Anal fissure

Definition

An anal fissure (syn. fissure in ano) is an elongated ulcer in the long axis of the lower anal canal.

Location

The site of election for an anal fissure is the midline posteriorly (90 per cent overall). The next most frequent situation is the midline anteriorly.

Aetiology

The cause of anal fissure, and particularly the reason why the midline posteriorly is so frequently affected, is not completely understood. A probable explanation is as follows: the posterior wall of the rectum curves forwards from the hollow of the sacrum to join the anal canal, which then turns sharply backwards. During defecation the pressure of a hard faecal mass is mainly on the posterior anal tissues, in which event the overlying epithelium is greatly stretched and, being relatively unsup­ported by muscle, is placed in a vulnerable position when a scybalous mass is being expelled. Possibly some cases are due to tearing down of an anal valve of Ball. An anterior anal fissure is much more common in women, particularly in those who have borne children. This can be explained by the lack of support of the anal mucous membrane by a damaged pelvic floor and an attenuated perineal body. A more recent

suggestion supported by Doppler flow studies is that a fissure is due to ischaemia. It may be that the cause is a combination of trauma initially perpetuated by a poor blood supply.

Some causes of anal fissure are certain:

an incorrectly performed operation for haemorrhoids in which too much skin is removed. This results in anal stenosis and tearing of the sear when a hard motion is passed;

       inflammatory bowel disease — particularly Crohn’s disease;

  sexually transmitted diseases.

Pathology

An anal fissure is either acute or chronic. The upper internal end of the fissure stops at the dentate line. Because the fissure occurs in the stratified sensitive epithelium of the lower half of the anal canal, pain is the most prominent symptom (see below).

Acute anal fissure is a deep tear through the skin of the anal margin extending into the anal canal. There is little inflammatory induration or oedema of its edges. There is accompanying spasm of the anal sphincter muscle.

Chronic anal fissure is characterised by inflamed indurated margins, and a base consisting of either scar tissue or the lower border of the internal sphincter muscle. The ulcer is canoe-shaped, and at the inferior extremity there is a tag of skin, usually oedematous. This tag is known picturesquely as a sentinel pile — ‘sentinel’ because it guards the fissure. There may be spasm of the involuntary musculature of the internal sphincter. In long-standing cases, this muscle becomes organ­ically contracted by infiltration of fibrous tissue. Infection is common and may be severe, ending in abscess formation. A cutaneous fistula may follow.

Chronic fissure in ano may have a specific cause — often a granulomatous infection, e.g. Crohn’s disease. Biopsy exami­nation is advisable of any tissue removed at operation for a chronic fissure. Specific fissures of this type are often less painful than the appearances of the lesion would suggest.

Clinical features

1 Symptoms of anal fissure

2 Pain on defecation

3 Bright red bleeding

4 Mucus discharge

5 Constipation

The condition is more common in women and generally occurs during the meridian of life. It is uncommon in the aged, because of muscular atony, whereas anal fissure is not rare in children, is sometimes encountered during infancy and may cause acquired megacolon (Chapter 57).

  Pain is the symptom — sharp, agonising pain starting during defecation, often overwhelming in intensity and lasting for an hour or more. As a rule, it ceases suddenly, and the sufferer is comfortable until the next action of the bowel. Periods of remission occur for days or weeks. The patient tends to become constipated rather than go through the agony of defecation. (One patient accustomed himself to take a generous dose of senna on Saturday night, and retire to the toilet on Sunday morning with a bottle of whisky and the newspaper.)

  Bleeding — this is usually slight and consists of bright streaks on the stools or the paper.

  Discharge. A slight discharge accompanies fully established cases.

On examination

In cases of some standing, a sentinel skin tag can usually be displayed. This, together with a typical history and a tightly closed, puckered anus, is almost pathognomonic of the con­dition. By gently parting the margins of the anus, the lower end of the fissure can be seen (Fig. 61.23).

Because of the intense pain it causes, digital examination of the anal canal should not be attempted at this stage unless the fissure cannot be seen, or it seems imperative to exclude major intrarectal pathology. In these circumstances, the local application of a surface anaesthetic such as 5 per cent xylocaine on a pledget of cotton wool, left in place for about 5 minutes, will enable the necessary examination to be made. In early cases, the edges of the fissure are impalpable; in fully established cases, a characteristic crater which feels like a vertical buttonhole can be palpated. The diagnosis must be established beyond doubt, for which a general anaesthetic may be required.

Differential diagnosis

Carcinoma of the anus in its very early stages easily simulates a fissure. If real doubt exists, the lesion must be excised under general anaesthesia and submitted to histological examination.

Multiple fissures in the perianal skin are commonly seen as a complication of skin diseases, scratching and inflammatory bowel disease, as well as homosexual practices (sodomy, fluting and the use of anorectal sex toys; Fig. 60.8) and anorectal sexually transmitted disease such as herpes. Admitted homosexuals, should, after appropriate counselling, be offered a human immunodeficiency virus (HIV) test as they may have acquired immunodeflciency syndrome (AIDS) (Chapter 9).

Tuberculous ulcer has an undermined edge.

Proctalgia fugax (see below) causes severe episodic pain.

