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Anal intraepithelial neoplasia

Last edited: 4/14/2026

Overview

Anal intraepithelial neoplasia (AIN) refers to precancerous lesions of the anal epithelium, often associated with human papillomavirus (HPV) infection, and represents a spectrum of dysplastic changes that can progress to anal squamous cell carcinoma if left untreated 717.

Diagnosis

  • Key Diagnostic Criteria: Identification through high-resolution anoscopy with biopsy confirmation 7.
  • Recommended Tests: Anal cytology screening, particularly in high-risk populations such as HIV-positive individuals and men who have sex with men 7.
  • Grading: Classified using the Lower Anogenital Squamous Terminology (LA-ST) system, which includes low-grade and high-grade lesions 15.
  • Management

  • First-Line Treatment: Loop Electrosurgical Excision Procedure (LEEP) for high-grade lesions (AIN 2/3) to reduce progression risk 4.
  • Adjunctive Treatments: Topical therapies such as 5-fluorouracil or imiquimod may be considered for lower-grade lesions 17.
  • Surveillance: Regular follow-up with cytology and high-resolution anoscopy to monitor for recurrence or progression 7.
  • Special Populations

  • HIV-Infected Individuals: Higher prevalence and more aggressive management required due to increased risk of progression 3.
  • Men Who Have Sex With Men: Higher risk group necessitating targeted screening programs 7.
  • Key Recommendations

  • Screen High-Risk Populations Regularly: Implement routine screening programs for anal cytology in HIV-positive individuals and men who have sex with men to detect AIN early (Evidence: Moderate 73).
  • LEEP for High-Grade Lesions: Use LEEP as the primary treatment modality for AIN 2/3 to significantly reduce the risk of progression to invasive cancer (Evidence: Expert opinion 4).
  • Post-Treatment Surveillance: Schedule frequent follow-up visits with cytology and high-resolution anoscopy to monitor for recurrence or new lesions (Evidence: Moderate 7).
  • References

