Classification and pathological anatomy

A review of the literature shows a wide variation in classification and nomenclature of perianal fistulae and abscesses. Therefore, in this paper the classification based on A. Parks is used. According to this, the classification of anorectal abscesses and fistulae is given by their location (figure 1).

Figure 1

a. Typical location and extent of anorectal abscess and fistula: 1 intersphincteric, 2 transsphincteric (ischiorectal), 3 extrasphincteric, 4 submucosal. b. Therapy: abscess incision and incision/excision of fistula.

Superficial infections may lead to submucosal or subcutaneous abscesses. If the abscess perforates the external sphincter, an ischiorectal abscess develops. If the intersphincteric abscess spreads cranially beyond the levator muscles, a pelvirectal abscess results. Semicircular and, mostly, posterior progression of the infection leads to a horseshoe abscess or fistula formation.

A fistula develops as the result of spontaneous perforation of the abscess, or of surgical incision. If the external and internal (anal) ostium can be verified by examination, the so called complete fistula will be treated as later shown. An incomplete fistula has only one orifice.

Symptoms

Diagnosis

Diagnostic procedures are aimed at the exact localization of the abscess or fistula in order to perform adequate surgical therapy leading to full functional recovery of the patient.

Therapy

Anal fistula

Fistulae should be classified prior to surgery, since the crucial point for the right surgical approach and functional results is the exact preoperative localization of the tract of the fistula (grade B and C). Fistulotomy of subcutaneous or submucosal fistulae can be performed with a probe. No extra excision of the fistulous tract is necessary, the wound can remain open for secondary healing. Exact localization of the inner opening of the fistula can be attained by endosonography or by probes. Alternatively, some authors describe techniques using primary closure or marsupialization of the wound edges to the fistula ground to obtain better functional results and/or earlier healing (grade B).

If less than the distal two thirds of the internal sphincter muscle are involved the respective distal sphincter parts and the anoderm can be cut as previously described for subcutaneous fistulae. Impaired continence is unlikely to develop. The wound should also remain open for secondary healing. Recent literature suggests an approach which preserves the sphincter better, because follow-up studies after surgery for fistula-in-ano often show a decreased sphincter tonus and impaired continence. This observations, combined with EUS findings of occult sphincter damage after fistulotomy with division of the internal sphincter is used as argument for sphincter-preserving procedures (as described for transsphincteric fistulae (grade B and C)).

Transsphincteric fistulae

If more than two thirds of the sphincter muscle are affected, division of the sphincter muscle without loss of continence is unlikely. Therefore, it is recommended not to severe the sphincter muscle. Even if there will be no incontinence at first, physiological aging may cause muscular weakening in the long-term (grade C).

Staged procedures are sometimes necessary. In a first step the fistula is identified and marked with a seton. This may require anesthesia (1, 7, 9). At the same time, external tracts of the fistula are laid open. If there are no inflammatory changes or if inflamed tissue can be resected, closure of the internal ostium may be achieved by single stitch sutures. More often a second intervention is necessary to excochleate the remaining outer part of the fistula, if excision is not possible. The inner ostium is excised out of the sphincter muscle, the muscle is sutured and the row of sutures is covered by a mucosal advancement flap (2, 3), which is dissected from the mucosa cephalad to the internal aperture and sutured to the lower margin of the mucosa (figure 2). Alternatively a full-thickness rectal (wall) advancement flap may be used, showing better results in certain indications (grade B and C).

Figure 2

Sliding flap. a, b. Coring out of all the fistulous tract and anal gland. c. Mobilization of a mucosal flap. d. Closure of muscular gap. e. of the mucosa.

Extrasphincteric fistulae

The cure of extrasphincteric fistulae may also include several surgical procedures. In a first step the outer part of the fistula should be excised. If the internal orifice can be securely identified, the fistula can be closed either using a mucosal or rectal advancement flap or with direct suture protected by a diverting colostomy (2, 3).

