What is a typical feature of an anal fissure on examination?

In the examination of an anal fissure, a typical feature is a posterior midline epithelial defect. Anal fissures are linear tears in the anal mucosa, frequently located at the posterior midline due to the anatomy of the anal canal, particularly the blood supply which is less robust in this area compared to the anterior. This positioning is also related to the common nadir of tensile stress on the anal lining during defecation.

While fissures can occasionally occur in other locations, such as laterally, the most classical presentation is indeed the posterior midline defect. The anterior location is less common and typically associated with certain conditions such as inflammatory bowel disease or trauma.

The appearance of the fissure in the correct answer indicates a distinct linear defect, which sharply defines it from irregular tears or other forms of trauma to the anal area. This anatomical specificity helps in diagnosing an anal fissure during clinical examination and guides appropriate management.