Three-Dimensional Endoanal Ultrasound Features of the Anal Sphincter in Asian Primigravidae

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The normal parameters of 3-dimensional endoanal ultrasound (3DEAUS) of the anal sphincter have not been reported for primigravidae or pregnant women at present. 3DEAUS parameters in Asian primigravidae were assessed in this study.


We analyzed 3DEAUS data of 101 consecutives Asian primigravidae, assessed in the early third trimester. The assessment was performed with a rigid ultrasonic probe (Olympus® RU 12M-R1 probe and EU-ME1 ultrasound system (Olympus Corp., Shinjuku, Japan). The Wilcoxon signed-rank test was used to detect the differences in pressure in different quadrants.


The participants had a mean age of 24.7 (standard deviation [SD], 5.1) years. The Cleveland Clinic Incontinence Score was normal in all participants. The anal sphincter complex had 3 characteristic segments that were identifiable: upper, middle and lower. The puborectalis muscle was identified as a striated “V”-shaped sling, and its mean thickness was 7.44 (SD, 1.41) mm. The mean thickness of internal (IAS) and external (EAS) sphincters at the mid-sphincter level were 1.78 (SD, 0.59) and 5.49 (SD, 1.21) mm, respectively. The EAS measured 6.02 (SD, 1.07) mm at the lower sphincter level. The statistically significant differences seen in the in quadrants were: the IAS was thicker anteriorly (Z = −2.642; P = .008), the EAS at both midsphincter level (Z = −3.70; P < .001) and lower sphincter level (Z = −7.712; P < .001) was thicker posteriorly, and the IAS was thicker at the 9 o'clock position (Z = −2.081; P = .037). Good symmetry at all 3 levels was seen in the EAS (including the puborectalis muscle).


Normal values of 3DEAUS for primigravidae have been identified and may serve as reference values for other laboratories.

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