Your Health A-Z

Anal fissure


Anal fissure is a small tear in the lining of the lower part of the anal canal. It usually occurs in the midline posteriorly.


Most fissures are due to local trauma, the commonest being damage caused by passing large hard stools. Prolonged diarrhoea can also cause fissure formation. The site of the fissure is thought to be due to poor blood supply in that area.

Once the tear occurs, the anal sphincter muscle, which ordinarily acts like a valve, goes into spasm. This increases the pain, and tears the fissure even more open. Subsequent (painful) passage of stool can then cause even more damage. This can set up a vicious cycle, leading to a chronic fissure.


The diagnosis of anal fissure is clinical – the history of a tearing pain during defecation is typical, and gentle examination by spreading the buttocks apart will reveal the fissure. Patients are usually in too much pain to tolerate a rectal examination or proctoscopy.


Constipation is present in most patients, and it must be established whether this is dietary, or has more sinister underlying causes. Most patients will have a history of past or present haemorrhoids, also associated with constipation. Recurrent fissures, or those found in atypical positions warrant investigating, as there is a known association with Crohn’s disease, a chronic inflammatory condition of the bowel.


The immediate aim is to provide pain relief, and prevent infection. Topical anaesthetic creams can be used.

The ultimate aim of treatment is to break the cycle of constipation-fissure formation-pain-more constipation-more fissure formation. Soft stools are important, and there are various preparations (mostly fibre-containing) available for this, according to the patient and doctor’s preference. The patient is encouraged to change dietary habits to promote normal stool formation. Warm sitz baths after bowel actions help to relax the anal sphincter and promote hygiene.

Other treatments which have been tried include drugs such as nifedepine, nitroglycerin and diltiazem, especially in chronic fissures. The results are not significantly better than those obtained with the combination of normalising stool consistency and sitz baths.

The vast majority of patients heal on medical therapy alone. However, for the few chronic or recurrent cases, other options exist. Injecting of botulinum toxin (Botox) may help to stop the muscle spasm of the sphincter. Many patients benefit from this, but there is a risk of excess paralysis causing faecal incontinence.

If medical treatment fails, surgery may be considered. A Lord’s dilatation procedure is often done, but has a high incidence of post-operative sphincter tears and incontinence. Alternatively, a lateral sphincterotomy is done to relax the muscle. This almost always heals the fissure, but there is a significant risk of faecal incontinence, especially if done by an inexperienced surgeon. One study reports that even five years after surgery, 6 percent of patients were still incontinent of faeces. Surgery is thus reserved for those cases which do not resolve despite adequate, sustained medical therapy.

During surgery, the fissure itself is not excised, but may be biopsied if it has an appearance suggesting malignancy.

(Dr AG Hall, Health24, January 2008)

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