J Korean Soc Coloproctol.  1998 Jun;14(2):217-224.

Anal Endosonographic Findings of Internal Anal Sphincter in Normal Adult Korean


PURPOSE: To describe the appearance and average thickness of the internal anal sphincter with anal endosonography in healthy Korean adults. MATERIAL AND METHODS: 184 subjects(male: 96, female: 88) with no history of anorectal disease or surgery were studied with anal endosonography. The average thickness of internal sphincter was meas ured at the mid-anal canal. For the internal sphincter, which is often asymmetric, the thickness of each 4 part(12, 3, 6 and 9 o'clock direction) were measured in left lateral decubitus position.
The anal wall was well visualized in 5 layers(mucosa, submucosa, internal anal sphincter, intersphincteric plane, external anal sphincter) with anal endosonography. The anal endosonogram showed the internal anal sphincter as a homogenous, well-defined, hypoechoic, circular band, and slightly asymmetric. The average thickness of the internal anal sphincter in the area of mid-anal portion was 2.0 0.3 mm(range: 1~3 mm). There was no sexual difference; however, a significant positive correlation with age was found in average thickness of the internal anal sphincter. The correlation with lean body mass was not found.
The internal anal sphincter is well-visualized, best defined structure by anal endosonography. Average thickeness of the sphincter in Korean appeared to be the same as in the Western.


Internal anal sphincter; Anal endosonography

MeSH Terms

Anal Canal*
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