ANORECTAL FISTULA �

Issah J. kiswagala

(M.B.B.S)

DEFINITION

• An anorectal fistula (Fistula-in-Ano) is an abnormal channel that leads from the anus or rectum usually to the skin near the anus but occasionally to another organ, such as the vagina.

OR

• An anorectal fistula is the chronic manifestation of the acute perirectal process that forms an anal abscess.
• It usually occurs in a pre-existing anorectal abscess which burst spontaneously

SURGICAL ANATOMY

• The anus is the opening at the end of the digestive tract where stool leaves the body.
• The rectum is the section of the digestive tract above the anus where stool is held before it passes out of the body through the anus.
• The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine.
• The rectal lining consists of glistening red tissue containing mucus glands much like the rest of the intestinal lining. The lining of the rectum is relatively insensitive to pain, but the nerves from the anus and nearby external skin are very sensitive to pain.

• The external sphincter muscle is a striated muscle under voluntary control by three components: submucosal, superficial, and deep muscle. Its deep segment is continuous with the puborectalis and forms the anorectal ring, which is palpable upon digital examination.
• The internal sphincter muscle is a smooth muscle under autonomic control and is an extension of the circular muscle of the rectum.
• Typically, there are eight to 10 anal crypt glands at the level of the dentate line in the anal canal, arranged circumferentially.
• These glands penetrate the internal sphincter and end in the intersphincteric plane. They provide a path by which infecting organisms can reach the intramuscular spaces.

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Anatomy of anal glands (Cryptoglands of Morgagni).

EPIDEMIOLOGY

• The true prevalence of fistula-in-ano is unknown.
• The incidence of a fistula-in-ano developing from an anal abscess ranges from 26% to 38%.
• The male-to-female ratio is 1.8:1.
• The mean patient age is 38.3 years.

AETIOPATHOGENESIS

• The cryptoglandular hypothesis states that an infection begins in the anal canal glands and progresses into the muscular wall of the anal sphincters to cause an anorectal abscess.
• After surgical or spontaneous drainage in the perianal skin, a granulation tissue–lined tract is occasionally left behind, causing recurrent symptoms. Multiple series have shown that formation of a fistula tract after anorectal abscess occurs in 7-40% of cases.
• Other fistulas develop secondary to trauma (e.g. rectal foreign bodies), Crohn disease, anal fissures, carcinoma, radiation therapy, actinomycoses, tuberculosis, and lymphogranuloma venereum secondary to chlamydial infection.
• In the vast majority of cases, fistula-in-ano is caused by a previous anorectal abscess.

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CAUSES

• The cause of Anorectal fistula (fistula-in-ano) can be;
• Cryptoglandular—90%.
• Non-cryptoglandular (other causes)—10%.

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CRYPTOGLANDULAR CAUSE

• It is the infection of the intersphincteric glands that initiates the fistula-in-ano, known as the “cryptoglandular hypothesis”
• These glands present in the subepithelium and internal sphincter
• These glands secrete mucus to lubricate anus
• Infection in the intersphincteric gland result in formation of abscess and later fistula.

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ANAL GLANDS

NON-CRYPTOGLANDULAR CAUSE

• The following are the other cause of anorectal fistula;
• Tuberculosis
• Carcinoma; Colloid carcinoma of rectum can present as multiple fistulae-in-ano.
• Crohn’s disease, Ulcerative colitis, actinomycoses
• lymphogranuloma venereum secondary to chlamydial infection.
• Hidradenitis suppurativa (severe, chronic and recurrent pus-producing infection of apocrine sweat glands)
• Trauma e.g. rectal foreign bodies
• Anal fissures
• Radiation therapy

CLASSIFICATION OF FISTULA

• Fistula-in-ano can be classified according to;
• Standard (Milligan Morgan, 1934; Goligher 1975) classification
• Park`s classification (1976)

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STANDARD (MILLIGAN MORGAN, 1934; GOLIGHER 1975) OF FISTULA-IN-ANO CLASSIFICATION

• Fistula-in-ano is classified as
• Subcutaneous
• Submucous
• Low anal
• High anal
• Pelvi-rectal

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PARK`S CLASSIFICATION

• Is the one most commonly used
• There are four types of Parks classification
• Type 1: Intersphincteric:
• Type 2: Transsphincteric
• Type 3: Suprasphincteric
• Type 4: Extrasphincteric

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Type 1: Intersphincteric

• The fistula is confined to the intersphincteric plane.
• Common course - It begins at the dentate line, then tracks via the internal sphincter to the intersphincteric space between the internal and external anal sphincters, and finally terminates in the perianal skin or perineum
• It is the commonest fistula accounting 70%
• It is the result of a perianal abscess
• Other possible tracts - No perineal opening; high blind tract; high tract to lower rectum or pelvis

Type 2: Trans-sphincteric

• The fistula traverses the external sphincter, communicating with the ischiorectal fossa.
• It accounts for 25% of fistula-in-ano.
• Common course - It tracks from the internal opening at the dentate line via the internal and external anal sphincters into the ischiorectal fossa and then terminates in the perianal skin or perineum
• Results from an ischiorectal fossa
• Other possible tracts - High tract with perineal opening; high blind tract abscess

