Internal anal sphincterotomy as an out-patient operation.

An acute fissure when observed by everting the anus *shows longitudinal muscle fibres in the floor of the ulcer. These are fibres of the conjoint longitudinal muscle layer which have passed downwards through the internal anal sphincter to gain attachment to the anal canal and perianal skin. If the lesion persists, the longitudinal fibres ulcerate through to expose the underlying whitish circular fibres of the internal sphincter. The edges are well defined and are undermined so that the true size of the ulcer is concealed. Infection is an important complication and its presence leads to the formation of the external skin tag and the hypertrophied anal papilla. The inflammation may progress to suppuration and the formation of a blind internal fistula, or rarely, it may track externally to form a complete low anal fistula. Division or stretching of the circular muscle -fibres of the internal sphincter exposed in the floor of a fissure-in-ano relieves the pain characteristic of the lesion and results in healing.