The rectum as measured by rigid proctoscopy extends approximately 15 cm in length from the anal verge. It occupies the pelvis and angulates at the level of the coccyx to pass through the levator plate. The rectum is posterior to the uterus, cervix, and posterior vaginal wall in women and the bladder, vas deferens, seminal vesicles, and prostate in men (Figure 1.1). The proximal limit of the rectum is controversial and for most surgeons is best defined by the pelvic inlet, which is defined by a line between the sacral promontory and the pubic symphysis. The critical endoscopically identified anatomic landmarks are the three convex curves that correspond to the folds or valves of Houston. The left-sided valves are found at 7 cm to 8 cm and 12 cm to 13 cm, respectively, and the right valve is found from 9 cm to 11 cm from the anal verge. The middle valve (Kohlrausch’s plica) corresponds to the anterior peritoneal reflection. Below this peritoneal reflection the rectum is entirely extraperitoneal and loses its serosal surface. The middle rectal valve’s relationship to the anterior peritoneal reflection makes it an important landmark in the pre-treatment assessment of a rectal cancer.
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