Anus and perianal area
Premalignant lesions
Dysplasia

Author: Nicole Riddle, M.D. (see Authors page)

Revised: 11 October 2017, last major update September 2014

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

PubMed Search: Dysplasia [title] anus "loattrfree full text"[sb]

Cite this page: Riddle, N. Dysplasia. PathologyOutlines.com website. http://pathologyoutlines.com/topic/anusdysplasia.html. Accessed December 17th, 2017.
Definition / general
  • Topic discusses dysplasia of the squamous epithelium of the anus / perianal area
  • Dysplasia is defined similarly to the cervix, as increased nuclear size with hyperchromasia and irregular nuclear borders
  • Low grade squamous intraepithelial lesion:
    • AIN 1: Low grade dysplasia (the lower 1/3 of the epithelium); includes HPV change / condyloma
    • Note: Some people separate out pure HPV change from AIN I based on if there is any dysplasia at all or just HPV change; however convention dictates they both qualify for LGSIL
  • High grade squamous intraepithelial lesion:
    • The current preferred terminology though often the clinicians will requests AIN 2 or AIN 3 be specified in parenthesis
    • AIN 2: Used to be called indermediate grade; dysplasia reaches to the middle 1/3 of the epithelium
    • AIN 3: Dysplasia reaches to the upper 1/3 of the epithelium
      • Some people use this interchangeably with carcinoma in situ, others split them into two groups based on if there is any maturation or "does the top look like the bottom"
      • Note: There is some support for calling this lesion high grade squamous intraepithelial lesion (AIN 3) instead of carcinoma in situ for insurance purposes
Terminology
  • Also called anal intraepithelial neoplasia (AIN), carcinoma in situ (if high grade, AIN 3)
Epidemiology
Sites
  • Occurs in perianal skin or anal canal in flat mucosa or with condyloma acuminatum
Pathophysiology
  • Related to HPV, similar to the cervix
Diagrams / tables

Images hosted on other servers:

Schematic representation of SIL

Clinical features
  • May be incidental finding in hemorrhoid specimen
  • Often multicentric
Diagnosis
Treatment
  • If incidental finding in hemorrhoid specimen, excision is usually curative even for high grade AIN / ACIN (Hum Pathol 1991;22:528)
Microscopic (histologic) description
  • Defined similarly to cervix: increased nuclear size with hyperchromasia and irregular nuclear borders
  • Level of dysplasia defines low grade (AIN 1) or high grade (AIN 2 - 3)
Microscopic (histologic) images

Images hosted on other servers:

Cervix

Cytology description
  • Similar to cervical pap smears, same criteria
  • LSIL: koilocytes, nuclear enlargement 3x normal size
  • HSIL: increased nuclear cytoplasmic ratio, nuclear hyperchromasia and irregularity
Cytology images

Images hosted on other servers:

LSIL

Various images (fig. 30-35)

Positive stains
  • Similar to cervix
  • p16: should be diffuse block staining to call positive (a common mistake among pathologists is to call positive if only focal p16 staining)
  • Ki67: staining of cells above the basement membrane