An anal fissure is a tear in the mucosa (lining) of the anus.
It usually occurs in the midline most commonly towards the back of the anus.
A fissure usually results from a hard stool passing forcefully out of the anus without appropriate relaxation of the anal muscles.
There are two muscles in the anus that are in the shape of two cylinders one inside the other. The inside one is called the internal sphincter and is an involuntary muscle (you cannot relax or tense it willingly). The outside muscle is called the external sphincter and is a voluntary muscle (this is the muscle you use to stop yourself opening your bowels willingly).
An anal fissure (tear) causes a secondary spasm of the internal sphincter muscle. This in turn makes it harder for you to relax and pass a bowel motion further exacerbating constipation. It becomes a vicious cycle that needs to be broken by relaxing the internal anal sphincter.
Treatment of an anal fissure is aimed at softening the stools (see treatment of constipation) and relaxing the internal anal sphincter allowing the fissure to heal on its own.
Relaxation of the internal sphincter can be achieved by one of the following three options:
1. Topical ointment
- Applied 3 times a day.
- The most commonly used is called Rectogesic. This contains a substance called GTN which relaxes involuntary (smooth) muscle in the body including muscles in blood vessels. As a result, it commonly causes a mild headache. It should not be used during pregnancy. (2% Diltiazem is a better option for pregnant women)
- If this is not tolerated, other compounded (put together at compounding chemists) ointments are used. (0.5% Nifidipine + 5% Lignocaine – is most commonly used)
- Ointments should be tried for 6 weeks
2. Botox injection – Botulinum toxin A
- A 3ml injection containing up to 100 units of Botox is injected into the internal anal sphincter
- Although this can be done as an office procedure, it is best done under general anaesthetic which also allows better examination of the anus +/- any other required procedures such as debridement (cleaning-up) of the fissure.
- Botox works by relaxing the internal sphincter muscle for up to 3 months allowing the fissure to heal
- Botox is expensive ($500-$600) but may be covered at least partially by private health funds.
- This rarely causes temporary incontinence of flatus / liquid / solid stools.
3. Lateral sphincterotomy
- The lower part of the internal anal sphincter may be divided (up to one third of the muscle) to provide permanent relaxation of the muscle allowing for healing of the fissure and prevention of recurrence
- This is the most successful treatment. However, although the risk of incontinence is small, it is permanent.
You may be referred to a colorectal specialist surgeon if:
- The anal fissure is secondary to Crohn’s disease.
- The anal fissure is chronic and is not associated with spasm of the internal sphincter (low pressure fissures). Treatment may require excision of the fissure and a so-called advancement flap.