Anal Fissure

What an anal fissure is

An anal fissure is a tear in the lining of the anal canal. It is one of the commonest causes of anal pain and bleeding, and it is often mistaken for piles. Most fissures lie in the midline at the back of the anal canal; a smaller number lie in the midline at the front.

A fissure is called acute in the early weeks and chronic when it has persisted, typically beyond about six to eight weeks, or when the edges have become thickened with a skin tag at the outer end and an enlarged papilla inside.

Why it happens

The usual sequence begins with trauma to the anal lining — a hard or bulky stool, repeated diarrhoea, straining, or childbirth. Pain then causes the internal anal sphincter to tighten. That raised resting pressure reduces blood flow to the same midline area where most fissures sit, and poor blood supply is why a tear that would normally heal quickly does not. Pain, spasm and poor healing keep each other going, which is why treatment aims at the spasm as well as the stool.

Typical symptoms

The pain is sharp and tearing during a bowel movement and often continues afterwards as a deep burning or throbbing ache for minutes to hours. Bright red blood is usually small in amount, seen on the paper or streaking the stool. Many people begin to put off going to the toilet because of the pain, which hardens the stool further and makes the next episode worse.

Assessment

Diagnosis is usually made from the history and a careful examination of the outside of the anus, gently parting the buttocks. A fissure in the typical midline position with typical symptoms does not usually need an internal examination at the first visit if that would be too painful; assessment can be repeated once the pain has improved.

Examination matters for another reason. A fissure that is off to the side, multiple, unusually large, painless, irregular or not healing is not a straightforward fissure. Those features raise the possibility of Crohn's disease, tuberculosis, sexually transmitted infection, HIV-related ulceration, or malignancy, and they warrant further assessment, which may include examination under anaesthesia and biopsy. Persistent bleeding, or bleeding with a change in bowel habit, weight loss or anaemia, needs investigation of the bowel in its own right rather than being attributed to the fissure.

First-line treatment

Non-operative treatment is the starting point and heals many fissures, particularly acute ones. It combines a high-fibre diet and adequate fluid, a stool softener or bulking agent so that stools pass without straining, and warm sitz baths, which relax the sphincter and ease pain.

Topical treatment is added to relieve the spasm. Calcium channel blocker ointments such as diltiazem, and nitrate ointments such as glyceryl trinitrate, both improve healing rates compared with placebo. Nitrates commonly cause headache, which is the main reason people stop using them; calcium channel blockers cause headache less often, and this influences which is chosen first in practice.

If the fissure does not heal

Botulinum toxin injection into the internal sphincter produces temporary chemical relaxation and is a recognised option for fissures that have not healed with topical treatment. It is not universally permanent, and it is not established as universally superior to other options; its effect wears off over time, and recurrence after it is well recognised.

Lateral internal sphincterotomy — dividing a small, controlled portion of the internal sphincter — has the highest healing rates for chronic fissure. It is commonly considered for chronic fissure that has not healed with medical treatment, and it may also be discussed earlier in carefully selected, pharmacologically naive patients after individualised assessment; earlier surgery is not routine and remains an individual decision. A tailored version of the operation, in which the division of the internal sphincter is limited to the length of the fissure itself rather than routinely extended to the dentate line, is described as providing similar healing with a lower rate of impaired continence than the conventional operation, which extends the division further.

LIS carries a recognised risk of altered control of wind or stool. The risk varies between patients and may be temporary or persistent, so baseline continence and sphincter-risk factors are assessed before surgery. Factors considered include previous obstetric sphincter injury, pre-existing continence symptoms, documented sphincter injury, inflammatory bowel disease and previous anorectal operations. Where sphincter division is undesirable because of these factors, sphincter-preserving alternatives such as an anal advancement flap may be discussed instead.

No treatment removes the underlying tendency. Fissures can recur, particularly if constipation and straining return, which is why the stool measures are continued after healing.

This section reflects the American Society of Colon and Rectal Surgeons clinical practice guideline for the management of anal fissures, which was published electronically on 1 November 2022 and appeared in the February 2023 print issue of Diseases of the Colon & Rectum.

What we do not claim

There is no treatment that guarantees a fissure will never come back. Laser treatment is not established in the ASCRS guideline as a guideline-preferred replacement for standard medical treatment, botulinum toxin or appropriately selected sphincterotomy; the word "laser" alone does not establish superior healing, lower recurrence or zero continence risk. Anyone offering a painless, permanent or guaranteed cure is overstating what the evidence supports.