Anal Fistulas

Definition

Anal fistulas are small pathological and infected tunnels that connect the anus with the surrounding skin. Specifically, to be defined as such, anal fistulas must develop in the precise anatomical site - called "combed line or anorectal line" - which separates the rectum from the anus, in which the exocrine anal glands are housed.

To understand: what are anal glands?

The anal glands - called precisely Hermann's glands and Desfosses in memory of their discoverers - are tiny anatomical structures located along the wall of the anal canal. Their tubular glandular conduits secrete their own contents in the anal crypts (small depressions in the shape of a swallow's nest that are arranged in the anal region in a curiously circular way).

Anal fistulas are the final outcome of an infection of these glands which, progressing, degenerates into abscess.

• In other words, anal fistulas represent the immediate complication of an inadequately treated anal abscess.

How they are formed

We have seen that anal fistulas represent the direct consequence of an untreated abscess (infection).

To develop the fistula, the infection must originate at the level of the crypt: the pathogens manage to penetrate the sphincteric apparatus reaching the crypts of the anal glands.

When the anal glands become inflamed (for example due to a passage of pathogens from the faeces) a pus sac is formed which, breaking, gives rise to the anal fistula.

But the process that leads to the formation of the fistula can also be different: in certain circumstances, in the anal crypts, fecal residues or mucous secretions are blocked, such as to favor the infection of the glands. In turn, the infectious process can be induced either by the entry of fecal material into the excretory tubules, or by a blockage in the outflow of the glands.

Remember that ...

Anal abscess and anal fistula represent two evolutionary stages of the same disease: in fact, the abscess is the acute complication of an infection, while the anal fistula is its chronic form.

• There is no anal fistula without abscess

Causes and risk factors

Fistulas can be favored by various factors, the same responsible for anal abscesses:

• Anal ulcers
• Inflammatory bowel diseases, such as Crohn's disease, diverticulitis and ulcerative colitis. It is estimated that 50% of patients with Crohn's disease exhibit an anal fistula at least once.
• Impaired immune system: 30% of HIV patients develop anal fistulas
• Rectal cancer
• Tuberculosis
• Sexually transmitted diseases (eg chlamydia and syphilis)
• Complication of bowel surgery

Compared to women, man appears to be more sensitive to anal fistulas. Furthermore, medical statistics show that this disorder occurs with greater incidence in the young-adult male aged between 20 and 40 years.

Types of anal fistulas

Anal fistulas are not all the same: they are in fact classified essentially on the basis of structure and location.

Depending on the structure, they include:

1. Straight fistulas: they have a single communication channel
2. Fistulas with branches: more connection channels are observed
3. Horseshoe fistulas: they connect the anal sphincter to the surrounding skin, passing first through the rectum

On the basis of the location of the fistulous canaliculus, "high" fistulas can be distinguished, placed above the dentate line, and "low" fistulas, placed below. More specifically, anal fistulas can be classified in various ways, but generally reference is made to the Parks classification or to that proposed by the American Gastroenterological Association (AGA).

* A little anatomy to understand ...

The external anal sphincter is a striated muscle consisting of two bundles:

1. Subcutaneous bundle *, crossed by fibers of the complex longitudinal frock
2. Deep bundle *, the thickest part of the sphincter that surrounds the mucous membrane of the anal canal and the internal sphincter

The elevator of the anus * is instead a thin and elongated muscle, divided into three sections: pubococcygeal, puborectal and ileococcygeal

1. Superficial fistulas: localized distally (below) both to the internal anal sphincter and to the external sphincter complex (as shown in the figure do not cross the internal or external sphincter)
2. Intersfinteral fistulas: localized between the internal anal sphincter and the external sphincter complex; they can extend down to the perianal skin, upwards (blind) or open up into the rectum
3. Transphincteric fistulas: they cross the intersphincteric space and the external anal sphincter; they therefore pass through both the internal and external sphincters
4. Supraphosphoric fistulas: they pass through the internal sphincter, pass upwards around the external sphincter above the puborectal muscle, then move downwards, penetrating the levator muscle before heading towards the skin
5. Extrasfinteriche fistulas: they have a route that starts above the internal anal sphincter and ends in the external cutaneous orifice.

