Anal Fistula

After an abscess has been drained, a tunnel may persist connecting the anal gland from which the abscess arose to the skin. In these cases, a fistula generally develops 4-6 weeks after the abscess has been drained, sometimes even months or years later.

A fistula may also develop from a misdiagnosed/mistreated anal rhagas, which becomes infected and shows itself outside the anus.
The presence of a fistula is generally indicated by persistent drainage from the outside opening.