A fistula (plural, fistulae or fistulas) is an abnormal connection between two linings, or epithelial layers, of the body such as the mouth, lungs, bladder, bowel and skin. To the lay person, a fistula can sound pretty scary or disgusting - a connection between two parts of their body that isn't meant to be there, allowing substances such as stools¹ to move from one part to another and cause all sorts of problems.

Epithelial Surfaces

Epithelial surfaces appear in quite a few places, lining as they do such things as the skin, the nose, the mouth, the trachea/windpipe, the lungs, the bowels (gullet/oesophagus, stomach, small bowel, colon, rectum and anus), the bladder, the vagina, the bile ducts, and so on. Anatomically, quite a few of these structures lie near to each other, and since any two surfaces that lie near each other can form a fistula, there are many possibilities:

• Between the mouth and the nose - an oronasal fistula
• Between the mouth and the antrum of the maxillary sinus² - an oroantral fistula
• Between the small bowel and the skin - an enterocutaneous fistula
• Between the large bowel and the bladder - a colovesical fistula
• Between the rectum and the vagina - a rectovaginal fistula
• Between the rectum or anus and the skin surrounding the anus - a fistula-in-ano
• Between an artery and a vein - an arteriovenous fistula
• Between the windpipe and the gullet - a tracheoesophageal fistula

The list is by no means limited to the above, but in general, it is the obstetric fistulae (see also the section on obstetric fistulae, below) and fistulae-in-ano that are referred to as fistulae by the general public. A fistula should not be confused with a sinus, which is a blind hole leading from one organ without passing into another, or an abscess, which is a pus-filled cavity inside the body.

Causes

A fistula can form for a number of reasons, with the most common being:

• Crohn's disease - fistulae are a common feature of this inflammatory bowel disease, which can affect any part of the gut from the mouth to the anus. It can thus lead to fistulae between separate loops of the small bowel as well as between the gut and other parts of the body, such as the skin.

• Diverticular disease - diverticulae are outpouchings of the large bowel. They are ideal candidates for fistulae as they can end up perforating via abscesses in their walls, thus allowing formation of fistulae into other parts of the bowel or other organs.

• Malignancy - cancer of the bowel or another part of the body can also perforate and produce a fistula.

• Trauma - severe damage to the body can understandably create a hole between two places, which then heals over as a fistula.

• Radiation - damage to normal tissues due to radiotherapy can lead to an opening between two surfaces.

• Gallstones - the presence of a stone in the gallbladder or bile ducts can lead to the creation of a fistula.

• Sepsis - infection can lead to abscess formation, which in turn can lead to fistula formation if the abscess forms between two surfaces and then bursts.

Classification

A fistula can be easily classified according to the surfaces involved, its level of output, and whether it is a simple or complex fistula. Anatomical location can usually be described by combining the names for the two surfaces that the fistula connects - for example, 'gastrocolic' for a fistula between the stomach and the colon.

Output can be defined according to the volume of fluids and solids that pass through the fistula - high output is anything above 500ml per day. Finally, a simple fistula is a straightforward connection from one surface to another, whereas a complex fistula can involve an abscess or may consist of several tracts (branches).

Problems with Fistulae

Due to their nature, fistulae can cause leaking of food, bile, lymph fluid, oxygenated blood³ and so forth away from where it is needed, and can lead to leakage of bacteria-laden stools into what are normally sterile parts of the body. Fistulae can therefore lead to malnutrition due to food leaking out of the bowel, infection due to stools leaking into sterile organs, nausea and vomiting if stools leak backwards into the upper part of the gut, and unpleasant leakage of flatus and faeces into places where it is not wanted.

Obstetric Fistulae

Obstetric fistulae, vesicovaginal⁴ and rectovaginal⁵ fistulae which occur when difficult childbirth takes place without medical attention, present a humiliating and traumatising problem for mothers in the Third World where such problems are not routinely treated. The damage caused by childbirth leaves the mother incontinent⁶, with the contents of her bowels and/or bladder leaking out through her vagina. This condition can lead to ulceration of the damaged area, damage to nearby nerves, and damage to the kidneys as infection of the bladder tracks upstream. The problem currently affects around two million women in poorer countries, but is both preventable and surgically repairable and is thus the subject of a campaign by the United Nations Population Fund.

Fistulae-in-ano

Fistulae-in-ano form between the rectum or anus and the skin around the anus, and thus cause a degree of faecal incontinence as faeces pass out of the rectum, bypassing the mechanisms that usually keep it in. Fistulae-in-ano usually present as small skin bumps which enlarge and become painful until they burst, revealing faeces-filled abscesses which will then seal off again and repeat the process.

Management of Fistulae

Fistulae can be managed by doctors using the following algorithm, which is represented by the word 'SNAPS':

• Sepsis - it should be determined whether the fistula is infected or is causing infection of some part of the body. Antibiotics are usually given if an infection is present, and pus-filled abscesses are drained.

• Nutrition - next, the patient should be checked for malnutrition due to leaking of food out of the bowels, and extra nutrition (either by mouth, through a nasogastric tube⁷, or via an intravenous drip) is given if necessary.

• Anatomy - the fistula is examined and investigated using scans to determine its course and whether it has multiple tracts.

• Procedure - a surgical procedure can be performed in an attempt to fix the problem, although some fistulae can be manageable without operation or may spontaneously heal in the long term. Some fistulae are repaired by separating the surfaces and closing the holes of the fistula, while fistulae-in-ano can also be treated by passing a thread known as a seton through the fistula and tying it off. This keeps the fistula open, thus preventing the cycle of abscesses filling and bursting through the skin and, if a cutting seton is inserted, also encourages the body to slowly heal off and expel the fistula. However, cutting setons can cause damage to the sphincters, and so more conservative treatments such as the injection of fibrin glue into a fistula-in-ano are also used, although these techniques may only provide a temporary cure as opposed to a definitive one.

• Surveillance - patients with fistulae are followed up to ensure that their fistulae are properly managed, or to check for recurrence.