The term Anal Intraepithelial Neoplasia (AIN) describes the microscopic finding of dysplastic, non-malignant cells in the anal canal. AIN has been subdivided into AIN I, II, and III, representing low, moderate, and high-grade dysplasia. This dysplasia has been thought to arise as a result of local infection with the Human papillomavirus. The Human papillomavirus is a small double-stranded DNA virus with a diameter of 55 nm. and is encased in a protein capsid. The term AIN has gradually replaced other descriptive terminology such as atypical squamous cells of indeterminate significance (ASCUS), low-grade squamous intraepithelial lesions (LSIL), or high-grade squamous intraepithelial lesions (HSIL).
Anal itching. Pruritus ani. At one time or another, everyone has experienced this unpleasant sensation. Most often, the delightful scratching of the itch relieves the discomfort and puts a stop to the maddening sensation. Not uncommonly however, the itch occurs at an inconvenient moment, in public, during an intimate social situation or at a time when scratching is not possible without looking a bit ridiculous. Worse, the itching may become chronic, with the need to scratch becoming a constant annoyance, bordering on pain.
Squamous cell carcinoma of the anus is the most well known member of an uncommon group of GI neoplasms. The incidence of this tumor has been increasing slowly, with 3,500 cases reported in the United States in 2001, and 5,260 cases reported in 2009.