Anal intraepithelial neoplasia

Anal intraepithelial neoplasia (AIN) is a histological diagnosis for dysplasia in the anal squamous epithelium. If the dysplasia is limited to the lower third of the dermis, it is classified as AIN 1° or low grade AIN (LGAIN); in cases of involvement of the middle and upper third it is called AIN 2 and 3° (high grade AIN/HGAIN). Infection with human papilloma virus (HPV) is generally the underlying cause. Untreated AIN may become invasive. Risk factors are, among others, smoking, immunosuppression, human immunodeficiency virus infection, a history of anogenital warts, intraepithelial neoplasia and HPV-associated cancer. AIN may present as clinically inconspicuous, but also as eczematous or papulous lesions. LGAIN or anogenital warts should be treated according to the guidelines. HGAIN can be treated using excisional, ablative, and topical treatment modalities. Because recurrence is frequent, follow-up of HGAIN is mandatory. © 2017, Springer Medizin Verlag GmbH, ein Teil von Springer Nature.