Treatment

The pain of an anal fissure is so great that usually the patient demands relief, and consequently many patients with an acute fissure present early. The object of all treatment for this condition is to obtain complete relaxation of the internal sphincter. Provided the complications are dealt with, the fissure will slowly heal as soon as all spasm has disappeared.

Conservative treatment

Because of the risks of incontinence associated with sphincterotomy, it is now usual practice to treat anal fissures conser­vatively in the first instance using a chemical sphincterotomy. Nitric oxide has been shown to be the neurotransmitter which induces relaxation of the internal sphincter. Glyceryl trinitrate, being a nitric acid donor, when applied as an ointment (0.2 per cent by weight) to the anal canal produces sufficient relaxation of the sphincter to allow the fissure to heal in up to two-thirds of patients (Scholefield). In addition, glyceryl trinitrate ointment improves blood flow to the area, and this aids healing. Unfortunately, glyceryl trinitrate ointment may produce severe headaches and other agents with fewer side effects should be available soon. Other measures include laxatives to ensure the motions are soft, but the stools should not be made watery. Celevac tablets give a soft stool of good bulk which is ideal. Anal dilators used in con­junction with xylocaine ointment are difficult to insert because of pain and are rarely effective.

Operative measures. The simplest procedure in the past has been gentle dilatation of the sphincter. Under general anaesthesia, the index and middle finger of each hand were inserted simultaneously into the anus and carefully pulled apart dilating the anus so that its diameter was no greater than four finger breadths. Great care and judgement had to be exercised, so that the anal sphincter was not overstretched. The risks of incontinence following this procedure have now made it unpopular. Although it might still be used for young men with high pressure sphincters who understand the slight risk, it is definitely contraindicated in those patients with weak sphincters.

Should these measures prove ineffective, or if the fissure is chronic with fibrosis, a skin tag or a mucous polyp, then surgical measures are advisable. General anaesthesia is best, although some surgeons use a local anaesthetic in the form of xylocaine or lignocaine introduced into the ischiorectal fossa on each side, in order to anaesthetise the nerves passing towards the rectum. In other situations, a caudal anaesthetic is suitable.

Lateral anal sphincterotomy (Notaras). In this operation, the internal sphincter is divided away from the fissure itself — usually either in the right or the left lateral positions. The procedure can be done by an open or a closed method. Healing is usually complete within 3 weeks. The operation is more successful for acute than chronic fissures. Seventy-five per cent of cases are suitable for treatment by this method, which can be done as an out-patient procedure under local anaesthesia by an experienced surgeon. However, there is a definite yet small risk of incontinence and it is imperative that patients are appraised of this risk preoperatively.

Dorsal fissurectomy and sphincterotomy. The essential part of the

operation is to divide the transverse fibres of the internal sphincter in the floor of the fissure. If a sentinel pile is present, this is excised. The ends of the dividend muscle retract and a smooth wound is left. The after-treatment consists of attention to bowels, a daily bath and the passage of an anal dilator until the wounds have healed, which usually takes about 3 weeks. Despite the presence of the wound, there is little or no pain and the results are good. The disadvantage of this operation is the prolonged healing time — usually not less than 3 weeks and often longer — and, occasionally, a mild, persistent and permanent mucus discharge. It is now reserved only for the most chronic or recurrent anal fissures, the majority being treated by lateral sphincterotomy. Once again incontinence might be a postoperative complication.

Hypertrophied anal papilla

Anal papillae occur at the dentate line, and are remnants of the ectoderma) membrane that separated the hindgut from the proctodaeum. As these papillae are present in 60 per cent of patients examined proctologically, they should be regarded as normal structures. Anal papillae can become elongated, as they frequently do in the presence of an anal fissure. Occasionally, an elongated anal papilla may be the cause of pruritus. An elongated anal papilla associated with pain and/or bleeding at defecation is sometimes encountered in infancy. Haemorrhage into a hypertrophied anal papilla can cause sudden rectal pain. A prolapsed papilla may become nipped by contraction of the sphincter mechanism after defecation. Occasionally, a red oedematous papilla is encountered with local pain and a purulent discharge from the associated crypt. This condition of `cryptitis’ may be cured by laying open the mouth of the infected anal gland and removing the papilla.

Treatment. Using a slotted proctoscope, elongated papillae without haemorrhoids should be crushed and excised after injecting the base with local anaesthetic. When large papillae complicate internal haemorrhoids, this is an indication for operative treatment of the haemorrhoids, as well as excision of the elongated papillae.

Proctalgia fugax

This disease is characterised by attacks of severe pain arising in the rectum, recurring at irregular intervals and apparently unrelated to organic disease. The pain is described as cramp-like, often occurs when the patient is in bed at night, usually lasts only for a few minutes and disappears spontaneously. It may follow straining at stool, sudden explosive bowel action or ejaculation. It seems to occur more commonly in patients suffering from anxiety or undue stress, and also it is said to afflict young doctors. The pain may be unbearable — it is possibly due to segmental cramp in the pubococcygeus muscle. It is unpleasant, incurable, but fortunately harmless and gradually subsides. A mote chronic form of the disease has been termed the ‘levator syndrome’ and can he associated with severe constipation. Biofeedback techniques have been used to help such patients: some surgeons have been willing to sever the puborectalis muscle, but this can cause incontinence.