The anal transitional zone (ATZ) is a strip of anal epithelium between the uninterrupted stratified squamous mucosa of the anal canal below and the uninterrupted columnar epithelium of the rectum above [1]. It is generally thought that the ATZ begins at the dentate line and extends upward toward the rectum for 1 to 2 cm, but this concept has been shaped by the simplistic drawings of the anus that appear in various textbooks and manuscripts. More recently, the ATZ has been found to be more irregular and shorter than was thought.