Table of Contents  

Weber: Surgery for colon cancer – complete mesocolic excision

Introduction

In 1982, the concept of total mesorectal excision (TME) for rectal cancer was introduced by Heald et al.1 This technique of operation improved the outcome of rectal cancer significantly: survival rates could be increased and local recurrence rates could be diminished. The technique of TME is focused on sharp dissection of the anatomical planes (‘holy plane’2), thus obtaining an optimized specimen with intact layers. This concept of preparation was accepted worldwide for rectal surgery and soon became the ‘gold standard’ for treatment of this malignant disease.

However, the anatomical planes are not limited to the mesorectal planes. Because of the embryological development, those layers can be found in the whole gastrointestinal tract. Therefore, the technique of sharp dissection of the anatomical planes can be transferred to colon cancer surgery, too.3

In 2009, Hohenberger et al.4 introduced the concept of complete mesocolic excision (CME) for colon cancer. This concept has two components. As in rectal cancer surgery, the anatomical layers are separated by sharp dissection; the visceral plane is separated from the parietal plane. A CME specimen features an intact package of the tumour and its main lymphatic drainage with no tears in the fascial layers on both sides of the mesocolon. In addition, a central dissection of the relevant tumour-feeding arteries right at their origins (‘high tie’) is performed, in tumours on the right-hand side of the body at the level of the superior mesenteric artery (SMA), in tumours on the left-hand side of the body at the level of the inferior mesenteric artery (IMA), or the aorta. This enables one to remove as many lymph nodes as possible.

Below the parietal plane, the anatomical structures such as the ureter and the sympathetic nerves are left untouched and can be fully preserved. Only locally advanced tumours are excluded from this.

Like TME quality for rectal cancer, the specimen quality for colon cancer, depending on the plane of surgery, can be classified into ‘good’ (mesocolic plane), ‘moderate’ (intramesocolic plane) and ‘poor’ (muscularis propria plane). Oncological benefits of mesocolic plane surgery could be demonstrated.5 Consequently, using an operating strategy based on the principles of CME, in over 90% of cases a ‘good’ specimen quality can be achieved.6

General considerations of surgery for colon cancer

As colon carcinoma is one of the most common malignant tumours worldwide,7 and as most of these tumours are removable by surgery alone, every surgeon performing colon cancer operations should understand the basic principles of colon cancer surgery, which is based on the lymphatic drainage of these tumours. Except for far advanced cases, lymphatic metastasis follows predictable courses.

The metastatic spread of colorectal tumours occurs within the lymphatic vessels along the relevant supplying arteries. Potential node metastases are firstly located in the epicolic and paracolic lymph nodes, but not more than 10 cm away from both sides of the primary tumour.8,9 The metastatic spread then follows the supplying arteries towards the centre, to the intermediate nodes, and finally to the main (or principal) nodes at the origin of the feeding arteries (Figure 1).

FIGURE 1

Arterial supply and lymph node stations in colorectal cancer by the example of sigmoid carcinoma (modified from Weber K, Göhl J, Lux P, Merkel S, Hohenberger W. Principles and technique of lymph node dissection in colorectal carcinoma [in German]. Chirurg 2012; 83:487–9810). 1, ileocolic artery; 2, right colic artery (*if present); 3, middle colic artery; 4, left colic artery; 5, sigmoid arteries; 6, superior rectal artery.

HMJ-9-3-10-fig1.jpg

An operation on colon carcinoma is always surgery on the lymphatic drainage of this tumour. Preoperatively, it cannot be determined for certain if a cancer has already colonized lymph nodes in its drainage area. Intraoperatively, it cannot be stated whether or not nodes are affected, because size, consistency and appearance do not correlate with true colonization. It has been reported that more than 50% of the nodes involved are smaller than 5 mm in diameter and thus clinically inconspicuous.11,12 In contrast, only 25% of cases involve enlarged nodes in the drainage area larger than 1 cm in diameter.12

Taking all this into consideration, it is always necessary for all curative colon cancer operations to remove the tumour-bearing bowel including the mesocolic area with possibly involved lymph nodes. The extent of colon resection is dependent on the necessary mesocolic resection, which depends in turn on the separation of the tumour-feeding arteries.

Extent of resection for different tumour locations

Carcinomas of the caecum and the ascending colon metastasize towards the centre within the lymphatic vessels along the ileocolic and right colic arteries.

To remove the whole lymphatic drainage of these tumours, it is necessary to separate these two arteries at their origin at the SMA (Figure 2). Depending on the vascular separation, the bowel has to be separated at the terminal ileum and the right colonic flexure (so-called right hemicolectomy) (Figure 3).

