I. Embryological and anatomical basis of complete mesenteric resection
From an embryological point of view, the colonic and rectal mesentery are the remnants of the embryonic “dorsal mesentery”, between which the colon is wrapped and suspended from the posterior abdominal wall during intrauterine development, Treves found that the dorsal mesentery of the left and right colon was “fixed” to the posterior abdominal wall, and then the left and right colonic mesentery “disappeared” by “fusion” with the posterior peritoneum. In contrast, the transverse and sigmoid mesentery persists into adulthood, and he therefore concluded that the adult colonic mesentery is “discontinuous”. For this reason, the ascending and descending colon are also described in most current embryology and anatomy textbooks as “retroperitoneal” or “interperitoneal” organs, while the transverse and sigmoid colon are referred to as “intraperitoneal” organs.
In contrast, in surgical practice, even freeing the left or right side of the colon allows access to a natural anatomical plane between the colon and the retroperitoneum, and completes a complete mesenteric freeing of the colon in order to achieve complete resection of the corresponding blood supply, lymph nodes and adipose tissue structures contained therein. A similar view is held by Japanese scholars in the book “Illustrated Surgery: Interpreting the Essentials of Surgery from the Anatomy of the Membrane”.
In his surgical practice, Toldt found that the left and right colonic mesentery persisted in adulthood and that the left and right colonic mesentery were separated from the posterior abdominal wall by a continuous plane of tissue, which he called the lamina propria, or Toldt’s fascia, as it was later called. Later, Congdon and Zuckerandle et al. also confirmed that this view is closer to what is actually seen in surgery than the findings of Treves et al.
In 2014, Culligan et al. confirmed the existence of Toldt’s fascia between the mesothelial cell layer of the posterior lobe of the right and left colonic mesentery and the posterior peritoneum by electron microscopic studies of the colonic mesentery; and finally, by studying the surgical anatomy and histology, they proposed that the right and left colonic mesentery is continuous and intact, the small intestine mesentery is continuous with the colonic mesentery, and the sigmoid mesentery is continuous with the rectal mesentery. The colorectal mesentery is “completely extraperitoneal” through the attachment of Toldt’s fascia to the posterior peritoneum.
Nevertheless, Toldt’s view is rarely mentioned, whereas Treves’ view is still found in the anatomical and histoblastological literature. It is easy to see that the concept of “colonic mesentery” varies from embryological, anatomical or surgical perspectives.
The same is true for the concept of rectal mesentery. In anatomy, the lower and middle rectum is defined as an extraperitoneal organ, so there is no concept of rectal mesentery. In surgical practice, the rectal mesentery is a barrel-like structure wrapped by the visceral layer of the intrinsic fascia of the rectum, which includes the blood vessels, nerves, and lymphatic tissue of the rectum. This anatomical plane of the rectal mesentery is continuous with the Toldt plane.
II. Surgical necessity of tumor for complete mesenteric resection
TME with circumferential resectionmargin (CRM) has become a standardized surgical approach for rectal cancer, and studies have shown that TME can significantly reduce the local recurrence rate and significantly improve patient survival even without radiotherapy. According to foreign statistics in 2011, TME surgery reduced the local recurrence rate from 30% to 5%-8%, and increased the overall 5-year survival rate from 48%-50% to 68%-74% for all stages.
In 2009, Hohenberger et al [1] in Germany studied 1438 colon cancer cases and found that CME resected specimens were more oncologically compatible and reduced the 5-year recurrence rate of colon cancer from 6.5% to 3.6% and improved the 5-year survival rate from 82.1% to 89.1%. Therefore, it is believed that CME and TME are one and the same, and CME is an extension and development of TME.
West et al, on the other hand, evaluated 399 specimens of colon cancer surgery from the perspective of pathological examination and found that specimens obtained by surgery in the mesenteric plane of the colon had significantly greater resected mesenteric area and distance of the mesenteric margin from the lamina propria than specimens in which the surgical plane disrupted the mesenteric layer of the colon or entered the lamina propria (i.e., incomplete mesenteric defect of the colon); and the former had a significantly higher 5-year postoperative survival rate than the latter, especially in stage III patients. especially in stage III patients.
It is suggested that intraoperative access to the correct colonic mesenteric plane to obtain a more complete resection of the colonic mesentery may improve the survival of patients with colon cancer. In addition, the concept of CME itself emphasizes not only the integrity of the mesenteric level, but also the clearance of the central lymph nodes. Studies have found that central lymph node metastasis in colon cancer can range from 5% to 11%, and 0.8% of central lymph nodes can be jumped.
