Anatomical Study Of The Posterior Structures Of The Rectum And Its Adjacent Relationship In Adults

Objective:The anatomical structure of the posterior rectum and its adjacent relationship in adults were observed by stratified anatomical method,so as to provide applied anatomical basis for the choice of approach,motivation layers and the protection of pelvic nerve in rectal surgery.Methods:Ten adult pelvic specimens(5 males and 5 females)fixed with 10% formalin solution were dissected by the method of stratified anatomy.Anatomical method:(1)The pelvis was dissected at the left sacroiliac joint in sagittal position,and the pelvic segment of urogenital stratum,presacral fascia,rectosacral fascia,rectosacral ligament were observed.(2)The semi-pelvic specimens were obtained from the median sagittal position of the pelvis.The pelvic segment of urogenital stratum,rectosacral fascia,rectosacral ligament and Hiatal ligament were further dissected and observed,and the position,morphological characteristics and mutual adjacent relationship of each anatomical structure were observed.(3)In the process of dissection,the important anatomical structures were measured with a vernier caliper,stained and photographed.Results:1.Behind the rectum,the urogenital stratum is covered by the vesciral urogenital fascia and the parietal urogenital fascia,which contains bilateral hypogastric nerves and adipose tissue;the urogenital stratum extends to the caudal and merges with the dorsal rectum proper fascia at the level of sacral 4 vertebrae.2.The presacral fascia is located on the dorsal side of the urogenital stratum,covering the presacral venous plexus,extending to the psoas fascia in the cranial side,extending to the levator ani fascia in the caudal side.The presacral fascia extends to both sides as the fascia covering the surface of piriformis muscle,internal obturator muscle,pelvic splanchnic nerve,internal iliac vessels and obturator vascular nerve bundle.3.At the level of sacral 4,the retrorectal space is formed between the dorsal rectum proper fascia and the vesciral urogenital fascia,which continues with the prerenal space between the sigmoid mesocolonic fascia and the prerenal fascia.The presacral space is formed between the parietal urogenital fascia and the presacral fascia,which extends to the retrorenal space between the retrorenal fascia and the psoas fascia in the cranial side,and continued with the superior levator ani space between the dorsal rectum proper fascia and the levator ani fascia in the caudal side.4.Rectosacral fascia is located at the level of sacral 2 to sacral 4,which shape is the adhesion between the presacral fascia and the rectal proper fascia.It can be found in many places,in which there are no blood vessels passing through,and plays the role of hanging and fixing the lower segment of the rectum.The occurrence rate is 100%,the width is about1.17 ±0.22 cm(range 0.66-1.60cm),and the length is about 0.61 ±0.11 cm(range0.42-0.75cm).5.The Rectosacral ligament is located in the midline area from sacral 5 to the front of the coccyx.It is a tubular ligament-like structure formed by the presacral fascia at the junction of the sacrum and coccyx.It contains the terminal branch of the median sacral vessel entering the dorsal mesentery of the end of the rectum.The occurrence rate is 40%,and the width is about 0.46±0.09cm(range 0.33-0.55cm),and the length is about 0.77 ±0.22cm(range 0.56-1.11cm).6.Hiatal ligament is the fusion of the end of the rectum and the pelvic floor muscle,including the fascia site located on the cranial side,that is,the fusion of the proper fascia at the end of the rectum and the levator ani fascia.It also includes the muscle site located on the caudal side,formed by the longitudinalrectum smooth muscle fibers extending into the skeletal muscle fibers of the pelvic floor muscle.The smooth muscle extends in the anterior and posterior part of the end of the rectum,and the posterior part is more obvious in the posterior midline of the rectum,forming a tough white anal-caudal ligament.Conclusion:1.In the posterior of the rectum,there is a urogenital stratum between the dorsal rectum proper fascia and the presacral fascia,and the above three anatomical layers form the retrorectal space and the presacral space-superior levator ani space.During the operation,the urogenital stratum must be cut off before entering the presacral space-superior levator ani space,and the bilateral hypogatric nerve should be protected when the urogenital stratum is cut off.2.The rectosacral fascia is found at the level of sacral 2-sacral 4 and occurs constantly,which is formed by the adhesion between the presacral fascia and the dorsal rectum proper fascia,which is most consistent with the description of Waldeyer’s fascia in the classical literature.During the operation,we should pay attention to expose the state of the rectosacral fascia and avoid dissociating into the posterior part of the presacral fascia,so as to avoid the injury and bleeding of the presacral venous plexus.3.The rectosacral ligament is commonly found in the midline anterior sacral 5 to coccyx region,with an occurrence rate of about 40%.The presacral fascia wraps the terminal branch of the median sacral vessel into the dorsal mesentery of the rectum.Its structure is different from the rectosacral fascia.They should be two anatomical concepts.Pay attention to hemostasis during amputation.The role of this structure in lower rectal tumor metastasis needs to be studied.4.The Hiatal ligament includes the fascia site on the cranial and the muscle site on the caudal.The muscle site is weak on both sides of the end of the rectum,and is more obvious in the anterior part of the rectum and the posterior part of the rectum.During the operation,it is easy to enter the internal and external sphincter space after cutting the fascia site of Hiatal ligament on both sides of the rectum,which can be used as a guide to determine and cut off the anococcygeal ligament,which can dissociate the terminal rectum in the surgical anal canal.