Anus and perianal area
Inflammatory diseases
Crohn's disease

Author: Arvind Rishi, M.D. (see Authors page)
Editor: Toby Cornish, M.D.

Revised: 26 September 2017, last major update December 2013

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Crohn's disease [title] anus "loattrfree full text"[sb]

Cite this page: Rishi, A. Crohn's disease. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/anuscrohns.html. Accessed October 20th, 2017.
Definition / general
  • Anal canal involvement in 25 - 45% of Crohn's patients with small bowel involvement; up to 75% with colonic involvement
Terminology
  • Also called granulomatous colitis but this is less specific
Sites
  • Anal, anorectal and perianal skin
Etiology
  • Etiology of chronic inflammatory bowel disease is unknown - may involve combination of genetic and inflammatory risk factors
  • Genetic factors suggested by 10 - 15x increased risk in those with affected first degree relatives, 42 - 58% concordance rate in monozygotic twins
  • Environmental factors such as smoking, certain food antigens, NSAID use and infectious agents may be important
  • Perianal fistulas may develop from deep fissures or anal gland abscesses
Clinical features
  • Symptomatic perianal disease may precede GI symptoms in 5 - 20% of patients (Dis Colon Rectum 1996;39:136, Aust N Z J Surg 1996;66:5, Dis Colon Rectum 1995;38:121)
  • The presence of recurrent isolated anal fissures, fistulas or perianal abscesses should raise the suspicion for evolving Crohn's disease; internal fistulas are virtually pathognomic
  • Major complications include abscesses, fistulas, anal tags and fissures, which can present as anal pain, purulent discharge, fresh bleeding per rectum or anal incontinence (Am Fam Physician 2010;82:419)
  • Disease location and age < 40 years are most common factors associated with perianal complications (Inflamm Bowel Dis 2002;8:244)
  • Malignancy (anal canal adenocarcinoma) may be seen in longstanding perianal Crohn's disease (Intern Med 2013;52:445)
  • Perianal fistulizing disease is associated with genetic susceptibility involving chromosome 5 with candidate interleukin genes IL3, IL4, IL5, I-13, CSF2 (World J Gastroenterol 2011;17:1939)
Laboratory
  • Serum pANCA may be increased in patients with left sided disease with an ulcerative colitis-like clinical phenotype and histological features
Case reports
Clinical images

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Large perianal skin tags

Gross description
  • Varies based on location of fistula and associated healing process
    • May have firm and fibrotic perirectal areas with adherent perianal skin showing external communication of fistula
    • May present as perirectal mass if there has been significant healing

  • Some grossing points:
    • Recommended to take gross photographs of specimen when fresh
    • Communication of fistula is best demonstrated by inserting a blunt metallic probe from the mucosal aspect of unfixed resection specimen - the key is finding the opening of either the sinus or fistula tract at the mucosal aspect
    • Formalin fixation of these specimens is best accomplished by opening the luminal aspect of colon in a longitudinal direction and pinning the specimen flat
    • This technique may be challenging for large resection specimens with long lengths of colon
    • Adhesions or fistulae to other visceral organs or parts of the bowel may also be present, distorting the specimen and making orientation difficult
Gross images

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Colon (case 133)

Microscopic (histologic) description
  • Features of acute colitis: cryptitis (neutrophils in crypt epithelium), crypst abscesses (neutrophils within crypt lumens), erosions, ulcers
  • Features of chronic colitis: crypt distortion, loss of goblet cells, basal plasmacytosis, crypt shortfall (base of crypts not touching the muscularis mucosae), Paneth cell metaplasia in left colon
  • Nonnecrotizing granulomatous inflammation with variable giant cells in mucosa or fibroconnective tissue of fistula tract (may resemble foreign body type granulomas)
  • Transmural chronic inflammation (best visualized on resection specimens)
  • Patchy mucosal involvement with skip lesions which looks near normal on histology or may have mild reactive epithelial changes
  • Acute and chronic inflammatory granulation tissue secondary to ulceration and fistula formation
Microscopic (histologic) images

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Epithelioid cells, giant cells, lymphocytes

Fistula formation

Fistula opening onto perineum

Differential diagnosis