The incidence of anal cancer in the general population is higher among women than men, and has been rising steadily since the 1970s. Although the incidence in the general population is relatively low, certain groups of women are at increased risk of anal cancer. These include women with a history of cervical or vulvar high-grade squamous intraepithelial lesions (HSIL) or cancer and women with immunocompromise due to HIV infection or other causes such as medication to prevent transplant rejection. As with algorithms designed to identify and treat cervical HSIL to prevent cervical cancer, anal cancer prevention programs include visual inspection of the at-risk areas. For anal cancer prevention this technique is known as high resolution anoscopy (HRA).
HRA includes the use of a colposcope to identify anal HSIL, identify areas to with biopsy to determine the grade of disease and ultimately guide targeted removal of lesions to reduce the risk of cancer.
Although there are many similarities between colposcopy and HRA, including the use of acetic acid and Lugol’s solution, there are also several differences. These include the need to maintain focus over a wider length of at-risk mucosa; the need to focus the colposcope through an internal plastic anoscope; the need to manipulate the anoscope and swabs/brushes to flatten folds and push aside other normal anatomic features such as hypertrophic papillae to properly visualize the entire mucosa; and the need to remove blood, mucus and stool. Other common and/or normal anatomic features may pose challenges to a complete HRA including anal crypts and hemorrhoids. In addition while acetic acid and Lugol’s solution have been validated to identify anal HSIL, patterns of vascular change and other signs of anal HSIL differ somewhat from those of the cervix. A complete HRA includes inspection of the entire squamocolumnar junction (SCJ), the area proximal to the SCJ, the mid-canal to the dentate line, the distal canal to the verge and the perianal keratinized skin to a radius of 5 cm from the anal opening. The appearance of anal lesions varies considerably throughout this wide range of epithelial surface. The performance of acetic acid and Lugol’s solution to identify anal HSIL varies as well, as do the challenges associated with identifying disease at these different locations.
HRA is an important tool to identify anal HSIL, biopsy it to confirm the grade of disease and to treat it to prevent progression to anal cancer. Gynecologists should consider learning and performing this techinque in women at increased risk for anal cancer.