Signs and symptoms

To learn more: Anal Fistula Symptoms

The clinical picture of a patient with anal fistulas includes a tangle of rather obvious signs and symptoms.

If, in the early stages of the pathology, the patient does not realize the infection, in the acute phase the symptoms certainly do not pass unnoticed. In fact, anal fistulas cause an unpleasant sensation of irritation, itching and swelling at the anal level, which tends to become accentuated during defecation and is typically accompanied by minimal but continuous leaks of feces, pus or mucus, which keep the anal region moist causing dermatitis and itching. Perceived pain can become unbearable by performing certain movements, so that some patients struggle even to sit on a hard floor.

It is not uncommon to observe leaks of blood or pus with faeces; very often, the loss of serous material or pus from the anal orifice also occurs independently of evacuation (fecal incontinence). In some patients suffering from anal fistula, there is also a more or less significant rise in body temperature (fever / low grade).

In the absence of a pharmacological or surgical intervention, the typical symptoms of anal fistula can degenerate: the chronic inflammation given by the anal abscess can, over time, predispose to the development of malignant neoplasms.

In severely immunocompromised patients such as those affected by AIDS, the anal fistula tends to degenerate into Fournier's necrotizing fasciitis, thus extending towards the genitals and groin.

Diagnosis

The proctological examination is essential to ascertain a suspicion of anal fistula. After analyzing the symptoms reported by the patient, the doctor proceeds with the physical examination, which can also be performed after local anesthesia.

Although the verification of an anal fistula is rather simple, unfortunately the precise identification of the fistulous path is rather complex; so much so that very often the entire fistulous path can be identified only during surgery.

In general, the diagnosis consists of a delicate intraanal ultrasound (performed with a special rotating probe able to identify as much as possible the path of the canal). Here, the doctor will evaluate:

• Local redness and swelling
• Possible blood loss
• Pus leakage during rectal exploration
• Any surgical scars

When anal fistulas are very complex and branched, it is often necessary to resort to perianal magnetic resonance.

Treatment

The medical treatment of perineal fistulas includes antibiotics, immunosuppressants and immunomodulants. In general, the therapeutic efficacy of these drugs is rather low, given the high frequency of relapses at drug withdrawal. Systemic immunomodulatory therapy (see: Remicade) or local anti-TNFα therapy, on the other hand, seems to induce a rapid and stable healing of fistulas that complicate Crohn's disease, in a good percentage of patients.

The scarce tendency to definitive regression, be it spontaneous or induced by drugs, of anal fistulas pushes the doctor to subject the patient to a delicate surgery intervention. The surgical removal strategies of the fistula are numerous and varied: it will therefore be the duty of the physician to determine how to act, based on the structure and length of the fistula. The ultimate goal of these interventions is the permanent eradication of the suppurative process without compromising the patient's anal continence

Deepening: main types of intervention

Invasive interventions

1. Fistulotomy : it is typically reserved for patients with simple fistulas; this intervention consists in the literal flattening of the canaliculus. The procedure is not burdened with a significant risk of incontinence.
2. Fistulectomy : involves the dissection of the entire fistula and a micro portion of the surrounding healthy tissue.
3. Setone : it is a sort of big wire (small tube) inserted through the fistula and subsequently joined to its two ends outside the body. The seton has two potential advantages: the first is the continuous drainage of the material contained in the fistulous tunnel (such as pus), which comes out outside preventing the development of complications and making subsequent surgical operations easier; the second advantage concerns the possibility of periodically putting in traction the elastic to slowly dissect the muscle tissue (ELASTODIERESI or SLOW SECTION), engraving a new segment as the previous lesion heals; doing so, clear cuts are avoided and the risk of incontinence is reduced.
4. Fistulectomy in two stages . As the term suggests, this operation is performed in two different times in order to minimize the risk of complications, such as damage to the anal sphincter and fecal incontinence. It is indicated in the treatment of complex fistulas, transfinteric and suprasfinteric, which also involve the anal muscles. In the first phase it involves the positioning of a seton which is periodically put into traction to slowly dissect the muscle tissue (ELASTODIERESI or SLOW SECTION). The treatment with setone lasts a few months and is obviously not very satisfying for the patient. By tensioning the seton, the fistulous orifice is lowered more and more, allowing a fistulotomy or fistulectomy to be performed as soon as the section of the muscular plane (previously carried out through the seton) gives way to a solid scarring.
5. Endorectal flap : consists of the reconstruction of the mucosa, of the submucosa and occasionally of the circular muscle layer, obtained by applying a well vascularized flap of the rectal mucosa (taken from the overlying rectum) on the internal opening of the fistula (fistula orifice). With this procedure, the probability of incontinence is 35%.

