Endoanal ultrasonography in the staging of anal carcinoma
Histologically the mucosa of the anal canal can be divided into three zones (Fig. VII.1). The upper part is covered with colorectal type mucosa. The middle part is the anal transitional zone (ATZ), which is covered by a specialized epithelium with varying appearances; it extends from the dentate line and on average 0.5–1.0 cm upwards. The lower part extends from the dentate line and downwards to the anal verge and has formerly been called the pecten. It is covered by squamous epithelium, which may be partly keratinized, particularly in the case of mucosal prolapse. The perianal skin (the anal margin) is defined by the appearance of skin appendages.
KeywordsAnal Canal Anal Cancer Internal Anal Sphincter Dentate Line External Sphincter
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