Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Basic Principles of the Operative Treatment of Colorectal Cancer
Despite recent advances in understanding the biology of cancer that have resulted in new targeted and biological therapies, surgery is still the primary treatment for most patients with colorectal cancer. While the overall treatment plan may be different for colon and rectal cancers, the principles that guide the surgical procedures to treat them are similar. These principles, based on the Halstedian concept of tumor progression from the primary site to the regional nodes, were first introduced over a century ago. While the ideas about tumor progression have evolved and the concept of orderly tumor progression from the primary site along the lymphatic vessels to progressively more central nodal stations has been challenged, the basic principles of the operative treatment have remained unaltered due to the need to remove a minimum number of nodes for accurate staging. In addition, there is evidence that the excision of the bowel and its mesentery along anatomical planes established during embryologic development is associated with lower risk of local recurrence and improved survival. In this chapter, we will review the basic principles of colorectal resections and the specific technical details for interventions performed to treat tumors located in different segments of the large bowel.
General Principles
Curative-intent surgery for colon and rectal cancers is aimed at removing the tumor-bearing segment of the bowel with adequate margins and excising en bloc the mesentery containing the feeding vessels and regional lymph nodes. The extent of the resection depends on the location of the primary tumor, which determines lymphatic drainage. Lymphatic capillaries are primarily located in the submucosal and subserosal layers of the bowel wall. Lymphatic flow is primarily circumferential in the colon, with longitudinal spread along the bowel wall being generally less than 1 cm in each direction. Therefore, a 5-cm margin of normal bowel on either side of the primary tumor is considered sufficient to avoid anastomotic recurrence. The length of the terminal ileum resected in patients with cecal cancer does not influence the risk of anastomotic recurrence. Since longitudinal lymphatic flow is primarily upward in the rectum, cancer cells do not generally spread distally along the bowel wall more than 1 cm from the macroscopic distal end of the tumor. Therefore, a 2-cm margin of normal bowel distal to the tumor, or an even smaller margin in patients treated with neoadjuvant therapy, is considered appropriate for an oncologically safe resection. This margin may be insufficient in rectal cancer patients with extensive nodal metastasis that could block the lymphatic channels in the bowel wall and the mesorectum and redirect the lymphatic flow distally.
The regional lymph nodes of the colon are classified into four main groups on the basis of their proximity to the bowel and its blood supply: epicolic, paracolic, intermediate, and apical ( Fig. 166.1 ). Epicolic lymph nodes are located in the bowel wall under the peritoneum, often close to the epiploic appendices; paracolic nodes are found along the marginal vessels; intermediate nodes are in the middle of the mesentery; and apical (or central) nodes are located close to the root of the mesentery, in the vicinity of the origin of the named vessels. Although colorectal cancer generally spreads sequentially from paracolic to apical lymph nodes, nodal metastases sometimes skip one of the nodal groups. Therefore an oncologic resection should include all nodal groups.
The application of the principles of the sentinel node used extensively in breast cancer and melanoma surgery remains controversial in colon and rectal cancer surgery. The injection of isosulfan blue or radioactive dye in the periphery of the tumor to identify the apical node was found to improve staging and to modify the extent of the resection in several retrospective case series. These results have not been replicated in prospective trials. Therefore, the principle of sentinel node sampling is rarely used in colon and rectal cancer surgery today.
The extent of mesenteric resection for colon cancer is determined by the need to remove all the lymph nodes draining the corresponding segment of the bowel, including the central lymph nodes. Since in most cases a tumor is located between two named vascular pedicles, both pedicles should be resected at their origin. When central nodes are suspected of being involved by the tumor, they should be marked on the specimen, as they have negative prognostic information. Because lymphatic drainage does not always follow an orderly pattern, lymph nodes located away from the feeding vessels and suspected of tumor involvement should be removed during surgery and analyzed. If metastatic lymph nodes are not removed during surgery, the resection is considered incomplete.
In addition to achieving safe oncologic margins and adequate lymphadenectomy, ensuring sufficient blood supply to the bowel ends and maintaining tension-free anastomosis in order to avoid anastomotic complications are also important goals of surgical resection for colorectal cancer.
A locally advanced tumor attached to adjacent organs should be removed en bloc with the contiguously involved structures. Since inflammatory adhesions cannot be distinguished clinically or radiographically from tumor infiltration, en bloc resection of the affected organ avoids the risk of disseminating cancer cells associated with the separation of structures infiltrated by the tumor. Intraoperative tumor perforation has negative prognostic implications. The relative completeness of the resection (R0, R1, or R2), combining clinical and pathologic information, is important for determining the risk of locoregional recurrence and long-term prognosis.
The no-touch technique, in which the vascular supply is controlled before the tumor is manipulated in order to avoid releasing cancer cells into the bloodstream, has not been shown to improve oncologic outcomes. However, for minimally invasive colorectal surgery, early vascular control with medial-to-lateral dissection of the mesentery, before mobilization of the colon, is the preferred approach because it helps identify all vascular and retroperitoneal structures.
