Anal sphincter

Last revised by Dr Calum Worsley ◉ on 28 Oct 2021

Citation, DOI & article data

Citation:

Wong, A., Worsley, C. Anal sphincter. Reference article, Radiopaedia.org. (accessed on 04 Oct 2022) https://doi.org/10.53347/rID-33134

DOI:

https://doi.org/10.53347/rID-33134

Permalink:

https://radiopaedia.org/articles/33134

rID:

33134

Article created:

01 Jan 2015 by Dr Aaron Wong

Revisions:

12 times by 10 users - see full revision history

Systems:

Musculoskeletal, Gastrointestinal

Section:

Anatomy

Tag:

anus; sphincter; anatomy

Synonyms:

The anal sphincter is divided into internal and external anal sphincters. It surrounds the anal canal.

Composed of skeletal muscle and classically categorized into deep, superficial, and subcutaneous parts:

deep part
- circular muscle fibers
- blends with puborectalis part of levator ani (posteriorly and laterally)
- this region is called the anorectal ring and is palpable on rectal examination
superficial part
- elliptical muscle fibers
- attaches from the tip of the coccyx posteriorly to the perineal body anteriorly
- only part of the sphincter with bony attachment
subcutaneous part
- circular muscle fibers
- lower ends curve inwards, lying below the end of the internal sphincter
  - the intersphincteric groove that results is palpable on examination