Anal Fissures are a common cause of perianal pain that has been a source of frustration to man and their physicians for thousands of years. The symptoms of pain and bleeding on defecation are very often erroneously attributed to haemorrhoidal disease, even by physicians themselves. It represents about 10 to 15% of referrals to any colorectal practice.
An Anal Fissure is essentially a tear or split in the anoderm at the dentate line. 80-90% of these are located in the posterior midline. Anterior midline locations are far less common, occurring in 5-10% of all cases. Symptoms of Anal Fissures often arise soon after the passage of a hard bowel movement through the anal canal. This is believed to cause stretching and subsequent tearing of the anoderm. Occasionally, this may be associated with a bout of severe diarrhoea. The anterior and posterior midlines are the weakest areas of the anal canal. It is at these locations that the external sphincter fibres decussate. In addition, the midline locations are areas where the skin is tethered more adherently to the sphincter complex. During the process of defecation, partial eversion of the anal canal leads to more tension arising in these areas. Coupled with the less adequate anodermal blood flow here, ischemia occurs and results in an ulcer being formed.
Once a fissure has formed, a cycle of repeated injury results. The resulting internal anal sphincter spasm tends to hold the edges of the ulcer apart, thereby preventing wound healing. Instead, further tearing of the mucosa tends to result with each bowel movement.
Only 2-5% of fissures are located in other locations and these should be viewed with suspicion. Common etiologies of these fissures include Crohn's disease, ulcerative colitis, and chronic infective processes such as anal tuberculosis, HIV infection and cancer. Patients who present with such atypical fissures should be referred to a colorectal surgeon for further evaluation. Biopsies of these fissures are mandatory.
Patients with anal fissures present with a very classical history of a 'searing' or 'tearing' type of pain which is associated with each bowel movement. This is usually accompanied by bright red per rectal bleeding. Symptoms of pruritus or perianal skin irritation may also be present.
Acute Anal Fissure
This is a superficial tear in the vertical axis of the squamous lining of the anal canal. Located between the anal verge and the dentate line, these tears may deepen to expose the underlying internal anal sphincter.
Chronic Anal Fissure
A fissure which fails to heal after 4 weeks is considered chronic. These fissures will have developed secondary changes which include the following:
Sentinel tag - these are hypertrophic skin tags at the distal edge of the fissure and are very commonly mistaken as external haemorrhoids and hence the misnomer 'sentinel pile'
Hypertrophic anal papilla
Induration of the edge of the fissure
Fibrosis of the exposed internal anal sphincter fibres
Relative stenosis secondary to spasm
It is imperative that the examining physician attempt to differentiate between anal fissures and haemorrhoids. Although this may be difficult at times, a properly performed physical examination of the perianal region is often revealing. Non prolapsing internal haemorrhoids can only be diagnosed through an anoscopic or proctoscopic examination. Attempting this in a patient with anal fissure is almost impossible without inflicting severe pain. Again, most fissures can be diagnosed by simple parting of the perianal skin.