Use of hydrogen peroxide to identify internal opening of anal fistula and perianal abscess.

Hydrogen peroxide injected into a fistula or perianal abscess produces a jet of white bubbles from the internal orifice on the dentate line. This technique has been helpful in locating this often elusive ostium. Failure to produce such an efflux warns one that the pathology was different from what was expected. Confidence to abandon the search in the absence of an efflux is developing, provided the dictates of gravity are respected in positioning the patient so that the anus lies above the abscess.