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Type 3: Suprasphincteric:

• The fistula extends cephalad over the external sphincter and perforates the levator ani.
• It accounts for 5% of fistula-in-ano.
• Common course - It passes from the internal opening at the dentate line to the intersphincteric space, tracks superiorly to above the puborectalis, and then curves downward lateral to the external anal sphincter into the ischiorectal fossa and finally to the perianal skin or perineum
• It arises from a supralevator abscess
• Other possible tracts - High blind tract (ie, palpable through rectal wall above dentate line)

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Type 4: Extrasphincteric:

• The fistula extends from the rectum to the perianal skin, external to the sphincter apparatus.
• It accounts for 1% of fistula-in-ano.
• Common course - It runs from the perianal skin via the ischiorectal fossa, tracking upward and through the levator ani muscles to the rectal wall, completely outside the sphincter mechanism, with or without a connection to the dentate line
• It may arise from foreign body penetration of the rectum with drainage through the levators, from penetrating injury to the perineum, from Crohn disease or carcinoma or its treatment, or from pelvic inflammatory disease

CLINICAL FEATURES

• Patients often provide a reliable history of previous pain, swelling, and spontaneous or planned surgical drainage of an anorectal abscess. Signs and symptoms of fistula-in-ano, in order of prevalence, include the following:
• Perianal discharge presents with seropurulent discharge (65%)
• Pain
• Skin excoriation with skin irritation
• One or more external opening may be present with induration of the surrounding skin.
• Swelling, Bleeding or Diarrhea
• Often it may heal superficially but pus may collect beneath forming an abscess which again discharges through same or new opening.

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• Important points in the patient’s history that may suggest a complex fistula include the following:
• Inflammatory bowel disease
• Diverticulitis
• Previous radiation therapy for prostate or rectal cancer
• Tuberculosis
• Steroid therapy
• HIV infection

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THE GOODSALL RULE

• In simple cases, the Goodsall rule can help anticipate the anatomy of a fistula-in-ano.
• This rule states that fistulas with an external opening anterior to a plane passing transversely through the center of the anus will follow a straight radial course to the dentate line.
• Fistulas with their openings posterior to this line will follow a curved course to the posterior midline.
• Exceptions to this rule are external openings lying more than 3 cm from the anal verge. These almost always originate as a primary or secondary tract from the posterior midline, consistent with a previous horseshoe abscess.

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• A fistula, with an external opening in the anterior half of anus within 3 cm tends to be direct type and in the posterior half, indirect type or curved and sometimes horseshoe type.

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Figure shows anterior fistula-in-ano (single)

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Figure shows fistula-in-ano both anterior and posterior (Multiple).

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PHYSICAL EXAMINATION

• Observe the entire perineum, looking for an external opening that appears as an open sinus or elevation of granulation tissue.
• Spontaneous discharge of pus or blood via the external opening may be apparent or expressible on digital rectal examination.
• Digital rectal examination (DRE): Lateral or posterior induration suggests deep postanal or ischiorectal extension

DIFFERENTIAL DIAGNOSES

• The following are differential diagnosis of fistula-in-ano;
• Urethral fistula in male
• Chronically infected Bartholin gland abscess in females
• Pilonidal sinus disease
• Hidradenitis suppurativa
• Infected inclusion cysts
• Crohn’s tuberculosis, ulcerative colitis
• Carcinoma

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INVESTIGATIONS

• The following are investigation that may be ordered;
• Full blood picture
• Pus for ZN-stain, methylene blue dye study
• Swab for culture and sensitivity.
• barium enema X‑ray.
• If required fistulography under anaesthesia can be done (involves injection of contrast via the internal opening, which is followed by anteroposterior, lateral, and oblique radiographic images to outline the course of the fistula tract).
• Endoanal or endorectal ultrasonography, Colonoscopy
• Chest X-ray, MRI, CT scan

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TREATMENT

• Adequate and appropriate treatment is dependent on correct classification of the fistula and identification of the internal and external openings, the course of the track, and the amount of sphincter muscle involved.
• Treat the underlying cause to prevent recurrence.
• Surgical treatment remains the primary modality of treatment for noninflammatory bowel disease–related fistulas.
• Refer the patient to a center with expert
• Requires staged procedure - initial colostomy is done followed by definitive procedure. This prevents sepsis and promotes faster healing.
• Later closure of colostomy is done.

• Surgical options for fistula-in-ano
• Fistulectomy
• Fistulotomy
• Advancement flaps
• Gluing of the fistula
• Anal fistula plug (AFP) repair:
• VAAFT procedure (Video assisted anal fistula track ligation)
• LIFT technique (Ligation of intersphincteric fistula track)
• Fistula clip closure
• Seton Technique

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COMPLICATIONS

Early postoperative complications

May include the following:

• Urinary retention
• Bleeding
• Fecal impaction
• Thrombosed hemorrhoids

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Delayed postoperative complications

May include the following:

• Recurrence
• Incontinence (stool)
• Anal stenosis - The healing process causes fibrosis of the anal canal; bulking agents for stool help to prevent narrowing
• Delayed wound healing - Complete healing occurs by 12 weeks unless an underlying disease process is present (i.e. recurrence, Crohn disease)

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Complications are usually the result of fistula surgery