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KembaraXtra-Medicine- Anorectal Fistula
Basic Information and Definition
An anorectal fistula is an inflammatory tract that connects the anal canal to the perianal skin. It has a primary (internal) opening in the anal canal at the dentate line and a secondary (external) opening on the perianal skin. Most fistulae develop as a complication of a perianal abscess that begins with infection of an anal crypt gland; if the abscess ruptures and the tract becomes epithelialized, a chronic fistula forms.
Classification by Relationship to the Anal Sphincter Complex
Intersphincteric fistulas are the most common and travel within the intersphincteric plane to the perianal skin. Transsphincteric fistulas are frequent and pass from the internal opening through both internal and external sphincters into the ischiorectal fossa and then to the perianal skin. Suprasphincteric fistulas are uncommon; after traversing the internal sphincter, the tract courses above the puborectalis and then descends lateral to the external sphincter into the ischiorectal space, sometimes associated with a supralevator abscess if the cavity extends upward. Extrasphincteric fistulas are rare and pass from the rectum above the levators, through the levator muscles, and into the ischiorectal space and perianal skin. Submucosal fistulas originate at the dentate line from an infected crypt without involving the sphincter muscles. Horseshoe fistulas extend from one ischiorectal fossa to the other behind the rectum. (Fistulotomy is not appropriate for extrasphincteric fistulas because of the high risk of incontinence.)
Synonyms
Fistula-in-ano and anal fistula.
ICD-10-CM Codes
K60.5 (Anorectal fistula) and K60.3 (Anal fistula).
Epidemiology and Demographics
Anorectal fistulas occur across all ages, with an average age around 39 years. They are about twice as common in men as in women. They are associated with inflammatory bowel disease and constipation. In pediatrics, they are more common in infants, with boys affected more than girls.
Physical Findings and Clinical Presentation
In the acute stage, patients may have perianal swelling, pain with defecation and sitting, and fever. In the chronic stage, symptoms include persistent pain, malodorous perianal drainage or bleeding, and anal pruritus. The external opening is often tender and inflamed, typically within 2–3 cm of the anal verge, and may express purulent or serosanguineous drainage with compression. A greater distance from the anal margin increases the likelihood of a more complex fistula with upward extension. Recurrent perianal abscess strongly suggests an underlying fistula.
Goodsall Rule
The likely course of the fistula tract can often be estimated from the external opening location. If the external opening is anterior to an imaginary transverse line through the midpoint of the anus, the tract usually runs radially to the anal canal. If the opening is posterior to that line, the tract is usually curved and enters the anal canal at the posterior midline. An important exception is an anterior external opening more than 3 cm from the anus, which may still curve posteriorly and open in the posterior midline.
Etiology
The most common cause is a nonspecific infection of an anal crypt gland involving skin or intestinal flora, and fistulas are more likely when intestinal microorganisms are cultured from the initial abscess. Other infectious causes include tuberculosis, lymphogranuloma venereum, and actinomycosis. Inflammatory bowel disease (especially Crohn disease, and less commonly ulcerative colitis) is an important cause. Trauma can lead to fistulas, including after surgery (e.g., episiotomy, prostatectomy), foreign bodies, or anal intercourse. Malignancy (carcinoma, leukemia, lymphoma) and malignancy treatment (surgery, radiation) can also cause fistula formation.
Diagnosis
Diagnosis is commonly established by history and physical examination, especially in simple fistulas, supported by anoscopy and/or further evaluation when needed.
Differential Diagnosis
Anal abscess, anal ulcer or fissure, hidradenitis suppurativa, pilonidal sinus, Bartholin gland abscess or sinus, and infected perianal sebaceous cysts.
Workup
Digital rectal examination is performed to assess sphincter tone and voluntary squeeze pressure, detect an extraluminal mass, identify an indurated tract, and attempt to palpate an internal opening or pit. Gentle probing of the external opening may be performed but should be done carefully to avoid creating a false tract; about half of patients may not have a clinically detectable internal opening. Exam alone may be sufficient for many simple fistulas. Anoscopy is used to evaluate the anal canal. Proctosigmoidoscopy is recommended to exclude inflammatory or neoplastic disease. When extensive evaluation or procedures are required, studies should be done under adequate anesthesia.
Laboratory Tests
A complete blood count may be obtained. Rectal biopsy is appropriate if inflammatory bowel disease or malignancy is suspected; biopsy of the external orifice is not useful.