All of these studies confirm the need for CME from a pathological aspect. In addition, Faerden et al. confirmed the necessity of CME from the theory of lymphatic micrometastasis: micrometastases of less than 2 mm and free tumor cell clusters of less than 0.2 mm can exist in lymph nodes of the colonic mesentery, while one to five micrometastases may sometimes be present in a single tumor specimen. Theoretically, this explains the survival benefit of CME for patients with stage II colon cancer.
Although the study by West et al. suggests that CME results in more lymphatic clearance compared to conventional radical right hemicolectomy for right hemicolectomized colon cancer. However, whether it provides a greater survival benefit compared to conventional radical right hemicolectomy for right colon cancer has not been answered. Only some small case studies suggest that it can significantly reduce the local recurrence rate and improve the survival rate, especially the long-term survival benefit of lymph node positive patients. In 2012, West et al. combined German and Japanese studies comparing CME and D3 surgery, again suggesting that CME has more lymphatic clearance, but no further study was done on its long-term survival.
In addition, Hohenberger’s results have been questioned by scholars at home and abroad: the findings suggest that TME is an independent factor affecting the prognosis of rectal cancer, and the results of the studies available for CME compared with TME do not yet allow this conclusion; Hohenberger’s study did not indicate whether the surgery was performed by the same group of surgeons and did not conduct a multifactorial analysis; and his study Hohenberger’s study did not indicate whether the procedure was performed by the same group of surgeons and did not perform a multifactorial analysis; and his study spanned too long a period during which neoadjuvant therapy was emerging, ignoring the potential impact of the study. More evidence-based evidence is needed to support the long-term efficacy of CME.
The results of a recent Danish retrospective bulk case study showed that the 4-year disease-free survival rate was 85.8% (95% CI: 81.4-90.1) in the CME group and 75.9% (P=0.0010) in the conventional resection control group; multivariate Cox regression analysis showed that CME was a significant and independent predictor of higher disease-free survival for all patients, and this finding also applies to patients with UICC stage II and III; together, the above data can be concluded that CME in patients with stage I-III colon adenocarcinoma is closely associated with higher disease-free survival than conventional colectomy and may improve the prognosis of colon cancer patients [12]. It is believed that with the results of more high-quality studies, a more pertinent evaluation of CME will be available.
III. Accurate and complete mesenteric resection in laparoscopic colorectal surgery
In recent years, the use of high-definition and 3D camera systems has enabled better precise dissection and naked vascularization, and the accuracy of surgery has been improving; a series of key techniques for laparoscopic complete mesenteric resection have also been gradually established, such as intermediate approach, caudal approach, and “tenting” traction reveal, which makes laparoscopic antagonistic traction possible and the level of reveal and dissection more clear and precise.
These technical and equipment improvements have ensured complete laparoscopic resection of the mesentery. As for the efficacy of laparoscopic completion of CME, Storli et al [13] found in a controlled study of 251 laparoscopic versus open CME cases that the 3-year overall survival rate in the laparoscopic group was 84.5% and the tumor-free survival rate was 77.4%, comparable to open CME, while complications were lower than those of open surgery.West et al [14] studied specimens from laparoscopic versus open CME and found that laparoscopic and open CME specimens for colon cancer were identical.
The feasibility of laparoscopic CME and the efficacy of radical tumor treatment were initially confirmed. As for rectal cancer, the results of the COLOR II trial published in 2013 suggested that there was no statistically significant difference between the laparoscopic TME group and the open group in terms of positive peri-annular margin, distal margin, postoperative complications and postoperative mortality; while in the stratified study, the positive CRM rate of 9% in the laparoscopic group for low-grade rectal cancer was better than the 22% in the open group [15]. The long-term outcome results of COLOR II reported this year [16] showed that the local recurrence rate of TME for both laparoscopic and open rectal cancer was 5%, and the tumor-free and overall survival rates in the laparoscopic group were 74.8% and 86.7%, respectively, which were not statistically significant differences from the 70.8% and 83.6% in the open group.
IV. Similarities and differences in resection between CME and D3 radical surgery
In Europe and the United States, we have been cautious about D3 radical treatment of colorectal cancer because of the difficulty of surgery and postoperative complications, such as whether all staged cases can benefit more from D3 radical treatment, whether all surgeons have the ability to perform it, and whether it can be done laparoscopically, etc. Which is better or worse, and how to choose between CME and traditional D3 radical treatment of colon cancer? Is the proposed complete mesenteric resection a challenge to conventional D3 radical treatment?
