• Clinical science

Anal fissures


An anal fissure is a longitudinal tear of the perianal skin distal to the dentate line, often due to increased anal sphincter tone. Anal fissures are classified according to etiology (e.g., trauma or underlying disease) or duration of disease (e.g., acute or chronic). They are typically very painful and may present with bright red blood per rectum (hematochezia). Anal fissures are a clinical diagnosis based on history and examination findings. Management is primarily conservative, and includes stool softeners, analgesia, and possible local muscle relaxation; because of the risk of incontinence, surgical intervention is a last resort.



Primary (due to local trauma)

  • Location: 90% of all anal fissures located at the posterior commissure (6 o'clock in the lithotomy position)
  • Types of trauma:

Secondary (due to underlying disease)



  • Overdistension or disease of the anal mucosa laceration of the anoderm
    • Spasm of the exposed internal anal sphincter leads to pulling along the laceration, which impairs healing and worsens the extent of laceration with each bowel movement.
    • The resultant pain results in voluntary avoidance of defecation and constipation, which worsens distension of the anal mucosa.
  • The posterior commissure is believed to have a very poor blood supply, which predisposes it to ischemia (exacerbated by poor perfusion during increased anal pressure).


Clinical features

  • Sharp, severe pain during defecation
  • Rectal bleeding (often bright red and minimal; should not be confused with other types of bleeding such as in colorectal cancer or hemorrhoids)
  • Perianal pruritis
  • Chronic constipation (see “Pathophysiology” above)

The rule of anal fissure D's: Distally to the Dentate line; bleeDing During Defecation; Dull puDenDal pain; Diet low in fiber




Differential diagnoses


The differential diagnoses listed here are not exhaustive.




  • Persistent symptoms despite > 8 weeks of conservative therapy → endoscopy to exclude IBD
  • If IBD is excluded, then the patient should receive definitive surgical treatment.

Outpatient procedures


  • Indicated when conservative treatment is unsuccessful
  • The risk of fecal incontinence (e.g., high in multiparous or elderly patients) determines the type of surgical intervention.
    • Low risk
      • Sphincterotomy (e.g., lateral internal sphincterotomy)
      • Anal dilatation (although there is a high risk of fecal incontinence with this procedure)
    • High risk
      • Anal advancement flap
      • Fissurectomy (excision of the fissure)

Conservative therapy is preferred because of the risk of incontinence!