直肠手术的近期进展包括结肠全系膜切除和自主神经保留，因此结直肠手术医生必须了解直肠的胚胎发育，盆底的复杂解剖和淋巴结的分布。胚胎发育包括胚胎第一个月尾肠的形成，以及后来直肠和肛管的形成。直肠系膜包含血管和淋巴结。为了完全切除直肠系膜，手术医生应该遵循Heald描述的神圣平面，即位于直肠周围筋膜和盆腔筋膜之间的平面。这样，手术医生就很有机会保留盆腔自主神经，包括下腹上神经丛、右侧和左侧腹下神经，右侧和左侧下腹下神经丛。
Formation of the hindgut
During the first month of life, the embryo undergoes an anterior flexion, called cephalocaudal plication. The extoblaste stays on the convex pole of the embryo. The entoblaste engates the concave part and forms the anterior, median and posterior gut inside and the umbilical vesicle and allantoid outside the embryo.
The posterior gut, or hindgut, develops and becomes the splenic flexure, the descending colon, the sigmoid colon, the rectum and the anal canal. The distal part of this hindgut ends in a cul de sac called cloaca. At that point, the entoblaste is in contact with the ectoblaste, defining a membrane called the cloacal membrane.
后肠形成
在胚胎第一个月，胚胎发生前方曲折，称为头尾折叠。外胚层在胚胎的凸出一边。内胚层在胚胎的凹陷一边，内部形成前、中和后肠，脐泡和胚胎外的尿囊。
后肠，也叫尾肠，发育形成脾曲、降结肠、乙状结肠、直肠和肛管。远端部分终止于称为泄殖腔的凹陷。在此处，内胚层和外胚层接触，形成叫做泄殖腔膜的膜结构。
Formation of the rectum and anus
A transversal membrane progressively descends between the allantoid in the front and the hindgut behind, so that the cloaca is separated into two parts: the anterior one receives the name of urogenital sinus and the posterior the name of anorectal canal. Before the end of the second month of life, the septum joins the cloacal membrane and will form later, in the girl, the perineal fibrotic area. That membrane is divided into urogenital membrane in the front and anal membrane behind.
形成直肠和肛门
一个横膜逐步下降，位于前方的尿囊和后方的尾肠之间，这样泄殖腔形成两个部分，前方称为泌尿生殖窦，后方称为肛门直肠道。在胚胎发育第二个月之前，该膈连接到泄殖腔膜，然后，在女性形成会阴纤维区域。这个膜分为前方的泌尿生殖膜和后方的肛门膜。
Ultimate rectal development
The ectoblaste is then attracted by the anal membrane. This causes a depression called proctodaeum, that opens, so that the lower rectum has two components: the cranial part, which is from entoblastic origin and has a mesenteric artery blood supply, and the caudal part, which is from ectoblastic origin and has a internal iliac artery blood supply.
最终直肠发育
外胚层然后被肛膜吸引，形成一个凹陷，叫做原肛，开放后，下段直肠形成两个部分，头侧是内胚层来源，血供来自肠系膜动脉，尾侧部分是外胚层来源，血供来自髂内动脉。
Mesorectum
Anatomical definition
The term meso, coming from the Greek mesos, means intermediate or middle. In gross anatomy, the prefix meso pertains to two layers of peritoneum that suspend an organ. The rectum is closely applied to the sacral hollow so that the word mesorectum is inapplicable and strickely incorrect. Moreover, the term mesorectum does not appear in the Nomina Anatomica.
直肠系膜
解剖学定义
Meso，来源于希腊语mesos，是指中间。在大体解剖学中，meso这个前缀是指两层腹膜悬吊一个器官。直肠紧靠骶骨凹，因此直肠系膜并不适用，严格来说也不正确，而且，直肠系膜这一名词并未出现在解剖学名词中。
Clinical definition
A total mesorectal excision implies the complete excision of all fatty tissues enclosed within the perirectal fascia. The anatomic plane for rectal cancer excision the surgeon must follow is the one between the perirectal fascia and the pelvic fascia. The perirectal fascia takes its origin from the pelvic fascia. It covers the pelvic floor musculature and reflects as a strong sheath to encapsulate the rectum. It extends cranially around the ampulla posteriorly and laterally and blends with the visceral peritoneum overlying the rectum. It fuses anteriorly with the prostatoperitoneal aponeurosis.
