Anal fistula overview

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Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Anal fistula from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

History and Symptoms

Physical Examination

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Laboratory Findings

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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

Anal fistula develops from infection of anal crypts gland. The initial infection occurs in the ducts of the anal glands and the spread of infection results in the formation of the abscess.If the abscess is ruptured, a fistula is formed. Anal fistulas are associated with following conditions are diverticulitis, foreign-body reactions actinomycosis, chlamydia, lymphogranuloma venereum (LGV), syphilis, tuberculosis, radiation exposure, HIV disease, [[crohn's disease|Crohn’s disease, pilonidal disease, hidradenitis suppurativa, trauma, previous surgery (including ileoanal pouch surgery), presacral dermoid cysts, sacrococcygeal teratoma.

Causes

Anal fistula is caused by crohn's Disease, obstetric injury, retained foriegn body in rectum, radiation proctitis, gonorrhea, HIV, cryptitis, lymphogranuloma venerum, perirectal abscess sequelae of rupture or surgery, syphilis, thrombosed hemorrhoids, tuberculosis, ulcerative Colitis.

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

The prevalence of anal fistula is approximately 1-2 per 10,000 individuals worldwide. In England, the incidence of anal fistula is approximately 18.4 per 10,0000 per year. Anal fistula commonly affects individuals in the third, fourth, and fifth decades, with a peak around 40 years of age. Men are twice more commonly affected by anal fistula than women.

Risk Factors

Common risk factor in the development of anal fistula are diabetes, smoking, alcohol, obesity.

Screening

According to The American Society of Colon and Rectal Surgeons, screening for the anal fistula is not recommended.

Natural History, Complications, and Prognosis

Anal fistula usually develops in 20-30 years of age and peaks around 40 years. If left untreated, patients with anal fistula may progress to develop the perianal abscess and cancer. Common complications of anal fistula include:urinary retention, bleeding, perianal abscess, fecal incontinence, carcinoma. Prognosis is excellent after surgery and recurrence rate is 7-2

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.

Primary Prevention

Adequate treatment of crohn's disease, HIV infection, actinomycosis, cryptitis, gonorrhea,syphilis, tuberculosis and ulcerative Colitis. Maintaining proper hygiene.

Secondary Prevention

There is no secondary prevention associated with anal fistula.

References

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