Some authors recommend the use of a cutting seton to avoid surgical division of the sphincter apparatus. The published data show good functional and satisfying results, although the therapy needs a long time (grade C).

Recto-vaginal fistulae

A particular form of fistula is the recto-vaginal fistula. Exact preoperative diagnosis is essential to determine exactly size and localization, to assess the stage of the anal sphincter, and to reveal the cause of the fistula such as Crohnís disease, radiation, obstetric injury, neoplasia, operative trauma. The surgical approach depends on the level of the opening of the fistula into the rectum and into the posterior wall of the vagina [2].

Recto-vaginal fistulae have to be differentiated from ano-vaginal fistulae which originate from the anal canal distal to the dentate line. Recto-vaginal fistulae are classified according to their location, size, and etiology. Most surgeons arbitrarily classify a fistula as low when it can be repaired from a perineal approach and as high if it can be approached only transabdominally. The size of recto-vaginal fistulae ranges from less than 0.5 cm (small) to more than 2.5 cm (large).

The timing of the operation is determined by the likelihood of spontaneous or non-operative healing of the fistula. About one half of small recto-vaginal fistulae secondary to obstetric trauma may heal spontaneously, whereas recto-vaginal fistulae due to inflammatory bowel disease and radiation therapy of neoplasia rarely will. For this reason in certain cases a conservative approach for up to six months is recommended, which should be used to improve the patientís general condition.

For high fistulae closing should be performed from an abdominal approach. After mobilizing the rectum the fistula is transsected. Alternatively a low anterior resection of the rectum may become necessary.

Recto-vaginal fistulae opening into the distal suprasphincteric part of the rectum can be treated by a mucosal or rectal advancement flap [2]. This requires a deviation enterostomy or adequate bowel preparation followed by parenteral nutrition.

After dissection of the mucosal flap the fistulous tract is carefully excised from the muscle and the posterior wall of the vagina, followed by suture closure of the muscle. These sutures will be covered by the mucosal flap. The vaginal side of the fistula remains open.

Prior to operation exact evaluation of the sphincter muscle is mandatory. To avoid bad functional outcome additional sphincteroplasty may be required [grade C].

In conclusion, surgery of perianal abscesses and fistulae show many possible variations. As shown in the literature the surgeonís knowledge about anatomy and function, experience, technical skills and patience of both patient and surgeon is needed to achieve satisfying results [grade B and C].

References

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2.

Athanasiadis S, Oladeinde I, Kuprian A, Keller B. Endorektale Verschiebelappenplastik vs. Transperinealer Verschluss bei der chirurgischen Behandlung der rektovaginalen Fisteln. Eine prospektive Langzeitstudie bei 88 Patientinnen. Chirurg. (1995);66:493–502. [PubMed: 7607012]

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Farthmann E H, Ruf G. Zur Problematik der Kontinenzerhaltung bei der Behandlung von IBD-assoziierten Analfisteln. Schweiz Rundsch Med Prax. (1997);86:1968–1070. [PubMed: 9289805]

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Poen A C, Felt-Bersma R J, Eijsbouts Q A, Cuesta M A, Meuwissen S G. Hydrogen peroxide-enhanced transanal ultrasound in the assessment of fistula-in-ano. Dis Colon Rectum. (1998);41:1147–1152. [PubMed: 9749499]

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Sailer M, Fuchs KH, Kraemer M, Thiede A (1998) Stufenkonzept zur Sanierung komplexer Analfisteln. Zbl Chir 123: 840–805; discussion 846 . [PubMed: 9746985]

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Spencer J A, Chapple K, Wilson D, Ward J, Windsor A C, Ambrose N S. Outcome after surgery for perianal fistula. Am J Roentgenol. (1998);171:403–406. [PubMed: 9694464]

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Stoker J, Fa V E, Eijkemans M J, Schouten W R, Lameris J S. Endoanal MIR of perianal fistulas: the optimal imaging planes. Eur Radiol. (1998);8:1212–1216. [PubMed: 9724441]

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