Stent is defined as a “thread, rod or a catheter that is lying within a tubular structure, which provides support and assures the patency of an intact but contracted lumen”. Urethral stents are usually made up of metal, polymeric or biodegradable materials. These stents are usually rigid enough to maintain the patency of urethral canal.
What is the anatomy of the urethra?
Urethra is a hollow tube that connects bladder to the outside. Urethral sphincter is situated just outside the bladder, which controls the urine outflow. Male urethra is longer than females. In addition it passes through various structures such as the prostate gland. This makes it more vulnerable for constriction.
What are the indications of urethral stent placement?
Urethral stents help to maintain patency of urethra. Therefore stents are surgically or endocopically placed in conditions where it can become narrow (bladder outlet obstruction). In addition urethral stents can be placed temporary or permanently.
What are the causes of bladder outlet obstruction that need stent placement?
Benign prostatic hyperplasia
In males urethra passes through the prostate gland. Therefore, enlarged prostate gland can cause urethral obstruction and urinary retention. This is a common cause for bladder outflow obstruction, especially in elderly people. However, urethral stenting is indicated only when the patient is not suitable for surgical removal of the prostate gland.
Prostate cancer
Locally advanced prostate cancer is another indication for the urethral stent placement. Sometimes prostate cancer can invade into the urethra and cause urethral strictures.
Neurogenic bladder
Neurogenic bladder occurs in people with spinal cord injuries. This can disrupt nerve supply to the bladder and urethral sphincter. However, smooth muscles in bladder can contract even without nervous stimulation, when it is full. But nerve supply is needed for the relaxation of the urethral sphincter. Therefore, this can cause urinary retention and it can be prevented by placing a urethral stent.
Another indication is urethral stricture disease. A common cause for urethral stricture disease is urethral trauma.
What are the contraindications?
There are several contraindications for the urethral stent placement. Most common contraindication is infection of the urethral tract. Acute prostatitis or inflammation of the prostate gland is another contraindication for urethral stents. In addition acute lower urinary tract infections and bladder infections are contraindications.
Surgeons may not insert a urethral stents in bladder stones, strictures involving the penis, strictures involving the external urethral sphincter and in recurrent tumors that affects the urethra.
To detect these contraindications, the surgeons may perform various medical tests such as retrograde or anterograde urethrography, MRI scans, uroflowmetry, videourodynamic studies and cystoscopy. In addition, urine culture and urinalysis are performed to rule out possible urine infection.
Summary
Urethral stents are used to support and assure patency of the urethral tract. They are inserted surgically for various conditions that can cause urine outflow obstruction. However, urethral stent placement is contraindicated urinary tract infections, urinary stones, strictures involving penis and in strictures involving external urethral sphincter.
Sources and further reading
Urethral stents: Review of technology and clinical applications by Mordechai Duvdevani , Ben H.Chew and John D.Denstedt
