Anal fissure

An anal fissure causes suffering out of all proportion to its size. It starts as a crack in the lower part of a patient's anal canal, which makes defaecation, and the half-hour following it, acutely painful. Even the thought of a bowel movement may fill him with such fear that he ignores the urge, so that the hard constipated stools that he eventually passes make his fissure worse, and may occasionally make it bleed.

You will almost always find his fissure posteriorly in the 6 o'clock position, between his anal verge and his pectinate line, directly over the distal end of his internal sphincter. A small oedematous skin tag commonly forms on his anal verge, just posterior to the fissure. This is the ''sentinel skin tag'. Later, his fissure may become indurated and infected, and may lead to a low perianal abscess (5.13), which may discharge through the fissure, and externally, to produce a low anal fistula. His internal sphincter lies directly under his fissure, and after several months of exposure this becomes fibrosed and spastic.

ANAL FISSURE DIAGNOSIS. A fissure is acutely painful, so don't do a rectal examination, or pass a proctoscope, until the patient is under general anaesthesia. Alternatively, and less satisfactorily, smear his anus with 10% amethocaine ointment for 10 minutes. Can you see a sentinel skin tag? Look for a triangular or pear-shaped slit posteriorly, just inside his anus.

DIFFERENTIAL DIAGNOSIS Other obvious skin changes and cracks? (pruritus ani). Diarrhoea with multiple fistulae away from the midline? (the skin changes following some forms of colitis). More induration than in a fissure, a larger ulcer, and perhaps enlarged inguinal nodes? (carcinoma). Indurated margins, a symmetrical lesion on the opposite margin of his anal canal, and no pain? (primary chancre). The whole region is moist and pruritic, with flat, slightly-raised lesions, which are usually symmetrical on both sides? (secondary syphilis).

TREATMENT depends on how long he has had his fissure. Early presentation is unusual in the developing world.

If it is acute (less than 10 days old), only his epithelium is involved. It may heal, if you keep his stools soft for a week or two with liquid paraffin. When it has healed, warn him that it may return, if he allows himself to become constipated. He may have to continue this treatment indefinitely. Warn him that he must not keep his stools too loose, or they will never dilate his anus, so that it stenoses.

If you give him a local anaesthetic ointment (5% lignocaine), ask him to smear it over the sphincter inside his anus, not outside it.

If, his fissure fails to heal after you have kept his stools soft for 3 weeks, stretch his anus (22.5). Unfortunately the relapse rate with non-operative treatment is high, even if a fissure does heal at first.

If his fissure is chronic (more than 10 days), fibrosed, has a sentinel skin tag, and especially if you can see the exposed fibres of his internal sphincter under it, it will probably not respond to non-operative treatment. First try stretching his anus (22.5). After a day or two, there is a 95% chance that he will be completely free of pain. There is a 15% chance that his fissure will recur later. If it does, don't repeat the stretching, refer him for sphincterotomy.