Perianal sepsis

Anatomy of anal canal

  • Internal sphincter = smooth muscle
  • External sphincter = striated muscle
  • Mucosa of upper third of anal canal – no somatic sensation
  • Mucosa of lower tow thirds of anal canal- somatic innervation from inferior rectal nerves
  • Anal gland occur in intersphinteric plane & open at level of dentate line
Perianal anatomy

Perianal & ischiorectal abscess

  • Probably arise from intersphinteric sepsis (Cryptoglandular Hypothesis)
  • Abscesses classified as:
    • Perianal
    • Ischiorectal
    • Intersphinteric
    • Supralevator
  • Initial surgery should simply be incision and drainage
  • Avoid looking for fistula at initial surgery
  • Rectal EUA at approximately five days
  • Especially if gut related organisms on culture
  • 80% recurrent abscesses associated with a fistula

Fistula-in-Ano

  • Goodsall's Rule = An external opening situated behind the transverse anal line will open into the anal canal in the midline posteriorly. An anterior opening is usually associated with a radial tract
  • Fistulae may be classified as:
    • Intersphinteric (70%)
    • Transphinteric (25%)
    • Suprasphinteric (5%)
    • Extrasphinteric (<1%)
  • Extrasphinteric fistulae are usually not associated with intersphinteric sepsis
  • Consider inflammatory bowel disease or neoplasia

Perianal fistulae

Investigation

  • Clinical assessment
  • MRI
  • Ultrasound

Picture provided by Richard Brouwer, St Vincent's Hospital, Melbourne, Australia

Treatment

  • Puborectalis is the key to future continence
  • Low fistulas - Lay open with either fistulotomy or fistulectomy
  • High fistulas - Require two stage surgery
  • Setons - loose or tight
  • Anorectal advancement flap may be considered

Transphinteric fistula-in-ano

Picture provided by Kahlid Hameed, Aga Khan University Hospital, Karachi, Pakistan

Bibliography

Hughes F,  Mehta S.  Anorectal sepsis.  Hosp Med 2002;  63:  166-169

McCourtney J S, Finlay I G.  Setons in the surgical management of fistula-in-ano.  Br J Surg 1995; 82: 448 - 452.

Seow-Choen F,  Nicholls R J.  Anal Fistula.  Br J Surg 1992; 79: 197 - 205.

Thomas P.  Decision making in surgery; acute anorectal sepsis.  Br J Hosp Med 1993; 50: 204 - 205.

 

 
 

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