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. Infection
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.
Signs and symptoms
Anal fistulae can present with the following symptoms:
skin maceration
pus, serous fluid and/or (rarely) feces discharge — can be bloody or purulent
pruritus ani — itching
depending on presence and severity of infection:pain
swelling
tenderness
fever
unpleasant odorThick discharge, which keeps the area wet

Diagnosis
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:

The opening of the fistula onto the skin may be observed
The area may be painful on examination
There may be redness
An area of induration may be felt; thickening due to chronic infection
A discharge may be seen

Classification
Parks classification: This was done by Parks et al. from the UK in 1976, before MRI or endoanal ultrasound was available. It classified the fistula in four grades:
St James University Hospital Classification: This was done by Morris et al. in the year 2000. This classification was improvement over Parks classification as it was based on MRI studies. It classified the fistula in five grades. Garg classification: This was done by Pankaj Garg in 2017. This classification is improvement over both Parks and St James University Hospital Classification. This was based on MRI studies and operative findings in 440 patients. It classified the fistula in five grades. The grades of this classification correlate quite well with the severity of the disease.