Anal fistula overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
An anal fistula is an abnormal connection between the epithelialised surface of the anal canal and (usually) the perianal skin. (See definition of a fistula).
Anal fistulae originate from the anal glands, which are located between the two layers of the anal sphincters and which drain into the anal canal. If the outlet of these glands becomes blocked, an abscess can form which can eventually point to the skin surface. The tract formed by this process is the fistula.
Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It then points to the surface again, and the process repeats.
Anal fistulas per se do not generally harm and they often do not hurt, but they can be irritating because of the pus-drain; additionally, recurrent abscesses may lead to significant short term morbidity from pain, and create a nidus for systemic spread of infection.
Surgery is considered essential in the decompression of acute abscesses; repair of the fistula itself is considered an elective procedure which many patients elect to undertake due to the discomfort and inconvenience associated with a draining tract.
Historical Perspective
In 1880, Herman and Desfosses described the anal glands within the internal sphincter, sub-mucosa and their opening into the anal crypts and demonstrated that the infection of these glands and the spread of the infection through the intersphincteric space can result in the formation of a anorectal abscess. In 1900, Goodsall found a rule of thumb that uses the location of fistula for the treatment of fistula.
Classification
Anal fistula are classified into four types based on the relationship to sphincter- Intersphincteric, Transsphincteric, Suprasphincteric, Extrasphincteric. Anal fistula are classified into two categories based on the risk factors associated- Simple anal fistula and Complex anal fistula. Anal fistulas are also classified according to primary tracks into two- high and low anal fistulas.
Pathophysiology
Causes
Differentiating Anal fistula overview from Other Diseases
Anal fistula must be differentiated from other causes of anal pain including anal fissure, thrombosed hemorrhoids, levator spasm, sexually transmitted disease, proctitis, hidradenitis suppurativa, infected skin furuncles, herpes simplex virus, tuberculosis, syphilis, actinomycosis and cancer.
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications, and Prognosis
Diagnosis
Diagnostic Criteria
There is no diagnostic criteria associated with anal fistula.
History and Symptoms
The hallmark of anal fistula is rectal pain during defecation, sitting and cough. A positive history of Crohns disease, Rectal abscess, Obstetric injury and prior anorectal injury is suggestive of anal fistula. Common symptoms are intermittent rectal pain during defecation, sitting and any activity, pain is throbbing in quality and sometimes occur throughout the day and resolved by opening the track, recurrent perianal malodourous discharge, perianal bloody discharge, perianal pruritis. Less common symptoms of anal fistula are fever and pain referred to thighs, low back, or buttocks.
Physical Examination
Patients with anal fistula usually appear in distress due to throbbing rectal pain. Patient presents with anal fistula is having normal vital signs but if anal fistula gets infected, it will lead to the formation of an abscess. Patient with an abscess presents with unstable vitals like High-grade fever, tachycardia, tachypnea, low blood pressure. On rectal examination, there is redness, tenderness and discharge is seen.
Laboratory Findings
There are no diagnostic laboratory findings associated with anal fistula. The anal fistula is mostly diagnosed clinically but in case of complication like the anal abscess, tests done are - complete blood count with differentials, blood culture, ESR, wound culture.
X-ray
There are no x-ray findings associated with anal fistula.
CT scan
There are no CT scan findings associated with anal fistula.
MRI
MRI is the gold standard imaging study to know about fistula anatomy. Indications are recurrent fistulas and complex fistulas.
ECG
There are no ECG associated with anal fistula.
USG
Endoanal ultrasound used to know details of fistula anatomy, tracks, and the spinchters.This is used intraoperatively by surgeons to have better information of fistula. Accuracy of endoanal ultrasound is improved by injection of hydrogen peroxide into fistula tracks. Ultrasound has a limited use because probe can go 2 cm from the anus so it is poor at evaluating pathology beyond the sphincters
Other Imaging Findings
There are no other imaging findings associated with anal fistula.
Other Diagnostic Studies
There are no other diagnostic studies associated with anal fistula.
Treatment
Medical Therapy
Pharmacotherapy used in anal fistula depends upon the location and symptoms of patient. Antibiotics are used in patient with comorbities like immunosuppression, diabetes, extensive cellulitis, prosthetic devices and high risk cardiac patients. Antipyretics and analgesic for symptomatic relief of pain and fever. Treatment of underlying causes is important to treat recurrent anal fistulas.
Surgery
The mainstay of treatment of anal fistula is surgical treatment.The principles for the management of anal fistula are described by the acronym SNAP, which stands for sepsis, nutrition, anatomy, and procedure according to British Medical Journal. Various methods of surgery are Fistulotomy and Seton. Sphincter-saving methods are Fibrin glue, Endorectal advancement flap, LIFT procedure, BioLIFT, Stem cells and Defunctioning.