Things You Need to Know about Anal Fistula: Causes and Types
What is an anal fistula?
An anal fistula is a small abnormal tunnel/cavity/tract that forms between the end of the bowel (anal canal) and the perianal skin. This occurs due to an infection surrounding the anus causing an accumulation of pus (perennial abscess) or infection/clogging of the anal glands. The track keeps draining leading to discomfort and irritation of the skin or may get temporarily blocked forming a boil/abscess.
Causes of anal fistula:
The common causes include clogged anal glands, inflammation of these glands, and perianal abscesses.
The less common causes include Crohn’s disease, diverticulitis, ulcerative colitis, sexually transmitted diseases, trauma, infection such as tuberculosis and HIV, radiation, hidradenitis suppurativa, a surgery complication near the anus, and cancer of the large bowel.
Additionally, the causes for rectovaginal fistula include complications/injury caused during childbirth, impacted feces, and sexual abuse. For rectovesical fistula, the causes include a post transurethral resection of the bladder and post surgical procedures of prostate cancer.
The cause of colorectal fistula is mostly due to the disease of the diverticula and it may also be due to colorectal cancer. Diverticulitis is the commonest cause of vesicointestinal fistula.
Types of fistula:
Depending upon the tissue through which the track travels-
- Intersphincteric fistula: The tract passes between the internal and external anal sphincter and opens near to the anus.
- Transphincteric fistula: The tract crosses the external and internal sphincter and usually opens one or two inches away from the anus. It may create a horseshoe (U shape) fistula and may create multiple openings on either sides of the anus.
- Suprasphincteric fistula: The tract travels between the internal and external anal sphincters and goes above and beyond the puborectal muscle. It transverses the puborectal muscle and goes downward between the puborectal and levator ani muscles and opens one or two inches away from the anus.
- Extrasphincteric fistula: The tract stars at the rectum or sigmoid colon and goes downward, through the levator ani muscle which leads to an opening into the skin near the anus. These types of fistulas are due to Crohn’s disease, diverticular abscess, and appendiceal abscess.
- Rectovaginal fistula: An abnormal connection between the vagina and rectum. The cavity formed lets stool and gas pass from the bowel into the vagina. It is classified as a simple or complex fistula based on size, location, and etiology.
- Small rectovaginal fistulas have a size less than 2.5 cm in diameter.
- Large rectovaginal fistulas have a size of more than 2.5 cm in diameter.
- Low rectovaginal fistulas: also called anovaginal fistula. The vaginal opening is near the vaginal fourchette.
- High rectovaginal fistulas: the vaginal opening is situated at the level of the cervix.
- Middle rectovaginal fistulas: the vaginal opening is between low fistulas and high fistulas.
Simple rectovaginal fistulas: small, low fistulas due to infection or trauma.
Complex rectovaginal fistulas: large, high fistulas due to inflammatory bowel diseases. Recurrent fistulas also fall into the complex category.
- Rectovesical fistula: An abnormal connection between the urinary bladder and rectum. The cavity formed lets stool and gas pass from the bowel into the urinary bladder.
- Colovesical fistula: A rare fistula where there is an abnormal communication between the colon and the bladder. This causes stool and gas to pass from the colon into the bladder.
- Vesicointestinal fistula: An abnormal connection between the urinary bladder and intestine.
If you require anal fistula treatment, find the best proctologist at Shreyas Ano Rectal Hospital and Research Center (www.proctocure.com) to receive the best fistula treatment in India.