Anorectal Abscess and Fistula

Fig. 6.1
Abscess classification

  • Ischioanal: Abscesses located in ischioanal fat are bordered by the sphincter muscles medially by the levator ani in the cranial aspect, and by the ischial bone laterally. They can occur on one or both sides. Depending on the location, sometimes these can be differentiated into superficial and deep.

  • Intersphincteric: Acute abscesses located between the internal and external sphincter are very painful and not easy to detect. Chronic cavities often remain as incomplete internal fistulas. Since they usually drain through the tracts of the infected anal glands, pus may be suddenly purged during examination; others perforate distally. Also, these abscesses can rise to the supralevator level and lead to suprasphincteric fistulas.

  • Subanodermal/submucosal: This kind of abscess is located superficially between the sphincter and the anoderm (subanodermal) or rectal mucosa (submucosal). For this reason we distinguish between subanodermal and submucosal abscesses. These terms are also often used as synonyms.

  • Supralevatoric: This abscess is located in the retroperitoneal fat outside the rectal wall and above the levator muscle. Another synonym for abscesses of this kind is retrorectal abscess. These often extend on both sides and are therefore called “horseshoe” abscesses.

Anal fistulas are classified using the same system as abscesses: according to their anatomic relation to the anal sphincter (Fig. 6.2). In nearly all (except extrasphincteric fistulas) the origin is cryptoglandular and therefore the internal opening lies at the dentate line.


Fig. 6.2
Fistula classification

  • Submucosal (synonym: subanodermal): run under the anoderm or the rectal mucosa

  • Intersphincteric: cross the internal sphincter and reach the skin, mostly near the anus

  • Transsphincteric: cross the internal and external sphincters, protrude from the ischioanal fossa, and reach the external skin, mostly a few centimeters from the anus. we should distinguish A distal (low) or proximal (high) position should be distinguished, depending on their height. Some authors describe the location of a fistula depending on the affected third of the anal sphincter.

  • Suprasphincteric: cross the internal sphincter, run proximally in the intersphincteric plane, curve around the complete external sphincter, and reach the skin.

  • Extrasphincteric: originate in the distal rectum, pass through the rectrorectal space and the pelvic floor from a proximal direction, protrude from the ischioanal fossa, and reach the skin

There is a distinction between primary and recurrent fistulas, and between straight and curved tracts. Surgeons often differentiate into simple and complex fistulas (e.g., a complex fistula occurs when more than one-third of the sphincter is affected). Two special forms are anorectovaginal fistulas and horseshoe fistulas [25].

6.4 Symptoms

In most cases patients experience intense, somewhat pulsating pain, sometimes with fever and a distinct sensation of being ill. Here also the pathology is dependent on the exact location of the abscess. This typical presentation is mostly seen with distal (perianal, low intersphincteric, transsphincteric) locations. If the abscess develps in a proximal direction (high intersphincteric, pelvirectal, supralevatoric), the symptoms are not distinct at first. Pain will decline considerably in the case of spontaneous perforation, but it does not resolve completely. Such perforation can occur toward the outside, into the anal canal, or into the rectum, depending on the initial location. After perforation, spontaneous drainage can cause persistent drainage or might heal at the dermal surface, which causes retention of fluids and thereby a recurrence of symptoms. After the spontaneous perforation of (or a deficient operative incision into) an abscess, an anorectal fistula may remain or develop. Complete healing without a persisting fistula in up to 40 % of cases is described by some authors, but no convincing figures are available. Fistula healing without complications can only be expected when the abscess is opened operatively and the corresponding fistula is removed completely.

Contrary to abscesses, the clinical pathology of perianal fistulas is characterized by chronic complaints and discomfort. Secretion predominates; its intensity varies and is often accompanied by anal eczemas. If the external fistula opening will be epithelialized,“sham healing” sometimes occurs. In this case the external opening is temporarily closed with a thin layer of epithelium, but the fistula itself does not heal completely. Then it is only a matter of time until the fistula reopens, with secretion occurring again. In the case of anorectal fistulas, spontaneous remission rarely occurs; in general, healing cannot be expected. Recurrent and variably strong secretion is the expression of a chronic inflammatory infiltrate. Without treatment this can lead to an extension of the disease, with the potential to develop new abscesses and more fistulas. In the long run this leads to impairment and disorders of continence. In the case of immunological dysfunctions, phlegmons with septic and therefore life-threatening conditions can occur. Also, fistula carcinomas have been described over the course of many years with long-lasting diseases [6].

6.5 Diagnostics

It is easy to diagnose an acute abscess through its typical history, clinical pathology, and symptoms and using inspection and palpation. Ischioanal abscesses, when located superficially, mostly show a reddish livid discoloration with an explicitly visible prominence. Extended abscesses can lead to a dislocation of the rima ani and occasionally show fluctuation at palpation. Initially it can be difficult to reliably objectify a pelvirectal or deep ischiorectal abscess. A bidigital rectal examination, with palpable swelling and pain at pressure/touch, is a help in such cases. Only in selected cases are high-tech diagnostic methods necessary (e.g., transanal endosonography, transcutaneous sonography, or pelvic floor magnetic resonance imaging [MRI]; Figs. 6.3 and 6.4).


