Anal Intraepithelial Neoplasia
Anal intraepithelial neoplasia, a premalignant condition, is a difficult problem of the anal canal and margin. The disorder most commonly causes no discernible symptoms; yet patient concern and treatment uncertainties render anal intraepithelial neoplasia
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Key Concepts • Anal intraepithelial neoplasia is a dysplastic condition of squamous tissue and is considered to be a premalignant stage of anal cancer. • The histological findings and cellular abnormalities mirror cervical dysplasia. • Anal cytology is a useful method to identify anal neoplasia in high-risk groups. • When cytology is concerning, the evaluation of anal neoplasia can proceed with anal cytology and high-resolution microscopy, a technique similar to colposcopy. • A targeted approach to dysplasia ablation through microscopy is more sparing than historically practiced wide local excisions and flap advancements. • Treatment should be tailored to the patient’s degree of dysplasia, risk factors, immune status, continence, symptoms, and likelihood of progression.
Introduction Anal intraepithelial neoplasia is a dysplastic condition of the squamous tissue and is considered to be a premalignant stage of anal cancer. Anal intraepithelial neoplasia (AIN) is further stratified into three grades: AIN I, AIN II, and AIN III, defined as low-, moderate-, and high-grade dysplasia, respectively (Figure 20-1). The histological findings, including the cytologic changes, mitotic activity, nuclear membrane changes, and cellular abnormalities [1, 2], mirror cervical dysplasia grading. Terminology can be confusing as anal intraepithelial neoplasia is referred to by many names including anal dysplasia, intraepithelial carcinoma, intramucosal carcinoma, squamous cell carcinoma in situ, and Bowen’s disease. In addition, recently the terms high-grade anal intraepithelial neoplasia (HGAIN) and low-grade anal intraepithelial neoplasia (LGAIN) have been proposed that correspond to AIN III/II and AIN I, respectively [1].
In this chapter we will use the terms anal intraepithelial neoplasia which parallel the pathophysiology of cervical intraepithelial neoplasia, vulvar intraepithelial neoplasia, and perineal intraepithelial neoplasia.
Symptoms The vast majority of individuals will experience no outward manifestation of human papillomavirus (HPV) infection, and similarly most patients with AIN have no clear symptoms. A small subset of patients will describe occasional rectal bleeding, and an even smaller group will experience pain with bowel movements. As AIN progresses to anal cancer, symptoms become more frequently reported. In fact, 50 % of patients with invasive cancer describe pain and bleeding [3, 4]. A minority of patients with anal intraepithelial neoplasia describe a palpable lesion on the non-hair-bearing portion of the anal skin, but the majority have no outward sign of disease. However, those patients with signs of external genital warts and immunosuppression have a very high risk of AIN.
Epidemiology Anal intraepithelial neoplasia develops from HPV contact generally through direct exposure [1, 5, 6]. It is estimated that there are more than 100 subtypes of HPV but not all have been implicated as disease causing. In fact, as stated in the prior section, most patients who come into contact with HPV have no actual symptoms an
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