Hsu Yvonne, Fenner Dee E, Weadock William J, DeLancey John O L
Pelvic Floor Research Group, Division of Gynecology, Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan 48109-0276, USA.
Obstet Gynecol. 2005 Dec;106(6):1259-65. doi: 10.1097/01.AOG.0000189084.82449.fc.
To use magnetic resonance images of living women and 3-dimensional modeling software to identify the component parts and characteristic features of the external anal sphincter (EAS) that have visible separation or varying origins and insertions.
Detailed structural analysis of anal sphincter anatomy was performed on 3 pelvic magnetic resonance imaging (MRI) data sets selected for image clarity from ongoing studies involving nulliparous women. The relationships of anal sphincter structures seen in axial, sagittal, and coronal planes were examined using the 3-D Slicer 2.1b1 software program. The following were requirements for sphincter elements to be considered separate: 1) a clear and consistently visible separation or 2) a different origin or insertion. The characteristic features identified in this way were then evaluated in images from an additional 50 nulliparas for the frequency of feature visibility.
There were 3 components of the EAS that met criteria as being "separate" structures. The main body (EAS-M) is separated from the subcutaneous external anal sphincter (SQ-EAS) by a clear division that could be observed in all (100%) of the MRI scans reviewed. The wing-shaped end (EAS-W) has fibers that do not cross the midline ventrally, but have lateral origins near the ischiopubic ramus. This EAS-W component was visible in 76% of the nulliparas reviewed.
Three distinct external anal sphincter components can be identified by MRI in the majority of nulliparous women.
利用成年女性的磁共振图像和三维建模软件，识别具有明显分离或不同起止点的肛门外括约肌（EAS）的组成部分和特征。
从正在进行的涉及未生育女性的研究中，选择3套盆腔磁共振成像（MRI）数据集，对肛门括约肌解剖结构进行详细的结构分析。使用3-D Slicer 2.1b1软件程序检查在轴位、矢状位和冠状位平面上观察到的肛门括约肌结构的关系。括约肌各部分被视为分离的条件如下：1）有清晰且始终可见的分离；或2）有不同的起止点。然后在另外50例未生育女性的图像中评估以这种方式识别出的特征的可见频率。
有3个EAS组成部分符合“分离”结构的标准。主体部分（EAS-M）与皮下肛门外括约肌（SQ-EAS）通过一个在所有（100%）复查的MRI扫描中均可观察到的清晰分隔而分开。翼状末端（EAS-W）的纤维在腹侧不穿过中线，但其外侧起点靠近耻骨坐骨支。在76%的被复查未生育女性中可看到这个EAS-W组成部分。
在大多数未生育女性中，通过MRI可识别出3个不同的肛门外括约肌组成部分。
