelogram. The distance from the tip of the retrograde catheter to the ureteropelvic junction is measured in centimeters with a tape measure. To account for the average magnification effect of the film, 10% of this reading is subtracted. If the result is an odd number, a double-J stent one size longer is used. The most common lengths used are 26 cm in men and 24 cm in women.

The optimal stent width depends on both the relative diameter and course of the ureter and the purpose of the stent. If the patient has a stricture or a tortuous ureter, a stiffer or larger-diameter stent is placed if possible.

When used for stone disease, stents perform several important functions. They virtually guarantee drainage of urine from the kidney into the bladder and bypass any obstruction. This relieves patients of their renal colic pain even if the stone remains. Over time, stents gently dilate the ureter, making ureteroscopy and other endoscopic surgical procedures easier to perform later.

Because they are also quite radiopaque, stents provide a stable landmark when performing ESWL. A landmark is particularly important with small or barely visible stones, especially in the ureter, because the ESWL machine uses radiographic visualization to target the stone. However, routine stent placement should not be performed in patients undergoing ESWL, as there is no difference in stone-free rates with or without stent placement in these patients. [41]

Once large stones are broken up, stents tend to prevent the rapid dumping of large amounts of stone fragments and debris into the ureter (called steinstrasse). The stent forces the fragments to pass slowly, which is more efficient and prevents clogging.

Stents do have drawbacks. They can become blocked, kinked, dislodged, or infected. A KUB radiograph can be used to determine stent position, while infection is easily diagnosed by urinalysis. A renal sonogram can sometimes be helpful if obstruction is a concern.

Questionable cases can be evaluated further using a radiographic cystogram or an IVP. The cystogram is performed by filling the urinary bladder with diluted contrast media through a Foley catheter under gravity pressure. A stent that is unclogged and functioning normally should show free reflux of contrast from the bladder into the stented renal pelvis.

The major drawback of stents, however, is that they are often quite uncomfortable for patients due to direct bladder irritation, spasm, and reflux. This discomfort can be alleviated to some extent by pain medications, anticholinergics (eg, oxybutynin, tolterodine), alpha-blockers, and topical analgesics (eg, phenazopyridine).


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