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MedEdPORTAL : the journal of teaching and learning resources 2023. link 5 Ikeda M, Mikami M, Yasaka M, Enomoto T, Kobayashi Y, Nagase S et al.. Association of menopause, aging and treatment procedures with positive margins after therapeutic cervical conization for CIN 3: a retrospective study of 8,856 patients by the Japan Society of Obstetrics and Gynecology. Journal of gynecologic oncology 2021. link 6 Cho HW, Kim SY, Lee YJ, Ouh YT, Min KJ, Lee SH et al.. Doctor and patient awareness of treatment options for cervical intraepithelial neoplasia 1 (CIN 1): a survey questionnaire approach. Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology 2020. link 7 Revollo B, Videla S, Parés D. Anal intraepitelial neoplasia: how and for who do we perform a screening program?. Revista espanola de enfermedades digestivas 2018. link 8 Culp WTN. Interventional Radiology Management of Nonresectable Neoplasia. The Veterinary clinics of North America. Small animal practice 2018. link 9 Doo DW, Stickrath EH, Mazzoni SE, Alston MJ. Lack of Agreement Between Endocervical Brush and Endocervical Curettage in Women Undergoing Repeat Endocervical Sampling. Journal of lower genital tract disease 2016. link 10 Stoler MH, Ronnett BM, Joste NE, Hunt WC, Cuzick J, Wheeler CM. The Interpretive Variability of Cervical Biopsies and Its Relationship to HPV Status. The American journal of surgical pathology 2015. link 11 Park CH, Min JH, Yoo YC, Kim H, Joh DH, Jo JH et al.. Sedation methods can determine performance of endoscopic submucosal dissection in patients with gastric neoplasia. Surgical endoscopy 2013. link 12 Gage JC, Schiffman M, Hunt WC, Joste N, Ghosh A, Wentzensen N et al.. Cervical histopathology variability among laboratories: a population-based statewide investigation. American journal of clinical pathology 2013. link 13 Gage JC, Joste N, Ronnett BM, Stoler M, Hunt WC, Schiffman M et al.. A comparison of cervical histopathology variability using whole slide digitized images versus glass slides: experience with a statewide registry. Human pathology 2013. link 14 van den Einden LC, de Hullu JA, Massuger LF, Grefte JM, Bult P, Wiersma A et al.. Interobserver variability and the effect of education in the histopathological diagnosis of differentiated vulvar intraepithelial neoplasia. Modern pathology : an official journal of the United States and Canadian Academy of Pathology, Inc 2013. link 15 Darragh TM, Colgan TJ, Thomas Cox J, Heller DS, Henry MR, Luff RD et al.. The Lower Anogenital Squamous Terminology Standardization project for HPV-associated lesions: background and consensus recommendations from the College of American Pathologists and the American Society for Colposcopy and Cervical Pathology. International journal of gynecological pathology : official journal of the International Society of Gynecological Pathologists 2013. link 16 Schumacher B, Charton JP, Nordmann T, Vieth M, Enderle M, Neuhaus H. Endoscopic submucosal dissection of early gastric neoplasia with a water jet-assisted knife: a Western, single-center experience. Gastrointestinal endoscopy 2012. link 17 Dindo D, Nocito A, Schettle M, Clavien PA, Hahnloser D. What should we do about anal condyloma and anal intraepithelial neoplasia? Results of a survey. Colorectal disease : the official journal of the Association of Coloproctology of Great Britain and Ireland 2011. link 18 Kim JM, Cho MY, Sohn JH, Kang DY, Park CK, Kim WH et al.. Diagnosis of gastric epithelial neoplasia: Dilemma for Korean pathologists. World journal of gastroenterology 2011. link 19 Heresbach D, Kornhauser R, Seyrig JA, Coumaros D, Claviere C, Bury A et al.. A national survey of endoscopic mucosal resection for superficial gastrointestinal neoplasia. Endoscopy 2010. link 20 Chhieng DC, Bakdounes K, Connolly M, Gallaspy S, Roberson J, Eltoum I. HPV detection rate in discordant Pap tests between cytotechnologists and pathologists. Diagnostic cytopathology 2009. link 21 Alsharif M, Kjeldahl K, Curran C, Miller S, Gulbahce HE, Pambuccian SE. Clinical significance of the diagnosis of low-grade squamous intraepithelial lesion, cannot exclude high-grade squamous intraepithelial lesion. Cancer 2009. link 22 Edell ES. High-grade lesion: What does it tell us?. Thorax 2007. link 23 Tworek JA, Jones BA, Raab S, Clary KM, Walsh MK. The value of monitoring human papillomavirus DNA results for Papanicolaou tests diagnosed as atypical squamous cells of undetermined significance: a College of American Pathologists Q-Probes study of 68 institutions. Archives of pathology & laboratory medicine 2007. link 24 Lee CY, Ng WK. A follow-up study of atypical squamous cells in gynecologic cytology using conventional papanicolaou smears and liquid-based preparations: the impact of the Bethesda System 2001. American journal of clinical pathology 2007. link 25 Cai B, Ronnett BM, Stoler M, Ferenczy A, Kurman RJ, Sadow D et al.. Longitudinal evaluation of interobserver and intraobserver agreement of cervical intraepithelial neoplasia diagnosis among an experienced panel of gynecologic pathologists. The American journal of surgical pathology 2007. link 26 Baum ME, Rader JS, Gibb RK, McAlister