Anorectal Fistula and Pelvirectal Abscess

Abstract

The muscles of the pelvic floor assume the anatomical configuration of two cylinders, one within the other. The inner cylinder consists of the lower rectum and anal canal, which contains mucosa and submucosa as well as the circular and the longitudinal muscle layers. In the anal canal the circular muscle layer is very well developed and constitutes the internal sphincter muscle, an involuntary sphincter made up of smooth muscle. The outer cylinder consists of the external sphincter and the puborectalis muscles. At its proximal extremity the outer cylinder fans out in the shape of a funnel since it is continuous with the levator ani muscles that form the pelvic diaphragm. The inner visceral muscle cylinder and the outer somatic cylinder are separated by the intersphincteric space (Fig. 84–1). It is striking that in the course Anorectal Fistula and Pelvirectal Abscess of a low anterior resection, if the surgeon dissects the rectum down to the puborectalis level, it is possible to insert a finger or an instrument along the outer wall of the rectum all the way down to the perianal skin without dividing any structure. This passage takes place in the intersphincteric space external to the internal sphincter muscle and internal to the external sphincter. This fact is important in understanding the spread of infection and the formation of anal fistulas.