Innovative and minimally invasive treatments that eliminate post-operative complications such as fecal incontinence (which occurs in about 10-30% of cases).

1. Closure of the fistula with fibrin glue . The intervention has a modest cure rate, in the order of 20-60%. It involves the injection of a soluble mixture inside the previously cleaned fistulous tunnel (debriding) in order to seal it, just as a glue would do. The advantages are linked to the minimally invasive intervention, which cancels many of the typical complications of traditional interventions (including incontinence) and ensures a faster return to normal activities. However, the risk of relapses remains high, with low success rate of anal healing of fistulas.
2. Closure of the fistula with medicated plugs (plug), resistant to infections and inert (they do not generate foreign body reactions). These treatments, which are less invasive than traditional surgical procedures, are performed by inserting in the fistula special "medicated anal plugs" (fistula plug) that favor the generation of new tissue, and are then reabsorbed spontaneously by the body. Also in this case the post-intervention complications are almost nil, including the risks of incontinence; the therapeutic success rate is good (40-80%) but an important risk of recurrences remains.
3. LIFT technique (ligation of inter sphincteric fistula tract): an innovative surgical procedure based on the secure closure of the internal fistulous orifice (through the intersphincteric space and not via the endorectal one) and on the concomitant removal of the infected cryptoglandular tissue (due to fistulas). It is a recent minimally invasive, safe, effective and inexpensive technique, with a good success rate and a low risk of recurrence.
4. VAAFT (Video Assisted Anal Fistula Treatment): it uses advanced diagnostic tools (operative fistuloscope) that allow first of all to have a direct view of the fistulous path from the inside, also highlighting any local complications. In addition to vision, this device allows you to clean and cure the fistula itself from its inside, following the operating steps on the monitor step by step; moreover, the operation involves the hermetic closure of the internal orifice of the fistula by transanal, important to avoid the passage of fecal material through the fistula. The technique is particularly suitable for the treatment of complex perianal fistulas. By treating the fistula from the inside, the risk of causing damage to the sphincters is eliminated; also in this case, therefore, the risk of postoperative incontinence is zeroed.

Most of the time, the patient is operated on in day hospital, which means he can go home the same day as the operation. For more complicated fistulas, however, the patient can be held in the hospital for two or more days.

Post intervention

After surgery, the perception of a slight pain must be considered an absolutely normal condition. Even blood losses represent, within certain limits, a fairly common post-intervention risk. Following an operation for an anal fistula, the pain can be controlled by administering painkillers, whose doses must always be established by the doctor.

Furthermore, to minimize pain, the patient can perform gentle warm-hot water packs (hip bath) on the intervention area. To facilitate evacuation, the doctor may prescribe laxatives or softening stool medications.

The possible intake of antibiotics (prior medical prescription) to be taken by mouth can prevent the onset of post-intervention infections.

The main risks associated with an anal fistula operation are:

1. Infections
2. Fecal incontinence
3. Relapsing fistula

The desirable approach is to avoid casuistry number 2 as much as possible; in other words, we try to safeguard sphincter continence by adopting (whenever possible) minimally invasive techniques, even if this is to the detriment of the success rate (lower) and the risk of recurrence (higher), compared to traditional surgical techniques. However, such an approach often involves higher healthcare costs, a problem that is not insignificant if we consider the current socio-economic situations in the country.

The post-intervention risks can be partly prevented by paying particular attention to wound hygiene and respecting absolute rest: in this way, the wound is prevented from being infected and the anal fistula is present again.