The common use of ureteral stents has greatly increased since the 19th century, when Gustav Simon first placed a tube into the ureteral opening during an open cystostomy. Ureteral stents are primarily used to support internal upper urinary tract drainage, especially in cases where healing is required. Such uses for stents occur in cases of urinary obstruction from nephrolithiasis, as well as obstruction from external malignancies. Stents can also be placed after surgery involving the urinary tract, as adjunctive therapy to extracorporeal shock-wave lithotripsy (ESWL), or in cases involving trauma to the ureter. Ureteral stents have radiopaque markers and are constructed from polymers, such as polyethylene, C-flex and polyurethane, and silicone, which are flexible and resist encrustation with mineral deposits to varying degrees. Stents employ various shapes at one or both ends to help anchor the stent in the renal pelvis and/or bladder, and prevent migration. The shapes most commonly used are "J" curves or pigtail loops.5
In patients with nephrolithiasis, stones that do not pass are often treated with ESWL, and adjunctive ureteral stents are often used to assist in urine flow and passage of stone fragments. In response to the presence of the stent, the ureter often dilates, allowing for extraluminal as well as intraluminal flow of urine and stone debris. 6 For larger stones and remaining fragments, stents may remain in for further treatment with ESWL. In nephrolithotomy or other open procedures for the removal of stones, stents are used to decrease the urinary leakage that commonly occurs.
Ureteral stents may relieve obstruction caused by primary or metastatic carcinomas, as well as other pathology (for instance, ureteral fibrosis) that leads to mechanical obstruction. Stents are also used in many surgical and percutaneous procedures involving the upper urinary tract, including nephrolithotomy and percutaneous nephrostomy tube insertion. Easily removable stents assist in maintaining a consistent lumen and outlet for urine, especially in surgical anastomoses of the ureter. Complications from a variety of surgical procedures can result in iatrogenic injury to the ureter, where stents may again be used. In fact, to offset obstruction that may be caused by any resultant ureteral edema, stents are often left indwelling for a period of 24 h after ureteroscopy. 7 Further, any other traumatic injury to the upper urinary tract may call for the use of an ureteral stent to help maintain ureteral patency and/or urinary drainage.
Ureteral stents may remain in place for weeks to months and often function without complication. However, stents can become encrusted with mineral deposits, depending on the length of time a stent has been in place, the characteristics of the stent itself, and the chemical composition of the urine. Encrustation can be minimized by keeping the urine at an acidic pH, uninfected, and dilute, with patients being instructed to maintain fluid intake of at least 2 L/day. Limited encrustation is not in itself an emergency, since dilation of the ureter often allows urine to flow around the stent, thus bypassing an obstructed lumen. Complete obstruction of urine flow is possible, although this tends to occur more often in patients with long-term stents. These patients typically require urologic consultation and in some cases may require stent replacement. In patients who received ureteral stents to treat obstruction from malignancy, 46 to 53 percent fail to drain properly, whereas those stents used as adjunctive therapy for renal stones have a much higher success rate.
Although peristaltic movements of the ureters stop with the placement of the ureteral stent, respiratory movements of the kidneys do not. These movements can result in migration of the stent, either upward toward the kidneys or downward into the bladder. Upward migration can lead to renal injury, obstruction and, in cases of infection, septicemia. Correction may entail pyelotomy, nephrostomy drainage and even, in extreme cases, nephrectomy. Changing abdominal or flank pain, or bladder discomfort, may be indicative of stent migration. X-ray examination is indicated to evaluate stent position, and urologic consultation with further studies may eventually be necessary.
Placement of the ureteral stent itself initiates a foreign-body reaction and can predispose patients to an increased risk of urinary tract infection—up to a 7.5 percent incidence of positive urine cultures in patients with stents. Studies have shown that a higher rate of UTI exists as long as 1 month after the removal of the stent. When a UTI does occur, stent removal is not mandatory, because most infections can be managed with outpatient antibiotics. If pyelonephritis or systemic infection is evident, however, then further evaluation and emergent intervention are indicated. Plain x-ray examination and urologic consultation for evaluation of stent migration/malfunction are indicated. Antibiotic therapy should also be initiated in a timely manner.
Dysuria, urinary urgency, frequency, and abdominal and flank discomfort are common complaints in patients with ureteral stents. The use of analgesics and anticholinergics provides some relief. In some extreme cases, though, a few days of belladonna and opiate suppositories may be effective. The baseline discomfort in a functioning, well-positioned stent can range anywhere from minimal to debilitating. In some cases, the pain may be so great as to necessitate removal of the stent. However, an abrupt change in the character, location, or intensity of the pain requires further evaluation for stent malposition/malfunction. Along with these irritative symptoms, asymptomatic microscopic hematuria is often present, though clinically insignificant. Gross hematuria, with or without clots, may be the result of stent erosion through a segment of the urinary tract, stent migration, or the passage of a renal stone and requires further investigation, including urologic consultation.
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