Proper surgical technique is crucial for achieving optimal results. For rectal cancer, a total mesorectal excision (TME) using sharp dissection along normal anatomical planes to remove the rectum along with its mesorectal envelope is associated with a low risk of local tumor recurrence. Likewise, a complete mesocolic excision (CME), with removal of all the lymph node-bearing mesentery along embryologic planes and central ligation of the named blood vessels, has been associated with a low risk of local tumor recurrence in colon cancer patients. A recent study from Denmark showed that, in patients with stage I–III colon adenocarcinoma, CME resulted in longer disease-free survival than conventional resection. Differences in the completeness of TME and CME probably contribute to the variation in oncologic outcomes between surgeons and between institutions.
Localized Colon Cancer
Colectomy
Resection is indicated for biopsy-proven adenocarcinoma of the colon without evidence of distant metastasis and without contraindications to major surgery. The extent of a resection depends on the location of the primary tumor. For tumors in the cecum and ascending colon, a right hemicolectomy is used, with division of the ileocolic, right colic, and sometimes the right branch of the middle colic vessels ( Fig. 166.2A ). The portion of the omentum attached to the removed segment of the colon should be resected en bloc with the colon and mesentery. For tumors located at the hepatic flexure or in the right portion of the transverse colon, an extended right colectomy is used, which in addition to division of the ileocolic and right colic vessels, involves division of the middle colic vessels at their origin ( Fig. 166.2B ). For tumors in the middle portion of the transverse colon, either an extended right colectomy or a transverse colectomy is employed. A transverse colectomy divides only the middle colic vessels, but to ensure a tension-free anastomosis, both the hepatic flexure and the splenic flexure are often mobilized ( Fig. 166.2C ). For tumors in the distal transverse colon, splenic flexure, or proximal descending colon, either an extended right colectomy ( Fig. 166.2D ) or a left hemicolectomy ( Fig. 166.2E ) is used. The latter procedure involves division of the left branches of the middle colic vessels and the left colic artery and vein at the point where the left colic vein joins the inferior mesenteric vein.
Because locally advanced tumors in the transverse colon can metastasize to the regional lymph nodes located along the greater omentum and the gastroepiploic arcades, an omentectomy with division of the gastroepiploic vessels at their origin may be necessary for complete nodal control. However, the benefit of such an extended lymphadenectomy is subject to debate.
For tumors in the sigmoid colon, a sigmoid colectomy, including the superior rectal artery and its takeoff from the inferior mesenteric artery, is performed ( Fig. 166.2F ).
Patients with synchronous tumors, which occur in up to 5% of patients with colorectal cancer, should be investigated for hereditary colorectal cancer syndromes or other predisposing conditions. In patients without hereditary predisposition, and depending on the location of the primary tumors, either separate resections or an extended resection incorporating both lesions can be used. When more than one segmental resection is performed, care must be taken to preserve the blood supply to the intermediate segment of colon in order to avoid ischemia and the associated perioperative complications. In patients with hereditary nonpolyposis colorectal cancer, synchronous tumors are indications for a subtotal or total colectomy.
Minimally Invasive Approaches
Several prospective clinical trials have shown that laparoscopic colectomy for cancer is associated with short-term advantages and leads to equivalent long-term oncologic outcomes compared with the traditional open surgical approach. The advantages of laparoscopic surgery include less postoperative pain, earlier return of bowel function, shorter hospital stay, and decreased rate of complications. However, laparoscopic surgery is technically challenging and takes time to master. In addition, the presence of multiple adhesions from previous surgery, locally advanced disease, or obesity may make laparoscopy particularly difficult. Early or preemptive conversion from laparoscopic to open surgery is associated with complication rates similar to those for open surgery, but complications are more frequent for late (reactive) conversion.
Laparoscopic colectomy is typically performed using three to five ports and a specimen extraction site. With growing expertise, fewer ports, smaller instruments, and shorter incisions are now being used. Thus, in single-port laparoscopic surgery (SPLS), performed through a small port at the specimen extraction site, the camera and the operating ports are all positioned through the SPLS device.
A recent systematic review of 38 case series, including 565 patients who underwent SPLS, found that the procedure is feasible but technically challenging. Evidence regarding the safety of SPLS was limited. After comparing the results of that review with the results from a Cochrane Review of 3526 patients treated with conventional laparoscopic colectomy, the authors concluded that SPLS did not result in less postoperative pain or a shorter hospital stay than conventional laparoscopic surgery.
Robotic platforms have further enhanced the visualization and dexterity available to the surgeon. Compared with conventional laparoscopy, robotic colon resection is associated with lower conversion rates and similar short-term outcomes but higher costs.
Anastomotic Techniques
After a colon resection, bowel continuity can be reestablished using different techniques, but a few common surgical principles must be followed. The ends to be anastomosed—small bowel, colon, or rectum—should have an intact blood supply. The terminal ileum, like the rest of the small bowel, has a plexiform rich blood supply. The colon has a more segmental blood supply provided by the vasa recta branching individually from the marginal arcade. Ideally, the last segmental artery of the segment of the colon to anastomose should have an intact arterial pulse. The end of the bowel to anastomose should be mobilized enough to allow a tension-free anastomosis. Finally, the stitches or staples should include the submucosa of the bowel, the layer with the highest collagen content and the most important layer for holding the ends of the bowel together. The description of the individual anastomotic techniques is beyond the scope of this chapter. Handsewn and stapled anastomoses are associated with similar complication rates in the normal bowel. However, the handsewn techniques may be preferred for suturing thick, edematous, or fibrotic bowel.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here