A fistula is an abnormal, tube-like connection that forms between two organs or vessels that are lined with epithelial cells. Fistulas are generally the result of a disease condition, but artificial fistulas may also be surgically created for therapy.
Examples of naturally occurring fistulas are those that form between the end of the bowel and skin near the anus (anal fistula) or between the intestine and the vagina (enterovaginal fistula). Fistulas may also form between the rectum and the vagina and this is called a rectovaginal fistula. Although fistulas are usually caused by injury or surgery, they may also form after an infection has led to severe inflammation. Inflammatory bowel conditions such as Chron’s disease and ulcerative colitis are examples of conditions that lead to fistulas forming between two loops of the intestine.
An artificial fistula may be created, for example, between an artery and vein (arteriovenous fistula) when a person needs renal dialysis. An arteriovenous fistula may also be caused by an injury.
Fistula structure
Some common types of fistulas include:
- A blind fistula which forms a tube that opens only at one end and is closed at the other. These may turn into complete fistulas if left untreated.
- An incomplete fistula, which has only an external opening.
- A complete fistula which has two openings, one of which is internal and the other external.
- A horseshoe fistula describes a U-shaped connection formed between two external openings on both sides of the anus.
Anal fistula
When a fistula forms between the anal canal and skin near the anus, bleeding, pain and discharge may occur when a person passes stools. Other possible symptoms of an anal fistula include swelling, tenderness, redness surrounding the anus, constipation and fever. A fistula may develop after a patient has undergone surgery to drain an anal abscess. In some cases, the fistula leads to persistent drainage and in other cases, recurrent anal abscesses may occur if the outside of the channel opening closes.
Anal fistulas can usually be diagnosed based on a digital rectal examination, but in some cases, further tests may be required. These additional tests may be carried out to check for the presence of diverticular disease, rectal cancer, sexually transmitted disease and inflammatory bowel disease. The only way to resolve an anal fistula is via surgery. Various different forms of surgery are available depending on the position of the fistula and some of these procedures are described below.
Fistultomy
This is the procedure used in the majority of fistula cases. The whole fistula is cut open lengthwise and the contents flushed out by the surgeon. The surgical wound heals after one or two months.
Advancement flap
In cases of complex fistula or a high risk of incontinence, a piece of tissue is removed from the rectum or skin near the anus, which is referred to as an advancement flap. When the fistula tract is surgically removed, the flap is attached to where the fistula opening was.
Fibrin glue
This non-surgical method involves the injection of glue into the fistula, which seals the tract. The opening is then closed using stitches. Although the procedure is safe and simple, the long term effectiveness is poor, with success rates dropping from 77% initially to around 15% after 16 months
Vaginal fistula
A vaginal fistula may form between the vagina and another body part such as the colon (colovaginal fistula), rectum (rectovaginal fistula), the small intestine (enterovaginal fistula) or the bladder (vesicovaginal fistula). The fistula may form as a result of injury, surgery, infection or radiotherapy.
A vaginal fistula is often diagnosed based on a pelvic exam, medical history and the presence of risk factors such as pelvic radiotherapy or recent pelvic surgery. Additional tests may also be performed such as cystoscopy, a dye test, a fistulogram, computerized tomography and magnetic resonance imaging.
Vaginal fistulas usually require surgery, although some nonsurgical treatment options can sometimes be effective. If the patient has a simple rectovaginal fistula, for example, they may only require dietary changes and fiber supplements to increase the bulk of their stool. When surgery is needed, it is performed through the abdomen or vagina, depending on the location of the fistula.
Arteriovenous fistula
When an abnormal channel forms between an artery and a vein, blood bypasses capillaries and flows directly into a vein from the artery. This form of fistula may be congenital or acquired after birth. Congenital arteriovenous fistulas are rare, but the acquired form may be caused by injury to a vein and artery lying side by side. Usually, the injury is caused by a piercing wound such as that from a bullet or knife attack.
For kidney dialysis, it is necessary to pierce a vein for each episode of treatment and over time, a vein can become inflamed and blood may clot. As this can cause scarring and damage to the vein, doctors sometimes deliberately create an arteriovenous fistula in order to widen the vein so that needle insertion is easier and blood flow faster. This faster blood flow makes clotting less likely.
Congenital arteriovenous fistulas that are small in size can be eliminated relatively easily using laser therapy, although fistulas that form near the brain, eye or other important body parts can be difficult to treat. Acquired forms are surgically treated as soon as possible after diagnosis. Prior to surgery, a radiopaque dye that can be detected on X-ray may be injected to highlight the fistula (a process referred to as angiography).
Further Reading