Anatomic Study Of The Anterior Structure Of The Terminal Rectum And Its Adjacent Relationship In Adult Males

ObjectiveThe terminal rectum is anterior to the lower margin of the prostate and posterior to the terminal rectum at the caudal tip of the coccyx.The structure of the front end of the rectum is delicate,complicated,closely related and bears important physiological functions,which is the key point and difficulty of the operation of the rectum and anus.In this study,cadaver dissection was used to observe the characteristics of the anterior adjoint structure of the terminal rectum in adult males and the correlation between the adjoint structure and the adjacent structure.By measuring the Rectourethralis Muscle(RUM)and Perineal Body(PB),as well as the spatial distance between RUM and PB and the adjoint structure,the anatomical basis was provided for the operation of the rectum and anus.The results were compared with Magnatic Resonance Imaging(MRI)images to provide evidence for Imaging recognition and surgical planning.Methods1.In this study,20 adult male cadavers from the department of basic medicine of xi'an medical college and the department of basic medicine of xi 'an jiaotong university were dissected into pelvic specimens.The cadavers showed no signs of pelvic surgery or disease,and all cadavers were fixed with 10% formalin solution artery perfusion.All pelvic specimens were incised in midsagittal position via the connection between the pubic symphysis and the sacral median,to observe the tissue structure morphology,walking and the spatial relationship between the anterior tissues of the terminal rectum,and to measure the anatomical data of RUM and PB and the relative distance between them and the adjacent important anatomical markers with vernier caliper for analysis.2.Drawn between January 2019 and December 2019 in shaanxi province people's hospital line of the male patients of pelvic MRI imaging data of 30 cases,under the guidance of nuclear magnetic resonance room in the diagnosis of the physician to read,according to the anatomical observations identify terminal rectum anterior anatomical structures and their mutual relations with neighbours,and measure the RUM,PB and RUM and PB and adjacent to the space distance of the structure.Results1.The anatomical morphology of RUM and its spatial relationship with adjacentstructures.RUM starts from the longitudinal muscle of the rectum and comes out from the longitudinal muscle of the anterior wall of the rectum behind the prostate.It forms a branch at the level of the tip of the prostate.The anterior bundle travels to the ventral caudal side and reaches the dorsal part of the urethra membrane.After parting from RUM,the longitudinal rectum muscle runs to the caudal side,between the Internal Anal Sphincter(IAS)and the External Anal Sphincter(EAS),and some of its fascicles branch into the EAS.After measurement:(1)Bilateral average width of RUM(left-right diameter length of RUM): 9.40±4.07mm(range 6.48-13.04mm);(2)The average distance from the beginning of RUM to the branch point of RUM: 13.67±8.82mm(range 10.10-20.08mm);(3)The mean distance between the branch of RUM and the end of the anterior beam: 10.86±2.21mm(range 8.08-14.10mm);(4)The mean distance between the branch point of RUM and the end point of posterior beam: 9.99±3.86mm(range 6.96-14.02mm);(5)The mean vertical distance from the start of RUM to the dentate line: 29.15±9.04mm(range24.78-32.06mm);(6)Mean vertical distance between branch point of RUM and toothed line:17.29±5.11mm(range 13.44-20.96mm);(7)Mean vertical distance from the dead point of the anterior beam of RUM to the dentate line: 15.20±10.65mm(range8.50-21.12mm);(8)Mean vertical distance from the dead point of posterior RUM to the dentate line:10.08±5.48mm(range 6.16-15.48mm);(9)Mean vertical distance from the end of the longitudinal muscle of the rectum to the dentate line: 8.35±4.49mm(range5.20-13.26mm).This was measured on pelvic MRI:(1)Average width of RUM(left-right diameter length of RUM): 9.05±4.85mm(range 5.88-13.02mm);(2)The average distance from the beginning of RUM to the branch point of RUM:12.60±4.76mm(range9.22-16.52mm);(3)The mean distance between the branch point of RUM and the end point of posterior beam:10.79±5.69mm(range 6.04-14.62mm);(4)The mean distance from the origin of RUM to the anal border:29.57±5.68mm(range 26.72-33.4mm);(5)Mean distance from branch of RUM to anal border:19.47±5.59mm(range: 15.64-23.26mm);(6)Mean distance from the end of posterior