1 General introduction 15 CAF is one of the most common proctological problems. In a study by Mapel,11 in patients in the United States, the overall annual incidence was 0.11% (1.1 cases per 1000 persons). In the Netherlands, the incidence is 0.25% (2.5 cases per 1000 persons), with the highest incidence (4.3 per 1000) in women between 25-44 years.12 Anatomy of the anorectum The rectum comprises the most distal end of the gastrointestinal tract. It is a hollow tube, 12 to 15 cm long, composed of a layer of longitudinal muscle woven with the underlying circular muscle.13 The anal canal is defined as the beginning of the dentate line and ending of the anal verge, forming a transitional zone between the epithelium and perianal skin.14 The length of the anal canal is approximately 4 cm.15 At the dentate line, the columns of Morgagni begin with anal crypts at the base. The inner layer of the anal canal is composed of the internal anal sphincter (IAS), the outer layer of the anal canal consists of the external anal sphincter (EAS) and puborectalis muscle. In between these layers there is a fat containing intersphincteric space with the conjoined longitudinal muscle.16 The IAS ends about 1 cm proximal to the distal edge of the EAS and is a smooth muscle sphincter, innervated by the sympathic fibers from the inferior pelvic plexus and the parasympathic nerve fibers (S2-S4).16 The IAS is the main contributor to the anal resting pressure and contributes up to 80% of the anal resting pressure (50-70mmHg). Other contributors to anal resting pressure include the anal mucosal folds, the anal vascular cushions, the EAS and puborectalis muscle.17
RkJQdWJsaXNoZXIy MTk4NDMw