Imaging Studies
Transanal endosonography (EUS) can help estimate how much sphincter would be divided during fistulotomy and can detect undrained sepsis, complex anatomy, and high blind tracts. MRI is useful for identifying suprasphincteric or extrasphincteric tracts, and MRI/EUS are generally more accurate than clinical exam in mapping fistula anatomy. CT is limited because it lacks the resolution to define tract relationships to sphincters and levators. Fistulography is rarely needed now. Colonoscopy or barium enema should be considered when IBD or malignancy is suspected, when fistulas are recurrent or multiple, or in patients younger than 25 years. A small bowel series may occasionally be obtained for similar indications.
Treatment: Nonpharmacologic
Sitz baths can provide symptomatic relief and improve comfort.
Pharmacologic Therapy
Medications are rarely recommended as primary therapy. Immunomodulators such as infliximab may be used in selected cases, particularly when fistulas are related to Crohn disease.
Acute General Management
Surgery is the treatment of choice. Broad-spectrum antibiotics are used when cellulitis is present, when the patient is immunocompromised, or when valvular heart disease or prosthetic devices are present. Stool softeners or laxatives may be used to reduce straining and discomfort.
Chronic Management and Surgical Options
Definitive management is typically surgical, tailored to fistula type and complexity. The main goals are to eradicate the fistula, prevent recurrence, preserve sphincter function, and minimize healing time. Surgical and procedural options include fistulotomy, fistulectomy, seton placement (to maintain drainage while healing occurs), fibrin glue, fistula plugs, LIFT procedure (ligation of the intersphincteric fistula tract), rectal advancement flaps, and, in select complex situations, colostomy. Strategy varies by classification; superficial/intersphincteric and low transsphincteric fistulas are often candidates for fistulotomy, while higher or more complex fistulas more often require sphincter-sparing approaches such as setons, LIFT, advancement flaps, glue, or plugs. Extrasphincteric disease requires addressing any intraabdominal or pelvic source and is not managed with fistulotomy due to incontinence risk.
Disposition
Most patients are managed with outpatient surgery.
Referral
Referral to a surgeon experienced in anorectal fistula management is recommended.
Pearls and Considerations
HIV-positive and diabetic patients who develop perirectal abscesses or fistulas should be treated as true surgical emergencies. The risk of septicemia, Fournier gangrene, and other severe septic complications makes rapid evaluation and drainage imperative.
Basic Information and Definition
An anorectal fistula is an inflammatory tract that connects the anal canal to the perianal skin. It has a primary (internal) opening in the anal canal at the dentate line and a secondary (external) opening on the perianal skin. Most fistulae develop as a complication of a perianal abscess that begins with infection of an anal crypt gland; if the abscess ruptures and the tract becomes epithelialized, a chronic fistula forms.
Classification by Relationship to the Anal Sphincter Complex
Intersphincteric fistulas are the most common and travel within the intersphincteric plane to the perianal skin. Transsphincteric fistulas are frequent and pass from the internal opening through both internal and external sphincters into the ischiorectal fossa and then to the perianal skin. Suprasphincteric fistulas are uncommon; after traversing the internal sphincter, the tract courses above the puborectalis and then descends lateral to the external sphincter into the ischiorectal space, sometimes associated with a supralevator abscess if the cavity extends upward. Extrasphincteric fistulas are rare and pass from the rectum above the levators, through the levator muscles, and into the ischiorectal space and perianal skin. Submucosal fistulas originate at the dentate line from an infected crypt without involving the sphincter muscles. Horseshoe fistulas extend from one ischiorectal fossa to the other behind the rectum. (Fistulotomy is not appropriate for extrasphincteric fistulas because of the high risk of incontinence.)
Synonyms
Fistula-in-ano and anal fistula.
ICD-10-CM Codes
K60.5 (Anorectal fistula) and K60.3 (Anal fistula).
Epidemiology and Demographics
Anorectal fistulas occur across all ages, with an average age around 39 years. They are about twice as common in men as in women. They are associated with inflammatory bowel disease and constipation. In pediatrics, they are more common in infants, with boys affected more than girls.
Physical Findings and Clinical Presentation
In the acute stage, patients may have perianal swelling, pain with defecation and sitting, and fever. In the chronic stage, symptoms include persistent pain, malodorous perianal drainage or bleeding, and anal pruritus. The external opening is often tender and inflamed, typically within 2–3 cm of the anal verge, and may express purulent or serosanguineous drainage with compression. A greater distance from the anal margin increases the likelihood of a more complex fistula with upward extension. Recurrent perianal abscess strongly suggests an underlying fistula.
