Surgical Anatomy of Anal Canal and Rectum
Rectum is a fixed terminal portion of the large intestine that serves as a reservoir. It is about 10–14 cm in length, and it is located between the sigmoid colon above and the anal canal below. It begins at the level of S3 vertebra and ends by becoming continuous with the anus which corresponds to the apex of the prostate or lower end of the vagina and is 2–3 cm in front of and a little below the tip of the coccyx. The proximal part of the rectum joins the sigmoid colon at the rectosigmoid junction which is at about 15 cm from the anal verge, and the distal part joins the anal canal at the anorectal junction. The cardinal features of large intestine like the taenia, appendices epiploicae, sacculations, and well-defined mesentery are absent in the rectum (Corman 2005; Chapuis et al. 2002). The lower part of the rectum is dilated and is called rectal ampulla. Though the word rectum means straight, the rectum is not straight. It is curved both anteroposteriorly and from side to side. The lateral curves are three in number. The upper and the lower lateral curves are convex to the right. The middle lateral curve is convex to the left. Endoluminally, these folds are known as valves of Houston. The clinical significance of these folds is that they must be successfully negotiated during successful proctosigmoidoscopic examination (Corman 2005; Nivatvongs and Gordon 1992; Neugut and Pita 1988), and it is safer to take biopsies from these folds which are easily accessible and have no muscle. There is also minimal risk of perforation at these folds.
KeywordsAnal Canal External Anal Sphincter Dentate Line External Sphincter Internal Sphincter
- Corman ML. Colon and rectal surgery. 5th ed. Baltimore: Lippincott Williams & Wilkins; 2005. p. 1.Google Scholar
- Ellis H. Clinical anatomy. 10th ed. Hong Kong: Blackwell Science; 2002. p. 87–8.Google Scholar
- Marcio J, Jorge N, Habr Gamma A, et al. Anatomy and embryology of the colon, rectum and anus. In: Beck DE, editor. The ASCRS manual of colon and rectal surgery. New York: Springer; 2009.Google Scholar
- Nivatvongs S, Gordon PH. Surgical anatomy. In: Gordon PH, Nivatvongs S, editors. Principle and practice of surgery for Colon, Rectum and anus. St Louis: Quality Medical Publishing; 1992. p. 3.Google Scholar