肛提肌裂孔水平直肠前方结构的尸体解剖和组织学观察研究

Anatomical and histological investigation of the area anterior to the anorectum passing through the levator hiatus

目的了解肛提肌裂孔水平直肠前方肌群结构和神经血管组织的解剖关系。方法采用描述性研究的方法。选择福建医科大学解剖学教研室的3具男性半盆腔尸体标本,通过3种方式进行解剖,观察肛提肌裂孔水平直肠前壁的相关肌群结构和神经血管束(NVB),即(1)1个半盆标本,模拟直肠癌手术进行分离和观察;(2)1个半盆标本,从横断面,用莱卡刀片进行连续横断切(层厚约1 cm)观察;(3)1个半盆标本,选择正中矢状面进行观察和组织学研究。对典型层面进行苏木精-伊红染色,对肌群类型、神经和血管进行鉴别。结果(1)分离半盆尸体标本,于尿道膜部区域,约平肛提肌裂孔水平,见直肠纵肌向尾侧腹侧移行,其向腹侧移行肌束形成直肠尿道肌,向腹侧附着于尿道膜部。头侧毗邻前列腺尖,见会阴深横肌断面。在直肠尿道肌后缘与直肠纵肌之间见两侧NVB的交通血管。直肠尿道肌将直肠前壁向腹侧牵拉,参与形成肛直角。(2)由尾侧向头侧进行连续横断面观察,在肛门外括约肌层面,直肠纵肌向尾侧移行,于肛门外括约肌上缘分成2个肌束:一束向尾侧背侧移行,插入肛门外括约肌与肛门内括约肌构成的括约肌间隙中,形成联合纵肌;另一束向尾侧腹侧移行,填充于肛门外括约肌和球海绵体肌之间的空隙中;在会阴浅横肌层面,会阴浅横肌的薄层束状肌纤维横行穿插于直肠纵肌填充形成的会阴体区域;在直肠尿道肌和会阴深横肌层面,尿道膜部腹侧和两侧均有肥厚的尿道外括约肌环绕,背侧尿道外括约肌菲薄,由直肠纵肌向腹侧发出的直肠尿道肌附着。会阴深横肌的头侧腹侧见诸多NVB静脉团;在前列腺尖层面,NVB诸多血管分支直接支配直肠纵肌及其向腹侧移行形成的直肠尿道肌。直肠尿道肌向腹侧包绕尿道膜部和前列腺尖。直肠纵肌与前列腺的界限逐渐清晰,该处是经腹分离直肠前间隙的终点。(3)组织学观察,尿道膜部背侧尿道括约肌较薄弱,紧邻呈横纹肌结构的会阴深横肌,背侧毗邻NVB。直肠尿道肌填充于肛门内括约肌、会阴深横肌和两侧肛提肌构成的空间内。诸多迂曲的NVB静脉和细小神经纤维穿行于会阴深横肌和直肠尿道肌的肌纤维间。会阴浅横肌呈典型横纹肌纤维结构。根据大体解剖和组织学观察,三维模拟绘制肛提肌裂孔水平直肠前间隙的局部解剖结构。结论行经括约肌间切除或腹会阴联合切除术时,经腹入路沿邓氏筋膜后间隙分离至前列腺尖,直肠前方的外科平面消失。经会阴入路分离时,应以前列腺和双侧NVB为标记,靠近直肠侧切断直肠尿道肌。保留会阴浅横肌和会阴深横肌及其支配的NVB组织,并注意直肠尿道肌牵拉形成肛直角对分离路线的影响,避免尿道膜部损伤。

Objective To document the anatomical structure of the area anterior to the anorectum passing through the levator hiatus between the levator ani slings bilaterally.Methods Three male hemipelvises were examined at the Laboratory of Clinical Applied Anatomy,Fujian Medical University.(1)The anatomical assessment was performed in three ways;namely,by abdominal followed by perineal dissection,by examining serial cross-sections,and by examining median sagittal sections.(2)The series was stained with hematoxylin and eosin to enable identification of nerves,vessels,and smooth and striated muscles.Results(1)It was found that the rectourethralis muscle is closest to the deep transverse perineal muscle where the longitudinal muscle of the rectum extends into the posteroinferior area of the membranous urethra.The communicating branches of the neurovascular bundle(NVB)were identified at the posterior edge of the rectourethralis muscle on both sides.The rectum was found to be fixed to the membranous urethra through the rectourethral muscle,contributing to the anorectal angle of the anterior rectal wall.(2)Serial cross-sections from the anal to the oral side were examined.At the level of the external anal sphincter,the longitudinal muscle of the rectum was found to extend caudally and divide into two muscle bundles on the oral side of the external anal sphincter.One of these muscle bundles angled dorsally and caudally,forming the conjoined longitudinal muscle,which was found to insert into the intersphincteric space(between the internal and external anal sphincters).The other muscle bundle angled ventrally and caudally,filling the gap between the external anal sphincter and the bulbocavernosus muscle,forming the perineal body.At the level of the superficial transverse perineal muscle,this small muscle bundle headed laterally and intertwined with the longitudinal muscle in the region of the perineal body.At the level of the rectourethralis and deep transverse perineal muscle,the external urethral sphincter was found to occupy an almost completely circular space along the membranous part of the urethra.The dorsal part of the external urethral sphincter was found to be thin at the point of attachment of the rectourethralis muscle,the ventral part of the longitudinal muscle of the rectum.We identified a venous plexus from the NVB located close to the oral and ventral side of the deep transverse perineal muscle.Many vascular branches from the NVB were found to be penetrating the longitudinal muscle and the ventral part of rectourethralis muscle at the level of the apex of the prostate.The rectourethral muscle was wrapped ventrally around the membranous urethra and apex of the prostate.The boundary between the longitudinal muscle and prostate gradually became more distinct,being located at the anterior end of the transabdominal dissection plane.(3)Histological examination showed that the dorsal part of the external urethral sphincter(striated muscle)is thin adjacent to the striated muscle fibers from the deep transverse perineal muscle and the NVB dorsally and close by.The rectourethral muscle was found to fill the space created by the internal anal sphincter,deep transverse perineal muscle,and both levator ani muscles.Many tortuous vessels and tiny nerve fibers from the NVB were identified penetrating the muscle fibers of the deep transverse perineal and rectourethral muscles.The structure of the superficial transverse perineal muscle was typical of striated muscle.These findings were reconstructed three-dimensionally.Conclusions In intersphincteric resection or abdominoperineal resection for very low rectal cancer,the anterior dissection plane behind Denonvilliers'fascia disappears at the level of the apex of the prostate.The prostate and both NVBs should be used as landmarks during transanal dissection of the non-surgical plane.The rectourethralis muscle should be divided near the rectum side unless tumor involvement is suspected.The superficial and deep transverse perineal muscles,as well as their supplied vessels and nerve fibers from the NVB.In addition,the cutting direction should be adjusted according to the anorectal angle to minimize urethral injury.