The pelvic fascia covers the sacrum posteriorly and the lateral sides of the pelvis laterally. The neurovascular plane is under this sheet, protected from the surgeon's scissors. The pelvic and perirectal fascias are perforated at the point of the middle rectal arteries and rectal nerves penetration, which forms the rectal wings during dissection. Except at that level, the total mesorectal excision is blood free and the plane is easily entered, either by laparotomy or laparoscopically.
临床定义
直肠全息膜切除是指完全切除直肠周围筋膜包裹的脂肪组织。手术医生必须遵循的直肠癌切除解剖平面位于直肠周围筋膜和盆腔筋膜之间。直肠周围筋膜起源于盆腔筋膜。后者覆盖盆底肌层，并折返后包裹直肠形成强的筋膜。向尾侧直肠后方和侧方包裹壶腹部，并与覆盖直肠的脏层腹膜融合。在前方和前列腺会阴筋膜融合。
盆腔筋膜覆盖后方的骶骨和骨盆侧方。神经血管平面在其下方，从而保护不受到手术医生剪刀的影响。盆腔和直肠周围筋膜在直肠中动脉和直肠神经进入处有穿孔，后两者在解剖时形成直肠翼。除了在此水平，直肠全息膜切除在开腹或者腹腔镜手术中应该是无血，并且可以轻松进入。
Rectal blood supply
The rectum is vascularized by the superior, middle and inferior rectal arteries, which are all contained within the mesorectum. The left and right superior rectal arteries represent the terminal branches of the inferior mesenteric artery,after it has given the left superior colic artery and the superior, middle and inferior sigmoid arteries. The inferior mesenteric artery leaves the mesosigmoid and penetrates the mesorectum behind the upper part of the rectum, giving birth to the left and right superior rectal arteries, so that after having divided the first one at its origin, a slight traction either by laparotomy or laparoscopy opens the good plane of the mesorectum. The two superior rectal arteries distribute to the upper third of the rectum and contract may anastomoses with the two other following systems within the mesorectum and also within the submucosa.
The left and right middle rectal arteries are inconstant and, when present, are of small calbre. They come from the ipsilateral internal iliac artery and pass through the pelvic fascia and the perirectal fascia toward the rectum wall. They distribute to the middle third of the rectum.
直肠血供
直肠血供来源于直肠上、中和下动脉，所有均在直肠系膜内。左右直肠上动脉均是肠系膜下动脉的终末分支，在其发出左结肠上动脉和乙状结肠上、中和下动脉后。肠系膜下动脉离开乙状结肠系膜，在直肠上段后方穿过直肠系膜，发出左右直肠上动脉。因此在起源处离断一个动脉后，开腹或者腹腔镜下轻微牵拉就可以打开直肠系膜平面。直肠上动脉供应直肠上三分之一，并在直肠系膜和粘膜下和其它两条动脉有广泛吻合。
左右直肠中动脉不恒定，如果出现，直径很小。起源于同侧髂内动脉，穿过盆腔筋膜和直肠周围筋膜，到达直肠壁，供应直肠中段。
The left and right inferior rectal arteries come from the internal iliac arteries too, via the pudendal arteries that lie in the Alcock canal, just against the internal side of the ischiatic tuberosity. These arteries distribute to the inferior third of the rectum and the anal canal. The rectal veins are close to the corresponding arteries. The inferior and middle rectal veins end in the caval system iva the iliac veins and the superior rectal veins join the portal system via the inferior mesenteric vein, so that a physiological portocaval anastomosis is described around the rectum.