FIGURE 2

Lymphatic drainage along supplying arteries in the mesocolon dependent on the location of the primary tumour (*if present) (modified from Weber K, Göhl J, Lux P, Merkel S, Hohenberger W. Principles and technique of lymph node dissection in colorectal carcinoma [in German]. Chirurg 2012; 83:487–9810).

HMJ-9-3-10-fig2.jpg
FIGURE 3

Right hemicolectomy, amount of mesocolic and bowel resection (from Weber K, Perrakis A, Hohenberger W. Standard therapy in colon carcinoma [in German]. Chir Praxis 2010; 72:25–3516).

HMJ-9-3-10-fig3.jpg

Except for very far advanced carcinomas, no lymphatic metastases are observed in the mesentery of the terminal ileum;13 therefore, it is normally sufficient to separate the ileum 10 cm above Bauhin’s valve.

Vascular anatomy close to the right colonic flexure is very variable. A true right colic artery originating from the SMA is observed in only about 15% of people.14,15 In most other cases, the right colon is supplied by a right branch of the middle colic artery in addition to the ileocolic artery. In absence of a true right colic artery, the branch described should be ligated at its origin (Figure 4).

FIGURE 4

Situs after right hemicolectomy with CME in the absence of a true right colic artery (from Hohenberger W, Weber K, Matzel K, Papadopoulos T, Merkel S. Standardized surgery for colonic cancer: complete mesocolic excision and central ligation. Technical notes and outcome. Colorectal Dis 2009; 11:354–644).

HMJ-9-3-10-fig4.jpg

An obligatory resection of the greater omentum is not necessary in these carcinomas. Only if parts of the omentum are directly fixed to the tumour do they have to be removed.

In the case of an advanced tumour with adherence to other organs (e.g. small bowel, abdominal wall), the carcinoma must not be separated from these structures to avoid cancer spread in the peritoneal cavity, as real tumour invasion can be found in 50%.17 A multivisceral resection en bloc is always mandatory in these cases.

Carcinomas of the right colonic (hepatic) flexure and the right third of the transverse colon can metastasize along the ileocolic, the right colic (if present) and the middle colic arteries (Figure 2).

After dissection of these vessels centrally, the bowel has to be separated in the left third of the transverse colon and in the terminal ileum (so-called extended right hemicolectomy). The arterial perfusion of the remaining splenic flexure and the left colon then comes from the IMA (Figure 5).

FIGURE 5

Extended right hemicolectomy (from Weber K, Perrakis A, Hohenberger W. Standard therapy in colon carcinoma [in German]. Chir Praxis 2010; 72:25–3516).

HMJ-9-3-10-fig5.jpg

Apart from regular mesocolic metastasis, aberrant lymphatic spread is observed in these tumours to omental lymph nodes18 and to infrapyloric lymph nodes8 or nodes at the greater curvature of the stomach located at the gastroepiploic arcade (Figure 6). In carcinomas with positive mesocolic lymph nodes, these extramesocolic nodes are involved in up to 16% of cases.19,20 In advanced tumours, node metastases can even be found at the origin of the right gastroepiploic artery above the pancreatic head.19 Therefore, the right part of the greater omentum is removed together with the tumour and must not be separated from it. The omentum can be divided at a minimum distance of 10 cm aboral of the cancer; the left part of the omentum can thus be preserved. Like the omental separation, the gastroepiploic vessels at the greater curvature of the stomach are also divided at a minimum distance of 10 cm left of the tumour. On the right side of this separation, the lymph nodes are removed together with the vessels at the greater curvature of the stomach. After removal of the infrapyloric nodes, the dissection is completed by separating the right gastroepiploic vessels at their origin by dissecting the lymph nodes above the pancreatic head (Figure 7).

FIGURE 6

Location of potential aberrant lymph node metastasis dependent on the location of the primary tumour (modified from Weber K, Göhl J, Lux P, Merkel S, Hohenberger W. Principles and technique of lymph node dissection in colorectal carcinoma [in German. Chirurg 2012; 83:487–98]10).

HMJ-9-3-10-fig6.jpg
FIGURE 7

Site of operation following extended right hemicolectomy for carcinoma of the right third of the transverse colon. Dissection of the mesenteric root and pancreatic head. Central ligation of the right and middle colic arteries.

HMJ-9-3-10-fig7.jpg

Carcinomas of the middle third of the transverse colon usually metastasize along the branches of the middle colic artery. Another pathway is along the left colic artery towards the IMA (Figure 2). Therefore, to remove those tumours it is necessary to ligate the middle colic artery centrally and to dissect the left colic artery right on its origin at the IMA. The colon is divided below the hepatic flexure on the right side and within the proximal sigmoid on the left side (Figure 8).

