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anal intraepithelial neoplasia

Tuesday 30 November 2010

AIN ; dysplasia of the squamous epithelium of the anus / perianal area; anal intra-epithelial neoplasia



- squamous epithelium in hemorrhoid sample : high grade anal intra-epithelial neoplasia.

The classification of anal intraepithelial neoplasia (AIN ) in mucosal biopsies is subject to considerable interobserver variability.

Ki-67 labeling detects anal HPV-related changes with a high degree of sensitivity and specificity, whereas increased p16/CDKN2A staining is strongly associated with high-grade squamous neoplasia. A combination of these markers may aid interpretation of anal mucosal biopsy samples. (20871219)


- low-grade anal intraepithelial neoplasia (LGAIN)
- high-grade anal intraepithelial neoplasia (HGAIN)

- Low grade squamous intraepithelial lesion (LGAIN)

  • AIN1 : Low grade dysplasia (the lower 1/3 of the epithelium); includes HPV change / condyloma
  • 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 (HGAIN)

  • The current preferred terminology, though often the clinicians will requests AIN 2 or 3 be specified in parenthesis
  • AIN2 : Used to be called indermediate grade; dysplasia reaches to the middle 1/3 of the epithelium
  • AIN3 : Dysplasia reaches to the upper 1/3 of the epithelium

Some people use this interchangeably with carcinoma in situ, others split them into 2 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

See also

- HPV-associated anal anomalies
- squamous intraepithelial neoplasia (SIN )

- anal epithelial dysplasia

Open references

- Anal cancer and intraepithelial neoplasia screening: A review. Leeds IL, Fang SH. World J Gastrointest Surg. 2016 Jan 27;8(1):41-51. doi : 10.4240/wjgs.v8.i1.41
PMID: 26843912

- Anal cancer and intraepithelial neoplasia: epidemiology, screening and prevention of a sexually transmitted disease. Medford RJ, Salit IE. CMAJ. 2015 Feb 3;187(2):111-5. doi : 10.1503/cmaj.140476 PMID: 25512647

- Current treatment options for management of anal intraepithelial neoplasia. 2013. doi : 10.2147/OTT.S38217


- P16/CDKN2A and Ki-67 enhance the detection of anal intraepithelial neoplasia and condyloma and correlate with human papillomavirus detection by polymerase chain reaction. Pirog EC, Quint KD, Yantiss RK. Am J Surg Pathol. 2010 Oct;34(10):1449-55. PMID: 20871219