Fistulas occur when there is an abnormal connection between two epithelialized surfaces that do not usually connect. Fistula-in-ano refers to a fistula between the skin and the anus. In 30 B.C., writings by Celsus advocated using a knife for treating fistula-in-ano. In cases where there were multiple openings, Celsus advocated for surgery in combination with ligature. John of Arderne (1307 – 1390 A.D.) described an operation for fistula-in-ano similar to treatments used today. 


  • Anorectal abscess
  • Cryptoglandular: anal crypts become blocked by inspissated debris/stool, infection develops at the anal glands which extends through the pathway of least resistance, abscess is formed in intersphincteric space leading to fistula development
  • Postoperative or traumatic
  • IBD
  • Anal fissure
  • Tuberculosis-related
  • Risk factors: obesity, diabetes, smoking, hyperlipidemia, sedentary lifestyle


  • Results from persistent communication between the anal canal (internal opening) and perianal skin (external opening) following spontaneous or surgical drainage


  • Cyclical pattern of pain and swelling
  • Drainage of the area associated with relief of symptoms
  • Fecal soiling
  • ± Bleeding

Physical Exam

  • ≥ 1 external opening with or without granulation tissue
  • Multiple external openings (“watering can perineum”) → suspicious for perianal Crohn disease
  • External opening on the anal margin skin with heaped-up granulation tissue tender to palpation
  • Digital rectal exam: palpation of a cord-like subcutaneous structure
  • Location of the fistula can help diagnose the type of fistula. Goodsall’s rule can be used to help locate the internal opening as well.
    • Submucosal: external opening in posterior midline close to anal verge
    • Intersphincteric: external opening off the midline close to anal verge
    • Low transsphincteric: external opening in anterior location
    • Transsphincteric or suprasphincteric: external opening in ischiorectal fossa
  • Draining of fistula tract


  • Anoscopy
    • Direct inspection of dentate line
    • May reveal an erythematous crypt or visible internal opening
    • Can help exclude inflammatory conditions
  • Exam under anesthesia
  • Routine imaging is not usually necessary. It may be considered in patients with recurrent or complex anal fistula, immunosuppression, or anorectal Crohn disease.
  • MRI pelvis
    • Identify primary and secondary openings
    • Delineate anatomy of fistula tracks
  • Endoanal US (EAUS)
  • Transperineal US (TPUS)


  • Goals for treatment
    • Eliminate sepsis
    • Remove or ablate epithelialized tracts
    • Avoid or minimize the risk of fecal incontinence
    • Prevent recurrence 
  • Lay-open technique (fistulotomy)
    • Indications: simple fistula-in-ano with normal anal sphincter function
    • Recurrence and incontinence are most significant complication
    • Risk factors for postoperative anal sphincter dysfunction: preoperative fecal incontinence, recurrent fistula, female sex, complex fistulas, previous anorectal surgery, women with anterior fistulas or who have occult sphincter damage from previous birthing trauma
  • Seton
    • Indications
      • Greater than lower ¼ of external anal sphincter involved (for first procedure) followed by either LIFT or anorectal advancement flap
      • When lay open technique is not possible or not advisable
      • Complex cryptoglandular anal fistulas
    • Used to control the fistula: narrow the fistula tract and prevent recurrent cyclical symptoms, shorten fistula track
  • Endorectal advancement flap (ERAF)
    • Indications
      • High transsphincteric fistulas
      • Suprasphincteric fistulas
    • Involves curettage of fistula tract, sutured closure of internal opening, and covering of the internal opening with a mobilized segment of the rectum
  • Ligation of intersphincteric fistula (LIFT)
    • Indications
      • Simple fistulas
      • Complex fistulas
      • Transsphincteric fistulas
    • Identification of internal opening with suture ligation of intersphincteric portion of the fistula. Tract and gland are excised and the wound is debrided. 
  • Fibrin glue → relatively ineffective
  • Anal fistula plug → relatively ineffective

Relevant Information

  • Goodsall’s rule: predict the course of the fistula tract and location of the internal opening;  help locate internal opening
    • Fistulas with an external opening anterior to the anus connect with anus/rectum in a straight line
    • Fistulas with an external opening posterior to the anus go toward a midline internal opening in the anus/rectum in a curvilinear fashion
  • Anal canal
    • Connection between the anal verge and anorectal junction; 2 – 4 cm in length
    • Dentate line lies midpoint in the anal canal
      • Proximal: longitudinal folds of columnar epithelium (columns of Morgagni)
      • Distal: smooth squamous epithelium (anoderm)
    • Anal crypts are located between the columns of Morgagni, where anal ducts empty


  • Simple vs. complex
    • Simple fistula
      • Due to glandular obstruction resulting in anorectal abscess, and ultimately, a fistula
      • Single tract, subcutaneous tract, involve < 30% of the external sphincter
    • Complex fistula
      • Any fistula that is high transsphincteric or when a fistulotomy would result in incontinence
      • Includes suprasphincteric, extrasphincteric, all anterior transsphincteric fistulas in women, fistulas caused by Crohn disease, malignancy, surgery, and trauma

Differential Diagnoses