In terms of indications for surgery, the 2012 Japanese Society for Colorectal Cancer (JSCCR) guidelines for colorectal cancer treatment suggest that D3 lymph node dissection should be performed for those who are suspected of having lymph node metastasis or whose tumor infiltration reaches the lamina propria and above as assessed during preoperative surgery. In China, it is also clearly stated in the 2010 Ministry of Health Colorectal Cancer Treatment Standard that D3 lymph node dissection is required for T2 to T4, N0 to N2 and M0 colon cancer. In contrast, CME is required to be performed in all cases.
The scope of D3 lymphatic clearance differs according to the right and left hemico-rectal systems. The scope of regional lymph node dissection performed in the colon belonging to the superior mesenteric artery system should include the following 3 stations.
(1) Para-intestinal lymph node dissection (station 1), depending on the actual tumor vascular blood supply, the corresponding length of intestinal canal at both ends should be removed;
(2) Intermediate lymph node dissection (station 2), dissection of lymph nodes distributed along the major and minor arteries related to the tumor blood supply;
(3) Central lymph node dissection (station 3), dissecting the lymph nodes at the beginning of the colonic artery from the superior mesenteric artery related to the blood supply of the tumor. In the inferior mesenteric artery system, the scope of paramedian lymph node dissection is the same as the former theory, but the lymph nodes distributed along the superior rectal artery, the middle rectal artery and the medial lymph nodes of the pelvic plexus are also classified as paramedian lymph nodes; the scope of intermediate lymph node dissection should include the lymph nodes around the trunk of the inferior mesenteric artery in the rectum in addition to the lymph nodes distributed along the major and minor arteries related to blood supply; and the central lymph node dissection specifically refers to The central lymph node dissection refers to the lymph nodes that travel along the inferior mesenteric artery between the beginning of the inferior mesenteric artery and the beginning of the left colonic artery.
In rectal tumors, upward lymphatic drainage is the main direction. Therefore, the clearance of lymphatic tissue at the root of the inferior mesenteric artery is the focus of lymphatic clearance for rectal cancer. For low and intermediate rectal cancer, the clearance of lateral lymph nodes is also one of the controversial points. Because lateral lymph node dissection often inevitably affects urogenital function to some extent, and on the other hand, with the development of integrated treatment such as radiotherapy and chemotherapy, and the implementation of the TME principle, only a small proportion of patients really benefit from lateral lymph node dissection, therefore, lateral lymph node dissection is currently not considered as a routine scope of radical rectal cancer dissection in China, Europe and the United States. In contrast, in Japan, lateral lymph node dissection is routinely performed when performing D3 radical surgery for low to intermediate progressive rectal cancer.
And CME in operation requires, in addition to complete colonic mesenteric resection, in fact also includes high ligation of the corresponding vessels and adequate lymphatic clearance required for D3 radical treatment as mentioned above. For example, in the case of right hemicolectomy, complete lymph node clearance of the ileum, right colon and the root of the middle colonic vessels is required; colon liver flexure tumors are found to have a positive lymph node rate of 5% and 4% in the head of the pancreas and the side of the greater curvature of the stomach, respectively.
Therefore, it is also necessary to dissect the right artery of the gastric omentum to clear the group 6 lymph nodes and to remove the gastric omentum along the vascular arch of the gastric omentum 10-15 cm away from the tumor; in some cancers of the hepatic flexure of the colon, lymphatic metastases can reach the level of the middle colonic artery, in which case, it is necessary to perform an extended right hemicolectomy and ligate the middle colonic artery at the root; while for tumors of the left hemicolectomy and splenic flexure, lymphatic metastases can reach The main lymphatic drainage of the transverse colon is located next to the middle colonic artery, but it may also be located next to the ileocolic artery or the left colonic artery, therefore, lymph nodes in the above mentioned areas should be considered for clearance during surgery of transverse colon tumors.
In practice, our scholars actually proposed the idea of “complete resection of the right Toldt’s fascia and the anterior duodenal fascia of the head of the pancreas” as early as 1996, but the concept of CME was not proposed at that time. Likewise, as early as 2001, some Chinese scholars completed laparoscopic radical colon cancer surgery using the concept of CME, but it was not summarized and published through high-quality clinical studies.
Thus, there is no substantial conflict between the CME concept and conventional D3 radical surgery in many aspects, and compared with conventional D3 radical surgery, CME simply places more emphasis on.
(1) dissecting along the root of the tumor draining vessels and maximizing lymph node clearance;
(2) Finding and maintaining the embryological anatomical surgical plane to ensure smooth and intact visceral fascia without defects;
(3) Based on the course of the colonic blood supply vessels, the extent of resection may be greater. We can consider that CME is not a new technique, but a new concept. Of course, as far as the surgery itself is concerned, the most important thing is to master the indications for the surgery, and whether to perform D3 radical surgery can be decided according to the TNM staging, while CME reflects the need for precise surgery.