diagnosis of anal fistula
Last reviewed 01/2018
Anal fistula should be suspected in patients presenting with chronic or recurrent perianal pain, lump, or discharge.
Inquire about:
- recurrent abscess or failure of healing at an incision and drainage site
- about previous perianal sepsis, surgery or radiotherapy, trauma (obstetric or otherwise), and other conditions which are associated with anal fistula
Examination:
- inspection of the perianal area for an external opening
- it may appear as a simple pit in the skin or may be obviously discharging, with or without a surrounding rim of raised granulation tissue
- or it may appear within the scar of a previous abscess
- palpation of the perianal area with a lubricated finger
- a palpable track maybe felt like a cord-like structure beneath the skin
- digital rectal examination
- may detect indentation or induration (often described as "a grain of rice")
- adequate in most patients with a simple fistula (in those with a
more complex fistula, it should be interpreted in the light of imaging,
particularly MRI
- examination under anaesthesia
- allows a thorough assessment of the fistula opening
Imaging
- endoanal ultrasound
- operator dependent
- provides anatomical detail of the tracks and the sphincters
- injection of hydrogen peroxide into fistula tracks improves accuracy
- MRI
- considered the gold standard
- indicated in
- all recurrent fistulas
- primary fistulas that appear to be complex after examination under anaesthesia or endoanal ultrasound.
- anal manometry
- provides objective assessment of sphincter function by measuring the anal canal pressure
- may have a role in in patients with compromised continence or those at risk (e.g. - patients with a history of sphincter surgery or injury)
Reference: