Delancey J O, Toglia M R, Perucchini D
Department of Obstetrics and Gynecology, University of Michigan Medical Center, Ann Arbor, USA.
Obstet Gynecol. 1997 Dec;90(6):924-7. doi: 10.1016/s0029-7844(97)00472-9.
To examine the anatomy of the internal and external anal sphincters in the area of midline obstetric lacerations, to gain insight into sphincter damage and repair.
The length, craniocaudal extent, and overlap of the internal and external anal sphincters in the perineal body were measured in 17 cadavers. Further anatomic observations were made in four sets of whole pelvis cross-sections taken in the sagittal, coronal, and transverse planes. During the repair of 20 acute fourth-degree lacerations, observations were made to determine the internal sphincter visibility following birth.
The external and internal and sphincters overlap by 17.0 mm (standard deviation [SD] 6.9), with the internal sphincter lying between the external sphincter and the anal canal. The internal sphincter extends an additional 12.2 mm (SD 5.9) cranial to the proximal extent of the external sphincter, whereas the caudal margin of the internal sphincter lies 3.7 mm (SD 7.2) cranial to the distal margin of the external sphincter. In pregnant women who sustained a fourth-degree laceration, we found that the internal sphincter can be identified as a rubbery white layer adjacent to the anal submucosa lying between the external sphincter and the anal canal.
The internal anal sphincter lies between the anal mucosa and the external anal sphincter and extends more than a centimeter above the cranial margin of the external sphincter, a region where it is disrupted when a fourth-degree obstetric laceration has occurred.
研究会阴体中肛门内外括约肌在中线产科裂伤区域的解剖结构，以深入了解括约肌损伤及修复情况。
在17具尸体上测量会阴体中肛门内外括约肌的长度、头尾范围及重叠情况。在矢状面、冠状面和横断面的四组全骨盆横断面标本上进行进一步的解剖学观察。在修复20例急性IV度裂伤过程中，观察分娩后内括约肌的可视情况。
外括约肌与内括约肌重叠17.0mm（标准差[SD]6.9），内括约肌位于外括约肌与肛管之间。内括约肌在头侧比外括约肌近端范围额外延伸12.2mm（SD5.9），而内括约肌尾侧缘位于外括约肌远侧缘头侧3.7mm（SD7.2）处。在发生IV度裂伤的孕妇中，我们发现内括约肌可被识别为位于外括约肌与肛管之间、毗邻肛门黏膜下层的一层橡胶样白色组织。
肛门内括约肌位于肛门黏膜与肛门外括约肌之间，且在外括约肌头侧缘上方延伸超过1厘米，该区域在发生IV度产科裂伤时会受到破坏。
