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 *Park's 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. Grade I & II are simpler fistulas and can be managed by Fistulotomy whereas Grade III-V are complex fistulas in which fistulotomy should be not be done. They should be managed by Fistula experts. Unlike Park's and St James University Hospital Classification, this correlation is quite accurate with Garg's classification. Therefore this new classification is useful to both surgeons and radiologists. Types Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types: *Extrasphincteric fistulae begin at the rectum or sigmoid colon and proceed downward, through the levator ani muscle and open into the skin surrounding the anus. Note that this type does not arise from the dentate line (where the anal glands are located). Causes of this type could be from a rectal, pelvic or supralevator origin, usually secondary to Crohn's disease or an inflammatory process such as appendiceal or diverticular abscesses. *Suprasphincteric fistulae begin between the internal and external sphincter muscles, extend above and cross the puborectalis muscle, proceed downward between the puborectalis and levator ani muscles, and open an inch or more away from the anus. *Transphincteric fistulae begin between the internal and external sphincter muscles or behind the anus, cross the external sphincter muscle and open an inch or more away from the anus. These may take a 'U' shape and form multiple external openings. This is sometimes termed a 'horseshoe fistula.' *Intersphincteric fistulae begin between the internal and external sphincter muscles, pass through the internal sphincter muscle, and open very close to the anus. *Submucosal fistulae pass superficially beneath the submucosa and do not cross either sphincter muscle. Differential diagnosis Other conditions in which infected perianal "holes" or openings may include pilonidal cyst.
Anal fistula
Anal fissure
Perianal hematoma
Perianal cellulitis
Anal cancer
Cimino fistula
Genital ulcer
Anal dysplasia