Pelvic Floor/Anal Canal: Surgical Anatomy and Embryology

Abstract

The pelvic floor closes the caudal opening of the pelvic cavity and provides three different functions: (1) permanent support of pelvic organs; (2) controlled opening for micturition, defecation and parturition; and (3) competent closure of the anal canal and urethra to ensure faecal and urinary continence. For these purposes the pelvic floor comprises a pelvic and urogenital diaphragm in which the external anal and urethral sphincters are integrated. Due to its larger dimensions and less developed muscle strength and nerve supply, the female pelvic floor is more susceptible to both pelvic floor insufficiency and pelvic organ prolapse. The anal canal corresponds to the last segment of the gastrointestinal tract and passes through the tip of the funnel-shaped pelvic floor. Together with the pelvic floor muscles the different components of the anal canal—in particular the internal and external anal sphincters, the haemorrhoidal plexus and anoderm—provide the prerequisites for proper faecal continence and coordinated defaecation. Thus, one of the most desirable functional aims in colorectal surgery for both benign and malignant diseases is the preservation of these abilities. Detailed knowledge of the anatomy of the pelvic floor and the anal canal is fundamental to achieve these goals.