FIGURE 8

Resection of transverse colon carcinoma (from Weber K, Perrakis A, Hohenberger W. Standard therapy in colon carcinoma [in German]. Chir Praxis 2010; 72:25–3516).

HMJ-9-3-10-fig8.jpg

As in tumours of the hepatic flexure, aberrant lymph node metastases can be found in the greater omentum and along the gastroepiploic arcade at the greater curvature of the stomach.18,19 Therefore, an omental resection should be performed at a minimal distance of 10 cm on both sides of the tumour, leaving the fixed omentum untouched on the carcinoma. The gastroepiploic arcade at the greater curvature of the stomach should be dissected at the same distance from the tumour location.

In these carcinomas another aberrant lymphatic pathway can be found. At the inferior aspect of the pancreas there are three or four small unnamed arteries which have connections to the transverse mesocolon (Figure 6).3 As lymph node metastases can be found in this location, it is necessary to dissect the inferior margin of the pancreas in tumours at this location. Positive nodes in this position could be found in 20% of tumours with mesocolic lymph node mestastases.19

In carcinomas of the left colonic (splenic) flexure and the left third of the transverse colon, lymphatic metastasis occurs both to the middle colic artery (arising from the SMA) and to the left colic artery (from the IMA) (Figure 2). Both arteries are divided at their origin; accordingly, the colon then has to be separated below the hepatic flexure on the right side and again within the proximal sigmoid on the left side.

Again aberrant lymphatic spread is observed to the greater omentum, to lymph nodes at the greater curvature of the stomach and to nodes at the inferior aspect of the pancreas (Figure 6). They have to be considered in dissection. The left part of the greater omentum has to be removed together with the tumour. It can be divided about 10 cm to the right side of the tumour-bearing bowel segment. Like the omental resection, the greater curvature of the stomach is dissected.

Carcinomas of the descending colon can metastasize along the left colic artery and the sigmoid arteries towards the IMA (Figure 2). Therefore, a so-called left hemicolectomy has to be performed with a central dissection of the IMA at its origin at the aorta. The colon is divided at the level of the left colic flexure cranially and in the upper third of the rectum caudally (Figure 9).

FIGURE 9

Left hemicolectomy (from Weber K, Perrakis A, Hohenberger W. Standard therapy in colon carcinoma [in German]. Chir Praxis 2010; 72:25–3516).

HMJ-9-3-10-fig9.jpg

In sigmoid carcinomas, lymph node metastases can be found along the sigmoid arteries towards the IMA (Figure 2). In a so-called sigmoid resection, the IMA is divided centrally and the colon is separated within the descending colon on one side and in the upper third of the rectum on the other side (Figures 10 and 11).

FIGURE 10

Sigmoid resection (from Weber K, Perrakis A, Hohenberger W. Standard therapy in colon carcinoma [in German]. Chir Praxis 2010; 72:25–3516).

HMJ-9-3-10-fig10.jpg
FIGURE 11

Situs after mobilization of the entire left colon for sigmoid carcinoma. Intact mesocolic fascial layers and central dissection of the IMA.

HMJ-9-3-10-fig11.jpg

Carcinomas of the distal sigmoid and the rectosigmoid junction are treated like tumours of the upper third of the rectum.21 As lymph node metastases do not occur more than 3 cm below the inferior margin of carcinomas in the mesorectum,22 it is sufficient to separate rectum and mesorectum at a distance of 5 cm below the inferior tumour margin without coning (the 5 cm rule).

Conclusion

Complete mesocolic excision for colon cancer is a specimen-orientated technique of surgery. Preparation for it is performed in embryological planes by sharp dissection. The mesocolic fasciae can be preserved in this way. By central dissection of the supplying arteries, one can remove as many lymph nodes as possible. The aim is to avoid any intraoperative tumour spread and to obtain a complete mesocolic compartment with intact fascial layers containing potential tumour deposits. In addition, extramesocolic lymph node stations are considered depending on the tumour site.

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Perrakis A, Weber K, Merkel S, et al. Lymph node metastasis of carcinomas of transverse colon including flexures: consideration of the extramesocolic lymph node stations. Int J Colorectal Dis 2014; 29:1223–9. http://dx.doi.org/10.1007/s00384-014-1971-2

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Williams NS. The rationale for preservation of the anal sphincter in patients with low rectal cancer. Br J Surg 1984; 71:575–81. http://dx.doi.org/10.1002/bjs.1800710802




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