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John Bidmead and Professor Linda Cardozo of Kings College Hospital, London, discuss how injections into the urethra wall can help women with stress incontinence.
Introduction
The injection of bulking agents around the urethra and bladder neck as a treatment for stress incontinence has aroused a great deal of interest. The material most commonly used is collagen but a number of others are available or under development. As is often the case, high expectations were raised for this technique. Experience has shown that, while it is a useful treatment, it is not suitable for all women. This article aims to explain how the procedure works, how it is performed and where it may be most useful.
Despite a great deal of research over many years, the exact cause of stress incontinence is not fully understood. The ability of the bladder and urethra to prevent leakage of urine during coughing, sneezing and exercise appears to rely on two different mechanisms.
The first is the support of the bladder and urethra by the pelvic floor muscles, and the ligaments and connective tissues surrounding the bladder base. These help to provide support during times of physical exertion and may be damaged during pregnancy and childbirth, or weakened by age or heavy exercise, leading to the development of stress incontinence.
The second mechanism preventing leakage of urine is the watertight seal provided by the urethra itself. This is maintained by a combination of the circular sphincter muscle, surrounding and compressing the urethra, and by the rich network of blood vessels beneath the inner lining of the urethra, which helps to provide a spongy, waterproof seal. These structures may also be damaged or weakened by pregnancy, childbirth and ageing, or damaged by scarring from surgery or radiotherapy.
The most important of these two mechanisms in women with straightforward stress incontinence appears to be loss of the support of the bladder and urethra. For this reason, most treatments aim to improve this. Physiotherapy acts to increase the strength and support given by the pelvic floor muscles. Most surgical operations for stress incontinence are based on lifting and re-supporting the bladder and urethra. Operations such as colposuspension, "sling" procedures, "needle-suspensions" and vaginal repair operations are all designed to work mainly in this way.
The injection of materials close to the urethra and its opening into the bladder provide pressure to help restore the seal of the urethra and improve its watertight nature, and have no effect on the support of the bladder itself. This is not a new idea, almost a hundred years ago an injection of phenol, an irritant, was tried. The resulting scarring
may have helped narrow the urethra and cured some women but the high complication rate meant that this technique was quickly abandoned.
More recently, a number of different substances have been used, much more successfully. Teflon paste was introduced in the 1970s. This gave good and quite long-lasting results but there were problems with excessive scarring and migration of Teflon particles to other tissues in the body, and it is no longer used.
Fat, removed from beneath the woman’s own skin may be used for injection. It is cheap and easy to obtain and, as it comes from the woman herself, there is no worry about infection. Unfortunately, the results appear very short lasting, the fat cells quickly disperse and, for this reason, this technique is rarely employed.
Collagen (GAX collagen, Contigen) has been widely used for a number of years. It is produced from the cartilage of cattle from the USA, which is extensively processed and sterilised to produce a viscous paste. There is no risk of Bovine Spongiform Encephalopathy (BSE) transmission due to the processing which would destroy any bacterial or viral particles.
A paste made from microscopic particles of silicon suspended in a viscous gel (Macroplastique) is also currently used. A number of other materials have been introduced recently or are under development with the aim of improving the long-term results of this technique. These include carbon-fibre-coated beads, ceramic paste, and micro-balloons.
How the Operation is Performed.
Injection of all the periurethral bulking agents is performed in a similar way. The procedure is quick, taking 15 to 20 minutes. No incisions are made and this means that it may be carried out with local anaesthetic or under a regional anaesthetic such as an epidural. Some surgeons and women prefer a short general anaesthetic. Using a fine fibreoptic cystoscope the inside of the urethra and bladder can be inspected and a fine needle guided to inject the material at exactly the appropriate spot. Usually three injections are made around the urethra. The exact amount used depends on the material used and how much closure of the urethra the surgeon feels is required.
As the operation is short and there is little discomfort afterwards it is possible for women to go home the same day. Some units prefer women to stay overnight to check that there are no problems with bladder emptying. Either way, recovery from the operation is very quick.
Complications
In general, this technique has very few major complications. Urinary tract infection is common in up to a fifth of women having periurethral injection, but can usually be quickly and easily treated with a course of antibiotics. Difficulty urinating immediately after surgery is a problem with all operations around the bladder and urethra due to swelling and bruising of the tissues. This is a relatively uncommon problem after periurethral injection but may occur. This usually settles quickly but may require catheterisation for a short time while any swelling subsides. Long term problems are very rare.
Results of Periurethral Injection
Given that this technique is so quick and easy with very few complications, it would appear to be an ideal treatment for stress incontinence. Unfortunately, the problem lies with the longer-term results. In the short term, within three months after injection, the
results are good with at least 80% of women cured or improved. As time goes on, however, the results become poorer.
After two years, less than half of these women will still be cured. Longer-term studies of the currently used materials are still underway but it is likely that the results will follow this trend, becoming poorer still as time goes by. This is due to the material injected dispersing away from the urethra over time.
As the technique is relatively quick and easy, injections can be repeated and indeed some women may require more than one injection before they are cured. It is not clear at this time which material is longest lasting: fat seems to be absorbed very quickly, GAX collagen and Macroplastique persist for much longer. Newer materials under development may improve these results.
The results in younger, more physically active women are less good and overall last for a shorter time. While it may appear tempting to simply give repeated injections every so often, the materials for injection are very expensive and the long-term effects of repeated injections are unknown. It is probably more sensible to opt for one of the alternative operations if long term cure of stress incontinence is the aim. It has also been suggested that periurethral injection may be suitable for women who intend to have further children. There is little evidence to support this and, as the effect of injection on the success of further surgery is unknown, it is the policy in our unit to advise deferring definitive surgery until a woman has completed her family.
It was also thought that this technique would be suitable for women with a combination of stress incontinence and detrusor instability (an "overactive" or "unstable" bladder). Conventional surgery is less effective in such cases unless drugs are prescribed to treat the detrusor instability. It had been hoped that injections would be more suitable for this group of women as there is less interference with the tissues of the bladder. This appears not to be the case and great care needs to be taken before considering any surgery in women with "mixed incontinence" (a combination of stress incontinence and detrusor instability).
The poorer long-term effects of periurethral injections in general do not mean that they are not suitable for some women, however. As the operation is relatively minor it may suit older women who are less fit for more complicated surgery. The long-term results in older women who are less physically active also tend to be much better.
Periurethral injection is particularly suitable for women who have had previous surgery or radiotherapy when the urethra and bladder are surrounded and fixed by scar tissue. In this situation, conventional surgery may be difficult and less likely to succeed and so
injectables can be the ideal treatment. Complete cure may not be achievable for some women in this group, but the majority report substantial improvement in their symptoms. In a carefully selected group of women such as these, the longer-term results of injectables may be acceptable and repeated injections given over periods of time may be appropriate in this group to maintain the improvement in symptoms.
Conclusions
The injection of periurethral bulking agents is a technique that is quick and easy to perform with a low complication rate and rapid recovery. Due to the poorer long-term results in young active women, it is probably not suitable for more widespread use and conventional procedures may be more appropriate. However, in women who are less fit, or where conventional surgery is unsuitable, it remains a very valuable technique.
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