RP, Powell MA, Mutch DG et al.. Colposcopic accuracy of obstetrics and gynecology residents. Gynecologic oncology 2006. link 27 Young NA, Moriarty AT, Walsh MK, Wang E, Wilbur DC. The potential for failure in gynecologic regulatory proficiency testing with current slide validation criteria: results from the College of American Pathologists Interlaboratory Comparison in Gynecologic Cytology Program. Archives of pathology & laboratory medicine 2006. link 28 Renshaw AA, Mody DR, Styer P, Schwartz M, Ducatman B, Colgan TJ. Papanicolaou tests with mixed high-grade and low-grade squamous intraepithelial lesion features: distinct performance in the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytopathology. Archives of pathology & laboratory medicine 2006. link 29 Renshaw AA, Prey MU, Hodes L, Weisson M, Haja J, Moriarty AT. Cytologic features of high-grade squamous intraepithelial lesion in conventional slides: what is the difference between cases that perform well and those that perform poorly?. Archives of pathology & laboratory medicine 2005. link 30 Renshaw AA, Dubray-Benstein B, Haja J, Hughes JH. Cytologic features of low-grade squamous intraepithelial lesion in thinprep papanicolaou test slides and conventional smears: comparison of cases that performed poorly with those that performed well in the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytology. Archives of pathology & laboratory medicine 2005. link 31 Bashir O, FitzGerald AJ, Goodlad RA. Both suboptimal and elevated vitamin intake increase intestinal neoplasia and alter crypt fission in the ApcMin/+ mouse. Carcinogenesis 2004. link 32 Tiersma ES, Peters AA, Mooij HA, Fleuren GJ. Visualising scanning patterns of pathologists in the grading of cervical intraepithelial neoplasia. Journal of clinical pathology 2003. link 33 Parker MF, Zahn CM, Vogel KM, Olsen CH, Miyazawa K, O'Connor DM. Discrepancy in the interpretation of cervical histology by gynecologic pathologists. Obstetrics and gynecology 2002. link02058-6) 34 Stoler MH, Schiffman M. Interobserver reproducibility of cervical cytologic and histologic interpretations: realistic estimates from the ASCUS-LSIL Triage Study. JAMA 2001. link 35 Hanson IM, Armstrong GR. Anal intraepithelial neoplasia in an inflammatory cloacogenic polyp. Journal of clinical pathology 1999. link 36 Díaz-Rosario LA, Kabawat SE. Performance of a fluid-based, thin-layer papanicolaou smear method in the clinical setting of an independent laboratory and an outpatient screening population in New England. Archives of pathology & laboratory medicine 1999. link 37 Vassilakos P, Saurel J, Rondez R. Direct-to-vial use of the AutoCyte PREP liquid-based preparation for cervical-vaginal specimens in three European laboratories. Acta cytologica 1999. link 38 Fowler BM, Giuliano AR, Piyathilake C, Nour M, Hatch K. Hypomethylation in cervical tissue: is there a correlation with folate status?. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 1998. link 39 Renshaw AA, Granter SR. Appropriate follow-up interval for biopsy confirmation of squamous intraepithelial lesions diagnosed by cervical smear cytology. American journal of clinical pathology 1997. link 40 Tabbara SO, Sidawy MK. Evaluation of the 5-year review of negative cervical smears in patients with high grade squamous intraepithelial lesions. Diagnostic cytopathology 1996. link1097-0339(199607)15:1<7::AID-DC3>3.0.CO;2-H) 41 Bolin TD, Hunt RH, Korman MG, Lambert JR, Lee A, Talley NJ. Helicobacter pylori and gastric neoplasia: evolving concepts. The Medical journal of Australia 1995. link 42 Brotzman GL, Mark DH, Wolkomir MS. Influences on teaching colposcopy and treatment modalities in family practice programs. Family medicine 1995. link 43 Markos AR, Wade AA, Walzman M. Management of cervical intraepithelial neoplasia in departments of genitourinary medicine--a national survey. International journal of STD & AIDS 1993. link 44 Gordon P, Hatch K. Survey of colposcopy practices by obstetrician/gynecologists. The Journal of reproductive medicine 1992. link 45 Kumar K, Hodgins M. Use of interactive videodisc for teaching of pathology laboratory cases. The Journal of pathology 1990. link 46 Willman CL, Stewart CC. General principles of multiparameter flow cytometric analysis: applications of flow cytometry in the diagnostic pathology laboratory. Seminars in diagnostic pathology 1989. link 47 Ismail SM, Colclough AB, Dinnen JS, Eakins D, Evans DM, Gradwell E et al.. Observer variation in histopathological diagnosis and grading of cervical intraepithelial neoplasia. BMJ (Clinical research ed.) 1989. link 48 Maddox PH, Tay SK, Jenkins D. A new fixed cryosection technique for the simultaneous immunocytochemical demonstration of T6 and S100 antigens. The Histochemical journal 1987. link 49 Sterrett GF, Alessandri LM, Pixley E, Kulski JK. Assessment of precancerous lesions of the uterine cervix for evidence of human papillomavirus infection: a histological and immunohistochemical study. Pathology 1987. link 50 Sprinkle PM, Veltri RW. Epstein-Barr virus infection and neoplasia. Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery 1981. link

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