A ureteral stent is a thin, flexible tube threaded into the ureter to help urine drain from the kidney to the bladder or to an external collection system.
Urine is normally carried from the kidneys to the bladder via a pair of long, narrow tubes called ureters (each kidney is connected to one ureter). A ureter may become obstructed as a result of a number of conditions including kidney stones, tumors, blood clots, postsurgical swelling, or infection. A ureteral stent is placed in the ureter to restore the flow of urine to the bladder. Ureteral stents may be used in patients with active kidney infection or with diseased bladders (e.g., as a result of cancer or radiation therapy). Alternatively, ureteral stents may be used during or after urinary tract surgical procedures to provide a mold around which healing can occur, to divert the urinary flow away from areas of leakage, to manipulate kidney stones or prevent stone migration prior to treatment, or to make the ureters more easily identifiable during difficult surgical procedures. The stent may remain in place on a short-term (days to weeks) or long-term (weeks to months) basis.
Chronic blockage of a ureter affects approximately five individuals out of every 1,000; acute blockage affects one out of every 1,000. Bilateral obstruction (blockage to both ureters) is more rare; chronic blockage affects one individual per 1,000 people, and acute blockage affects five per 10,000.
The size, shape, and material of the ureteral stent to be used depends on the patient’s anatomy and the reason why the stent is required. Most stents are 5-12 inches (12-30 cm) in length, and have a diameter of 0.06-0.2 inches (1.5-6 mm). One or both ends of the stent may be coiled (called a pigtail stent) to prevent it from moving out of place; an open-ended stent is better suited for patients who require temporary drainage. In some instances, one end of the stent has a thread attached to it that extends through the bladder and urethra to the outside of the body; this aids in stent removal. The stent material must be flexible, durable, non-reactive, and radiopaque (visible on an x ray).
The patient is usually placed under general anesthesia for stent insertion; this ensures the physician that the patient will remain relaxed and will not move during the procedure. A cystoscope (a thin, telescope-like instrument) is inserted into the urethra to the bladder, and the opening to the ureter to be stented is identified. In some instances, a guide wire is inserted into the ureter under the aid of a fluoroscope (an imaging device that uses x rays to visualize structures on a fluorescent screen). The guide wire provides a path for the placement of the stent, which is advanced over the wire. Once the stent is in place, the guide wire and cystoscope are removed. Patients who fail this method of ureteral stenting may have the stent placed percutaneously (through the skin), into the kidney, and subsequently into the ureter.
A stent that has an attached thread may be pulled out by a physician in an office setting. Cystoscopy may also be used to remove a stent.
A number of different technologies aid in the diagnosis of ureteral obstruction. These include:
- Cystoscopy (a procedure in which a thin, tubular instrument is used to visualize the interior of the bladder)
- Ultrasonography (an imaging technique that uses high-frequency sounds waves to visualize structures inside the body)
- Computed tomography (an imaging technique that uses x rays to produce two-dimensional cross-sections on a viewing screen)
- Pyelography (x rays taken of the urinary tract after a contrast dye has been injected into a vein or into the kidney, ureter, or bladder)
Prior to ureteral stenting, the procedure should be thoroughly explained by a medical professional. No food or drink is permitted after midnight the night before surgery. The patient wears a hospital gown during the procedure. If the stent insertion is performed with the aid of a cystoscope, the patient will assume a position that is typically used in a gynecological exam (lying on the back, with the legs flexed and supported by stirrups).
Stents must be periodically replaced to prevent fractures within the catheter wall or build-up of encrustation. Stent replacement is recommended approximately every six months; more often in patients who form stones.