Fig. 6.3
Right anterior ischioanal abscess (11 o’clock in the lithotomy position)


Fig. 6.4
Retrorectal, supralevatoric, horseshoe abscess

Most fistulas are easy to diagnose: you see the external opening, you feel the internal opening, and you can find the tract by probing. During digital examination, the course of a fistula often can be palpated as a stringlike structure. Only with a complicated courses might there be difficulties in diagnosing an anorectal fistula. The external opening of an anal fistula is usually easily perceptible, but locating the internal opening may be difficult sometimes. In the case of cryptoglandular fistulas, the internal opening is generally found at the dentate line. The clinical experience of the therapist is crucial in the diagnostic investigation of anal fistulas. While dorsal anal fistulas take a curved course, ventral fistulas generally proceed straight (Goodsall’s rule). According to this, fistulas with an external opening dorsal to a line between 3 and 9 o’clock in the lithotomy position (the “anal horizon”) run predominantly curved, and those with an opening ventral to this line are straight (there are, of course, exceptions to this old rule). In the case of restrained inflammation, the fistula’s course can be followed easily with a small metal probeWith pronounced inflammation, however, probing can be problematic; there might be a danger of causing a via falsa, which often leads to complicated fistulas. This ought to be considered, especially in the case of fistula courses with secondary tracts. Thus, probing should never be mandated and whenever possible should be done by an experienced physician.

The clinical examination may be performed under anesthesia since the probing of fistulas is painful and often fails. Operations are almost always necessary, and thus can be performed while the patient is still anesthetized.

As a primary instrumental examination, anal endosonography is simple, inexpensive, and immediately available. Endosonography or MRI should be considered but are only necessary for complex or recurrent fistulas. Both of these largely depend on the examiner but are otherwise comparable; endosonography is considerably cheaper and can be conducted intraoperatively. In the case of complex fistulas that have larger cavities and run far away from the midline, MRI of the pelvic floor and the small pelvis might be indicated and superior to ultrasound (Fig. 6.5). A radiographic examination of fistulas (fistulography) is now obsolete because it just shows the fistula and does not sufficiently visualize its three-dimensional course.


Fig. 6.5
Chronic fistulas on both sides in a patient with Crohn’s disease

6.6 Differential Diagnosis

Differential diagnosis of a dorsal sinus pilonidalis in the rima ani usually is not difficult. Perianal acne inversa (synonym: hidradentitis suppurativa) may be a problem in the differential diagnosis, especially with regard to the differentiation of perianal Crohn’s disease. The most frequent differential diagnosis is a fistula caused by Crohn’s disease (this is strictly defined; it is not really a differential but an additional diagnosis). Perianal fistulas caused by tuberculosis are rare (1–3 %) in Europe, but in India, for example, this is the most common cause of fistulas.

Without any therapy, fistula in ano can lead to an expansion of inflammation with the potential to develop new abscesses and fistulas. This primarily results in permanent impairment and disorders of anal continence. In the case of long-lasting chronic inflammation, fistular carcinomas are reported in singular cases; on the whole these are extremely rare.

6.7 Abscess Treatment

Surgical interventions are the first-line treatment for anorectal abscesses [68]. An anorectal abscess is an emergent indication for surgery because of the dangers of progression into the surrounding structures and –rarely – life-threatening systemic sepsis. Therefore, incision and adequate drainage should follow directly after diagnosis. Unsuitable measures, such as waiting until fluctuation occurs, providing a therapy with any ointment, or administering only antibiotics, can cause a delay. A supplementary therapy with antibiotics should be exceptional (e.g., diffuse pararectal extension, immunosupression, or septic systemic reactions). The insertion of only a draining catheter is indicated in a few special cases but is insufficient even for an uncomplicated abscess.

During operations to repair anorectal abscesses, the surgeon should simultaneously search for the cause. If they find a connection to the anal canal or distal rectum, they should either primarily dissect it or initially place a drainage seton to provide a later final therapy. Rough manipulation should be avoided because of the danger of a causing a via falsa.

  • Perianal excision: Smaller perianal abscesses can often be incised and drained in the outpatient department as an initial measure; however, sufficient drainage and complete unroofing, respectively, must be achieved; subsequently the wound heals with secondary intention (Fig. 6.6a–d).


    Fig. 6.6
    (ad) Treatment of an acute anal abscess with wide drainage

  • Drainage into the anal canal: An intersphinctary abscess is often diagnosed too late because the typical redness and swelling in the perianal region are missed. Many times it can only be recognized by acute, fierce, regional pain in the anal canal. When in doubt, an examination while the patient is anesthetized and subsequent complete unroofing of the abscess – in most cases dissecting the distal parts of the internal sphincter – are recommended. If the abscess is in the upper part of the anal canal, internal drainage into the anal canal is indicated. When an intersphincteric abscess extends toward the retrorectal region, the drainage must be directed into the distal rectum. Here a wide excision of the rectal wall is often inevitable. This should be carried out in a way that leaves no cavities with insufficient drainage; also, a partial dissection – in this case of a proximal part of the internal sphincter – might be necessary.

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Oct 30, 2017 | Posted by in ABDOMINAL MEDICINE | Comments Off on Anorectal Abscess and Fistula

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