Anatomical Identification Of Trans-Abdominal TME Terminal Line And Trans-Anal TME Start Line With Observation Of Peri-Rectal Fascial Complex And The Neurovascular Bundle

Background1-Despite Heald's emphasis on the anatomical importance and embryological background of the rectum,its mesentery and its relation with the surrounding pelvic fascial layers,he also questions the “perfect TME”.Perhaps this is due to the termination of the mesorectum is not well described.So,where is the end point of trans abdominal TME and the start point for trans-anal TME?2-Surgeons' anatomical orientation of DVF and its relation with the accompanying NVB has a direct impact on how to preserve the fascia.Till now there is no consensus on the regional anatomy of DVF and considered confusing for all pelvic surgeons.So,what is the regional anatomy of DVF and the exact location of NVB? How can we preserve the NVB?3-The lateral extension of Waldeyer's fascia and the lateral rectal attachment are challenging areas during rectal mobilization.The fascial arrangement and formation still not clearly illustrated and thus what is the lateral extension of Waldeyer's fascia and is there a relation between anterior,lateral and posterior rectal fasciae circumferentially ?MethodsIn this observational study,the distal mesorectum was examined in 4 ways: review of intra-operative [laparoscopic/robotic trans-abdominal(n=99)& trans-anal(n=25)]videos,MRI(n=99),cadaveric(n=28)and histopathologic specimens(n=44)of TME following extralevator abdominoperineal excision(ELAPE).The post surgical specimens were embedded into paraffin blocks.Hematoxylin and eosin(H&E)stain was used to confirm and examine the fascial composition of the terminal line.Masson's stain as a special stain for fascia demonstration was thereafter used to confirm the existence of the terminal line.The distance between the mesorectal end [anterior(12 o'clock),lateral(3or9 o'clock)and posterior(6 o'clock)] and both the dentate line and the anal verge was measured to identify the trans anal “start line” and assess the effect of the anorectal angle to reach this level through the rectal lumen.28 cadaveric specimens(male n=14 / female n=14)were included.The compositions of the peri-rectal fascial spaces(Denonvilliers' fascia,Waldeyer's fascia and the lateral rectal ligament)and the neurovascular bundle(NVB)were observed and recorded at different levels of dissection using a high-definition camera.Results1-“Terminal line” and “Start line” are different terms for the same thing which represent the distal mesorectal end level trans-abdominally and trans-anally respectively.It is a pearly white fascial structure extending posteriorly from 2 to 10 o'clock.Identified in 56.6%(56/99)of laparoscopic/robotic trans-abdominal and 56%(14/25)in trans-anal reviews.H&E histological stain showed that it was formed by the attachment of the presacral fascia to the proper fascia of the mesorectum at the level of the pelvic hiatus.Masson's stain confirmed its existence at the level and there was no extension of the mesorectal tissue below that level.2-28 cadavers and 44 ELAPE specimens were examined to identify taTME start line of dissection.The distance between the anterior mesorectal end(12o'clock)to the dentate line was significantly larger than the distance from the posterior mesorectal end(6o'clock)to the dentate line(25.14±5.24 mm,16.27±2.88 mm,P-value <0.001respectively).3-In front of the proper fascia of the mesorectum,the pre-rectal space in male consisted of three layers: the first layer(DVF)extended from the perineal body to the peritoneal reflection,the second layer enclosing the seminal vesicles and the third layer originated from the posterior bladder neck.Unlikely,only one layer(DVF)was found in female pre-rectal space.4-The proper fascia of the mesorectum and the Denonvilliers' fascia are almost inseparable at the level of the peritoneal reflection.The neurovascular bundle in male specimens was observed at the anterolateral aspect while its main part was found outside the DVF at the level of the semino-prostatic angle.5-DVF merges posterolaterally to meet the rectosacral fascia(Waldeyer's fascia)while merging anterolaterally.And thus,the lateral ligament is in fact a fascial amalgamation rather than a true ligament.Conclusions1-“Terminal line” and “Start line” both represent the mesorectal termination where the trans-abdominal dissection should end and the trans-anal proctotomy should start respectively.It looks like a semi-circumferential pearly white line extends between 2and 10 o'clock at the levator hiatus is an important landmark to identify the mesorectal termination.2-The distance between the terminal line(taTME start line)anteriorly and the dentate line is larger than the distance between the terminal line posteriorly and the dentate line.The anorectal angle imposes a significant effect to identify the mesorectal tail through the rectal lumen during taTME surgery.So,taTME start line shouldn't be a horizontal circumferentially equal line but it should be oblique line started anteriorly at distance deeper than posteriorly away from the dentate.That would guide us to where to start taTME proctectomy incision to avoid urethral injury anterior or missed mesorectal tissue posteriorly.3-Because the proper fascia of the mesorectum and DVF are almost fused together at the level of the peritoneal reflection,anterior rectal mobilization should be initiated 1cm anterior and above the peritoneal reflection then followed by dissection anterior to DVF first(pre DVF space)to ensure the mesorectal integrity in front of the rectum and then excised in U-shape manner 0.5 cm above the semino-prostatic angle.The dissection plane should be shifted to post DVF space by then.This partial preservation technique gives an enough space around the rectum in anatomically difficult and deep pelvis in obese patients to reach the distal end under complete vision.4-Collectively,understanding the concept of lateral extension of Waldeyer's fascia and its contribution of the lateral fascial amalgamation gives invaluable surgical guidance to dissect this difficult and critical area.After dissecting the posterior and anterior rectal spaces,the lateral rectal space should be upward anterior to downward posterior direction and find the Holy plan that guarantee intact mesorectal envelope and avoid injury of the pelvic plexus or NVB.