Anorectal Diseases

Published on 16/04/2015 by admin

Filed under Surgery

Last modified 16/04/2015

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16 Anorectal Diseases

Anorectal Anatomy

General Anorectal Anatomy

Rectum

• Wider diameter than most of colon, except for cecum

• 12-16 cm in length, starting at about the sacral promontory, extending to dentate line of anal canal

• Anterior aspect of upper 4-6 cm is intraperitoneal, with serosal surface.

• Lower (majority of) rectum lies within extraperitoneal pelvis, with no serosa.

• Taeniae coli spread out at rectosigmoid junction to form a continuous, external longitudinal muscle layer.

• Three flexures of rectum usually correspond with 3 transverse rectal folds (superior, middle, and inferior rectal valves).

• Valves overlie thickenings of circular muscle.

• Ampulla: terminal portion rectum below inferior valve, supported by levator ani and anococcygeal ligament

• Women: thin rectovaginal septum separates anterior inferior rectum from vagina

• Men: prostate and seminal vesicles lie anterior to inferior rectum

• Mucosa: columnar epithelium, down to dentate line

Anal Canal

• 3-5 cm in length, from level of levator ani muscles to anal verge

• Canal includes dentate line, anal glands, internal and external sphincter muscles, and hemorrhoidal vessels.

• External anal sphincter muscles: striated muscle, with somatic innervation under voluntary control

• Internal anal sphincter muscle: continuation of inner, circular smooth muscle of hindgut, with autonomic (involuntary) innervation

• Stratified squamous epithelium lines anal canal, beginning at dentate line.

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