中文摘要：

目的采用CT排便造影显示肛门外括约肌（EAS）的形态及变化,评价其功能。方法分静息、缩肛、排便3期采集60名健康志愿者的坐位CT排便造影图像,重建标准的肛管冠状位及正中矢状位图像,对耻骨直肠肌（Pr）和EAS进行形态学测量。结果 Pr、EAS的深部和浅部分别在肛门直肠结合部、肛管上部和中下部水平压缩肛管,EAS皮下部位于肛管下方,内翻呈圆锥状,与肛周皮肤共同自下而上封堵肛管。静息期,EAS深部间距（31.50±4.10）mm,浅部间距（28.36±4.14）mm,肛管-EAS皮下部夹角（60.95±19.20）°;缩肛期,EAS作向心运动,更紧地闭合肛管,深部间距（30.85±4.10）mm,浅部间距（26.04±3.48）mm,皮下部内翻程度加大,肛管-EAS皮下部夹角（56.87±16.18）°;排便期,EAS作离心运动,肛管开放,深部间距（37.51±5.17）mm;浅部间距（31.68±5.10）mm,皮下部自内上向外下翻转,肛管-EAS皮下部夹角（112.23±22.48）°。结论 EAS主要通过压缩、悬吊、绞索和套塞方式维持肛门自制。EAS的深部、浅部和皮下部在排便时依次开放,其皮下部作翻转运动参与排便。

英文摘要：

Objective To show the morphology and morphologic changes of the external anal sphincter（EAS） with CT defecography,and to assess its function.Methods CT defecography was performed in 60 healthy volunteers in a sitting position.Coronal scans of the pelvis were obtained during the three standard phases of resting,squeezing and defecation,the multiplanar reconstruction images included the standard anal-coronal and mid-sagittal planes.Morphometric measurements were noted for the puborectalis（Pr） and the EAS.Results The Pr,the deep and superficial portion of the EAS squeezed the anal canal at the anorectal junction,upper-anal canal,middle and lower-anal canal levels,respectively.The subcutaneous part of EAS located below the anal canal and varus like a conus,which sealed with the perianal skin.At resting stage,the distance of the bilateral deep sphincter was（31.50±4.10）mm,the superficial sphincter was（28.36±4.14）mm.The anal-subcutaneous part angle was（60.95±19.20）°.During squeezing stage,the EAS did the centripetal movement to squeeze the anal canal more tightly,the distance of the deep sphincter was（30.85±4.10）mm,the superficial sphincter was（26.04±3.48）mm,the varus degree of the subcutaneous part of EAS increased,and the anal-subcutaneous part angle was（56.87±16.18）°.During defecation stage,the EAS did the centrifugal movement and the anal canal opened,the distance of the bilateral deep sphincter was（37.51±5.17）mm,the superficial portion was（31.68±5.10）mm.The subcutaneous part of EAS tumbled outward,and the anal-subcutaneous part angle was（112.23±22.48）°.Conclusion The EAS maintains the anal continence by to squeeze,suspend,kinking,noose and seal the anal canal.The deep,superficial and subcutaneous part of EAS open in order,and the subcutaneous part does the flip-flop movement during defecation.