Goodsall Rule
The likely course of the fistula tract can often be estimated from the external opening location. If the external opening is anterior to an imaginary transverse line through the midpoint of the anus, the tract usually runs radially to the anal canal. If the opening is posterior to that line, the tract is usually curved and enters the anal canal at the posterior midline. An important exception is an anterior external opening more than 3 cm from the anus, which may still curve posteriorly and open in the posterior midline.
Etiology
The most common cause is a nonspecific infection of an anal crypt gland involving skin or intestinal flora, and fistulas are more likely when intestinal microorganisms are cultured from the initial abscess. Other infectious causes include tuberculosis, lymphogranuloma venereum, and actinomycosis. Inflammatory bowel disease (especially Crohn disease, and less commonly ulcerative colitis) is an important cause. Trauma can lead to fistulas, including after surgery (e.g., episiotomy, prostatectomy), foreign bodies, or anal intercourse. Malignancy (carcinoma, leukemia, lymphoma) and malignancy treatment (surgery, radiation) can also cause fistula formation.
Diagnosis
Diagnosis is commonly established by history and physical examination, especially in simple fistulas, supported by anoscopy and/or further evaluation when needed.
Differential Diagnosis
Anal abscess, anal ulcer or fissure, hidradenitis suppurativa, pilonidal sinus, Bartholin gland abscess or sinus, and infected perianal sebaceous cysts.
Workup
Digital rectal examination is performed to assess sphincter tone and voluntary squeeze pressure, detect an extraluminal mass, identify an indurated tract, and attempt to palpate an internal opening or pit. Gentle probing of the external opening may be performed but should be done carefully to avoid creating a false tract; about half of patients may not have a clinically detectable internal opening. Exam alone may be sufficient for many simple fistulas. Anoscopy is used to evaluate the anal canal. Proctosigmoidoscopy is recommended to exclude inflammatory or neoplastic disease. When extensive evaluation or procedures are required, studies should be done under adequate anesthesia.
Laboratory Tests
A complete blood count may be obtained. Rectal biopsy is appropriate if inflammatory bowel disease or malignancy is suspected; biopsy of the external orifice is not useful.
Imaging Studies
Transanal endosonography (EUS) can help estimate how much sphincter would be divided during fistulotomy and can detect undrained sepsis, complex anatomy, and high blind tracts. MRI is useful for identifying suprasphincteric or extrasphincteric tracts, and MRI/EUS are generally more accurate than clinical exam in mapping fistula anatomy. CT is limited because it lacks the resolution to define tract relationships to sphincters and levators. Fistulography is rarely needed now. Colonoscopy or barium enema should be considered when IBD or malignancy is suspected, when fistulas are recurrent or multiple, or in patients younger than 25 years. A small bowel series may occasionally be obtained for similar indications.
Treatment: Nonpharmacologic
Sitz baths can provide symptomatic relief and improve comfort.
Pharmacologic Therapy
Medications are rarely recommended as primary therapy. Immunomodulators such as infliximab may be used in selected cases, particularly when fistulas are related to Crohn disease.
Acute General Management
Surgery is the treatment of choice. Broad-spectrum antibiotics are used when cellulitis is present, when the patient is immunocompromised, or when valvular heart disease or prosthetic devices are present. Stool softeners or laxatives may be used to reduce straining and discomfort.
Chronic Management and Surgical Options
Definitive management is typically surgical, tailored to fistula type and complexity. The main goals are to eradicate the fistula, prevent recurrence, preserve sphincter function, and minimize healing time. Surgical and procedural options include fistulotomy, fistulectomy, seton placement (to maintain drainage while healing occurs), fibrin glue, fistula plugs, LIFT procedure (ligation of the intersphincteric fistula tract), rectal advancement flaps, and, in select complex situations, colostomy. Strategy varies by classification; superficial/intersphincteric and low transsphincteric fistulas are often candidates for fistulotomy, while higher or more complex fistulas more often require sphincter-sparing approaches such as setons, LIFT, advancement flaps, glue, or plugs. Extrasphincteric disease requires addressing any intraabdominal or pelvic source and is not managed with fistulotomy due to incontinence risk.
Disposition
Most patients are managed with outpatient surgery.
Referral
Referral to a surgeon experienced in anorectal fistula management is recommended.
Pearls and Considerations
HIV-positive and diabetic patients who develop perirectal abscesses or fistulas should be treated as true surgical emergencies. The risk of septicemia, Fournier gangrene, and other severe septic complications makes rapid evaluation and drainage imperative.
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