左右直肠下动脉同样起源于髂内动脉，通过Alcock管内的阴部内动脉，正好位于坐骨结节的内侧，供应直肠下三分之一和肛管。直肠静脉靠近相应的动脉。直肠下和中静脉通过髂内静脉回流到腔静脉，直肠上静脉通过肠系膜下静脉回流到门静脉，因此在直肠周围形成生理性的门-下腔静脉吻合。
Rectal lymphatics
Lymphatic nodes gather in three groups: those against and around the rectal muscular wall called the distal or perirectal group which are all comprised within the mesorectum, those along the mesenteric artery called the intermediate group and the last one at the origin of the inferior mesenteric artery called the proximal group. All carcinoma tumor cells will drain through these three groups,except the very low rectal and anal cancers that can drain through inguinal nodes. Exceptionally, very massive tumors are associated with iliac nodes invasion, like for instance prostate cancer does.
直肠淋巴
淋巴结聚集成三组，围绕直肠肌层的称为远端或者直肠周围组，均位于直肠系膜内，沿着系膜动脉的称为中间组，最后一组位于肠系膜下动脉起源处，称为近端组。所有肿瘤细胞都通过这三组引流，除了非常低的直肠和肛管癌可以通过腹股沟淋巴结引流。偶尔情况下，非常大的肿瘤发生髂内淋巴结侵犯，类似于前列腺癌。
Autonomic pelvic nerves
The pelvic nerves comprise the sacral plexus devoted to the pelvic musculature and the inferior limbs(L4,L5,S1,S2 and S3), the pudendal plexus for the pelvic viscera and the external genital organs(S2,S3 and S4) and the autonomic pelvic plexuses that are intricated with the prededing ones(superior and inferior hypogastric plexuses). When the rectum and the mesorectum are freed following the good plane, there is no risk of damaging these nerves. At the end of thsi stage, the superior hypogastric plexus formed b the thoracolumbar sympathetic plexuses(devoted to ejaculation in men) appears in a triangular shape that fives the left and right inferior hypogastric plexuses that are of quadrangular shape lower in the pelvis and receive posteriorly other branches from the second, third, fourth and fifth anterior sacral roots. These nerves are from parasympathetic origin and comprise the nervi erigente(devoted to erection in men). The inferior hypogastric plexuses five branches to the internal genital organs, urinary bladder, rectum and anal canal. In case of a huge tumor invading the perirectal fascia or even the pelvic fascia or more, the surgeon may face teh problem of sectioning one or the two hypogastric nerves or, lower, the hypogastric plexuses. As a consequence, the patient will experience often permanent and irreversible urinary and sexual disturbances. In smaller tumors, i.e. T3 or less, there should be no such functional disorders, after having mentioned that psychological trauma f a heavy operation, radiotherapy or pain medications can in themselves induce sexual troubles.
盆腔自主神经
盆腔神经包括骶丛，支配盆腔肌肉和下肢（L4,L5,S1,S2和S3)；阴部内丛，支配盆腔脏器和外生殖器（S2,S3和S4）；自主神经丛，与腹下神经上、下丛交织分布。遵循良好平面分离直肠及其系膜时，不会损伤这些神经。在这一阶段结束时，有胸腰交感神经丛发形成的下腹神经上丛呈三角状，发出左右腹下神经。后者再汇入左右下腹下神经丛，呈方形位于盆底部，在后方接受了骶2-5神经前干的分支。后者为副交感神经起源，含有勃起神经。下腹下神经丛发出分支到内生殖器，膀胱，直肠和肛管。对于侵犯直肠周围筋膜的巨大肿瘤，甚至侵犯盆腔筋膜者，手术医生面临需要离断一条或者二条腹下神经，或者更低的腹下神经丛。导致患者出现永久不可逆的泌尿和性功能障碍。在小一些的肿瘤，例如I3或者更低，则应该不会这些这些问题。但大手术的心理创伤，放疗或者疼痛用药本身就可以导致性功能障碍。
来源：Faucheron JL. Pelvic anatomy for colorectal surgeons. Acta Chir Belg. 2005 Sep-Oct;105(5):471-4. doi: 10.1080/00015458.2005.11679762. PMID: 16315828.
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