fasciculus RUM to the anal border:14.85±7.07mm(range 10.18-18.76mm).2.The anatomical morphology of PB and its adjacent relationshipPB is an irregular strip located between the rectum,urethra and prostate.Its parenchyma is a tendinous structure formed by the perineal muscle in the central perineum,and its boundary is the fusion of the various muscle bundles at PB.RUM joins in the cephalic side to form its upper boundary.From the ischial tuberosity Perineal shallowhorizontal Muscle(Superficial Transverse Perineal Muscle,STPM)and from the sciatic the Perineal Deep Transverse Muscle(Deep Transverse Perineal Muscle,DTPM)in lateral integration into the PB,the two muscles a Deep shallow,common PB at the fusion of the lateral boundary.The external sphincter of urethra and bulbar cavernosum muscle were located in front of the caudal side,and the EAS confluence was located in the rear,forming the lower bound of PB.The length of PB diameter was measured by cadaver:(1)Average length of PB left and right diameters: 15.74±9.66mm(range 11.58-22.08mm);(2)Average length of PB head and tail diameter: 12.68±8.43mm(range 9.12-18.72mm);(3)Average length of PB front and rear diameters: 9.66±0.77mm(range 8.28-11.66mm).This was measured on pelvic MRI:(1)Average length of PB left and right diameters: 14.47±6.37mm(range: 10.02-18.32mm);(2)Average length of PB head and tail diameter: 10.58±4.79mm(range: 7.12-14.22mm);(3)Average length of PB front and rear diameters: 10.37±4.56mm(range: 7.04-14.1mm).3.Pelvic MRI demonstrates the anatomic structure of the anterior end of the rectumRUM and PB anatomical data and the spatial distance between RUM and PB and adjacent structures were measured in pelvic MRI images.After measurement:According to the anatomical features of the structure of the anterior end of the rectum and combined with the anatomical features of the three-dimensional positioning image of the pelvic MRI,the structures of STPM,DTPM,urethral cavernosum muscle,ischial cavernosum muscle,PB,rectolongitudinal muscle,RUM,IAS,EAS and so on can be clearly identified.It can provide good image support for imaging diagnosis and surgical scheme design.Conclusion1.RUM is a squamous structure from the longitudinal muscle of the anterior wall of the rectum to RS and PB.For both transabdominal and transanal TME,the transverse rupture of RUM is required between the origin of RUM and the branch point,with an average distance of13.67 mm.Therefore,it is not appropriate to dissociate along the direction of muscle fibers.If the dissociation exceeds the branch point,careful dissection should be conducted.After the excision of levator ANI by APR surgery,the finger can be inserted into the cranial side of RUM to assist in locating the tip of the prostate gland,and the RUM can be severed behind the tip of the prostate gland to avoid damaging the urethra.2.PB is the central junction of the pelvic floor muscles at the distal end of the rectum.During perineal operation of rectal and anal surgery,the EAS should be dissociated from STPM and DTPM,and the transverse muscles in front of the EAS should be avoidedto avoid PB injury.From broken anal levator and pelvic diaphragm,on both sides by anal levator is off to the rectum in front of the two forces,PB end diameter is 12.68 mm,head to the side should be paid attention to free more than the distance for the upper bound of the PB,as a bundle of RUM after check point here,along the RUM bunch of head to the side walk XingYao after about 10 mm,can find the RUM branch points,between RUM branch point and the starting point from the RUM and the clearance between the prostate and can be safely to the rectum,should avoid direct anatomical PB back,can damage because of unclear boundaries of PB,even damage the membrane urethra.Mastering the anatomical relationship between RUM,PB and their adjacent tissues can improve the efficiency of rectal cancer surgery,reduce the difficulty of surgery,and reduce the occurrence of surgical accidents.3.MRI images can identify the relationship between the anterior structure of the terminal rectum and its adjacency.There are many adjacent structures in front of the rectum in males with complicated relationships.Preoperative MRI can clearly show the structures here,so as to guide the surgical approach and resection range.During the operation,the anatomical structure and the relationship between them should be correctly identified according to the imaging data,so as to guide the standardized and precise operation of perineal surgery.