Modern medicine believes that the formation of anal fissure is mainly caused by mechanical irritation and inflammatory changes in the anal skin and blood vessels.
①Anatomy: The external anal sphincter is divided into two parts from the coccyx forward to the back of the anal canal. It surrounds the anal canal forward along both sides of the anal canal, and joins the two parts to the front of the anal canal, leaving a gap in the front and back of the anal canal. Most of the levator ani muscle is attached to both sides of the anal canal. The front and back are less. The back and front of the anal canal are not as firm as both sides and are easily damaged. The back is more pressured by feces. The lack of blood supply to the midline of the posterior anal canal and the small elasticity are the causes of anal fissure.
②Injury: Dry feces can tear the skin of the anus. Frequent defecation during diarrhea can make the anal canal sensitive and tighten. Normal consistency can also cause injury. Chronic inflammation of the anal canal, proliferation of fibrous tissue, forming anal comb induration, hindering the relaxation of the sphincter, causing The anal canal is easily damaged and ruptured. Rectal foreign bodies, improper anal expansion methods, anal surgery, childbirth, congenital anal stenosis, proctocolitis, tuberculosis, etc. can also cause anal fissure.
③Infection: Acute and chronic anal sinusitis, anal papillitis, internal hemorrhoids and polyps are the main causes of infection. Infected pathogenic bacteria enter the anal gland through the orifice of the gland, forming an abscess in the subcutaneous tissue of the anal canal, and forming an ulcer after ulceration. Thrombophlebitis due to infection of small superficial thrombus can also cause anal fissure.
④ The cause of chronic anal fissure: it is not clear yet. It is generally considered to be related to the following aspects. First, anal fissures are mostly fusiform at the lower edge of the posterior sphincter of the anal canal, with only a small amount of edge overlapping with the lower part of the internal sphincter. The epithelium of the anal canal is repeatedly injured by defecation, making the anal fissure unhealed. Second, the reflex muscle pain and spasm caused by pain will cause local insufficiency of blood supply, delay the healing of anal fissures, and become chronic anal fissures. Third, there are embryonic remnant epithelial tissues deep in the anal canal. The skin of the anal canal is ruptured, exposing the epithelial cells in the submucosa to the bottom of the cleft. Due to the stimulation of foreign bodies from epithelial fragments on the cleft, repeated infections can easily form chronic anal fissures. .