A Study into External Rectal Anatomy: Improving Patient Selection for Radiotherapy for Rectal Cancer

PURPOSE: This study was designed to determine the distance from the anal verge to the anterior peritoneal reflection in vivo, thereby improving the selection of patients for preoperative radiotherapy. METHODS: Measurement of the distance from the anal verge to the anterior peritoneal reflection, confluence of the taenia, and the origin of the sigmoid mesentery in 50 patients in the lithotomy position. RESULTS: The mean distance from the anal verge to the anterior peritoneal reflection was 11.9 cm (men) and 10 cm (women). To the origin of the sigmoid mesentery, the measurements were 18.8 cm (men) and 19.1 cm (women) and to the confluence of the taenia coli, 20.3 cm (men) and 18.8 cm (women). CONCLUSIONS: The distance from the anal verge to the origin of the sigmoid mesentery was approximately 19 cm in both men and women. Below this level tumors have limited mobility and should be amenable to radiotherapy.