An anal fissure involves stretching and tearing of the rim of the anus. It may result from several possible causes, or present in various circumstances. These include:
- a lot of pressure on the area, for example due to passing very hard or impacted stools
- damage or weakness to the skin, causing it to break easily.
In most cases, the skin damage around the anus will heal without significant complications. However, some individuals are more susceptible to recurrent breakdown of the anal skin, or to the development of a non-healing fissure. The reasons may vary from the extremely high muscle tone of the anal sphincter that increases the tightness of the anus, to reduced blood flow in the anal area. As a result, an anal fissure can develop or persist, and cause significant pain.
It is a relatively common condition that is estimated to affect 1 in 10 individuals at some point throughout their lifetime. Both males and females are affected equally, and individuals of any age may develop an anal fissure.
Some of the usual causes are discussed below.
The most common cause of an anal fissure is abnormal stools or bowel movements. In particular, large or hard stools are more difficult to pass and place greater stress on the anus during bowel movements.
Individuals who are constipated and need to strain to pass stools are most likely to be affected, as the impacted stool increases the risk of tearing the anal margin. An anal fissure can also sometimes occur if an individual has severe or chronic diarrhea, due to the inflamed mucosa and perianal skin.
High muscle tension in the anal sphincter
Some individuals have a spastic anal sphincter which makes it very difficult to pass normal stools without pain and tears of the anal mucosa and skin. In addition, this muscle hypertrophy leads to reduced blood supply to the skin around the anus, leading to slow healing of occasional tears and resulting in an anal fissure.
Anal fissures are also more common in women following childbirth, which is estimated to account for approximately 10% of cases. This is most likely due to the straining required during childbirth that can put greater pressure on the anus and may result in an anal tear.
Crohn’s Disease or Inflammatory Bowel Diseases
Inflammation of the anorectal area can also increase the risk of an anal fissure developing. The inflammatory bowel condition called Crohn’s disease is associated with inflammation of the intestinal tract. This can lead to more pressure on the anal canal, and weaken the skin around the anal orifice, so that it is more likely to tear.
In rare cases, an anal fissure may be caused by an infection of the anus, which weakens the skin due to the inflammation. This may include infections such as:
Individuals who engage in anal intercourse are at a greater risk of acquiring such infections and developing an associated anal fissure.
Rarely, an anal fissure may develop as a result of cancer of the rectum or anus. The tumor growth probably weakens the skin or causes obstruction to the passage of stools, leaving the anus more vulnerable to tearing.
There are some cases of anal fissure without a clear identifiable cause. These are referred to as idiopathic anal fissure.
Age-related Risk Factors
Both the very young and the elderly are at an increased risk of anal fissures in comparison to the general population.
Infants are more likely to experience an anal fissure than other individuals, although the reason for this relationship is not clear. It appears that the first year of life is the time associated with the greatest risk of anal fissure.
Conversely, elderly individuals are also more likely to be affected. This is thought to be at least in part due to reduced circulation to the rectal area, which may result in skin breakdown and an anal fissure.