Sonographic, manometric, and myographic evaluation of the anal sphincters morphology and function

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A direct comparison of anal sphincter physiology (muscle performance and anatomy-muscle thickness) has not yet been undertaken but may be of importance in patients with defecation disorders.


We evaluated 15 healthy volunteers by means of anorectal manometry to determine pressure functions of the internal and external anal sphincter. Transcutaneous electromyography was recorded to assess the electrical activity of the external anal sphincter. Thickness of the anal sphincter muscles was measured sonographically from within the anal canal with dorsal projection using a 7.5-MHz 360° rectal panorama scanner.


It was shown that neither is the muscle thickness of the external anal sphincter during rest (6.26±1.02 mm) or during squeezing (7.40±1.39 mm) correlated to its squeeze pressure (138.8±15.2 mmHg), nor is the diameter of the internal anal sphincter (2.09±0.58 mm) correlated to its resting pressure (61.1±15.2 mmHg). Finally, the thicker the internal anal sphincter muscle, the lower the electrical activity of the external anal sphincter during squeezing (r=0.74, P<0.001).


It is concluded that both manometry to assess sphincter function and sonography to determine sphincter morphology are important measures in the evaluation of continence function.

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