Anal fistula is a chronic abnormal communication between the anal canal and the perianal skin. An anal fistula can be described as a narrow tunnel with its internal opening in the anal canal and its external opening in the skin near the anus. Anal fistulae commonly occur in people with a history of anal abscesses. They can form when anal abscesses do not heal properly.
 Anal fistulae originate from the anal glands, which are located between the internal and external anal sphincter and drain into the anal canal. If the outlet of these glands becomes blocked, an abscess can form which can eventually extend to the skin surface. The tract formed by this process is a fistula.
 Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It can then extend to the surface again – repeating the process.
 Anal fistulae per se do not generally harm, but can be very painful, and can be irritating because of the drainage of pus (it is also possible for formed stools to be passed through the fistula). Additionally, recurrent abscesses may lead to significant short term morbidity from pain and, importantly, create a starting point for systemic infection.
 Treatment, in the form of surgery, is considered essential to allow drainage and prevent infection. Repair of the fistula itself is considered an elective procedure which many patients opt for due to the discomfort and inconvenience associated with an actively draining fistula.
 Anal fistulae can present with the following symptoms:
 Diagnosis is by examination, either in an outpatient setting or under anaesthesia (referred to as EUA or Examination Under Anaesthesia). The fistula may be explored by using a fistula probe (a narrow instrument). In this way, it may be possible to find both openings. The examination can be an anoscopy. Diagnosis may be aided by performing a fistulogram, proctoscopy and/or sigmoidoscopy.
 Possible findings:
 Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types:
 Other conditions in which infected perianal "holes" or openings may include pilonidal cyst.
 There are several stages to treating an anal fistula:
 Definitive treatment of a fistula aims to stop it recurring.  Treatment depends on where the fistula lies, and which parts of the internal and external anal sphincters it crosses. However, treatment is challenging as complete eradication of the anal sphincters may lead to continence impairment, but failure to excise the affected areas results in recurrence. Those already treated for recurring anal fistula are at higher risk to experience re-recurrence of the disease. 
 The VAAFT procedure is done in 2 phases, diagnostic and operative. Before the procedure, the patient is given a spinal or general anaesthetic and is placed in the lithotomy position (legs in stirrups with the perineum at the edge of the table).  In the diagnostic phase, the fistuloscope is inserted into the fistula to locate the internal opening in the anus and to identify any secondary tracts or abscess cavities. The anal canal is held open using a speculum and irrigation solution is used to give a clear view of the fistula tract. Light from the fistuloscope can be seen from inside the anal canal at the location of the internal opening of the fistula, which helps to locate the internal opening.  In the operative phase of the procedure, the fistula tract is cleaned and the internal opening of the fistula is sealed. To do this, the surgeon uses the unipolar electrode, under video guidance, to cauterise material in the fistula tract. Necrotic material is removed at the same time using the fistula brush and forceps, as well as by continuous irrigation. The surgeon then closes the internal opening from inside the anal canal using stitches and staples.
 Some people will have an active infection when they present with a fistula, and this requires clearing up before definitive treatment can be decided.
 Antibiotics can be used as with other infections, but the best way of healing infection is to prevent the buildup of pus in the fistula, which leads to abscess formation.  This can be done with a seton.
 A literature review published in 2018 showed an incidence as high as 21 people per 100,000. "Anal fistulas are 2–6 times more prevalent in males than females, with the condition occurring most frequently in patients in their 30s and 40s."