Anal fistula / fistula-in-ano, is an inflammatory track which has an external opening (secondary opening) in the penanal skin and an internal opening (primary opening) in the anal canal or rectum. This track is lined by unhealthy granulation tissue and fibrous tissue.
CAUSE.(a) The fistula usually originates from a perianal abscess in the intersphincteric space of the anal canal from infection of the anal gland. As the anal gland is situated deep to the internal sphincter its duct passes through the internal sphincter to open in the crypts of Morgagni situated on the dentate line. Due to the tone of the internal sphincter the duct cannot aptly discharge the contents of the gland. Stasis and secondary infection lead to abscess formation from the anal gland in the intenphincteric region. From here the mtemal opemng traverse through the internal sphincter to open into the anal canal and the abscess usually tracks down and opens in the perianal skin extcmally thus fistula-in-2mo is formed. Several other disorders may be conw'dvrvd which may cause fistula in ano. These are :