Bradley J. Champagne and Thomas J. Edwards

Introduction

Left colectomy is a resection of the colon within the territory supplied by the inferior mesenteric artery. The arterial supply of the colon is divided by the embryologic partitioning between midgut and hindgut, so a left colectomy is a resection of the hindgut, excluding the rectum. Terms such as left hemicolectomy, sigmoid colectomy, and sigmoid wedge resection also apply to left-sided colonic resection. Common indications include neoplasia, ischemia, and diverticulitis.

Surgical Principles

The pattern of left colonic resection is defined by the indication for surgery, the need to facilitate a tension-free colo-colonic anastomosis, and the blood supply. The most common indication for isolated left colonic resection is neoplasia. In this case, a radical lymphadenectomy is necessary for staging and prognosis, and lymphatic drainage must be considered. Because the pattern of lymphatic drainage for the colon follows that of the arterial supply, the inclusion of the mesocolic envelope containing the inferior mesenteric artery (IMA) and its branches, with ligation of the IMA close to its origin, ensures that this is achieved. This is referred to as a high ligation of the IMA. This approach may devascularize the entire left colon, requiring its resection and the mobilization of the distal right colon for anastomosis to the upper rectum.

Other indications for left colonic resection include diverticular disease, ischemia, Crohn disease, sigmoid volvulus, rectal prolapse, and secondary involvement in noncolonic processes, such as ovarian carcinoma. None of these conditions requires high ligation of the IMA, and in these cases it may be acceptable to ligate only the relevant branches of the IMA, perform a less extensive mobilization of the left colon, and create a tension-free anastomosis.

Anatomy for Preoperative Imaging

For colonic carcinoma, computed tomography (CT) of the chest, abdomen, and pelvis provides preoperative staging of the disease. CT includes identification of distant metastases, gross local lymph node involvement, and local invasion of the primary tumor (Fig. 22-1, A). Full colonoscopic evaluation determines the presence of synchronous lesions. For benign disease, CT and colonoscopy may help to identify pathologic features, such as the extent of Crohn disease or ischemia, that may affect approach and extent of dissection.

Surface Anatomy, Incision, and Port Placement

Left colectomy may be performed as either an open or a laparoscopic procedure. For either approach, the patient should be in the Lloyd-Davis position, supine, with the patient’s buttocks at the foot of the table and legs slightly flexed in the horizontal position and held in leg supports. For a laparoscopic approach, the patient is secured with gel pad or bean bag in anticipation of an extreme head-down and right lateral tilt position.

A number of different port configurations have been described; the authors’ preferred approach is shown in Figure 22-1, B. Open left hemicolectomy may be performed through either a midline or a left transverse incision.

Vascular Anatomy

The anatomy of the vascular supply to the colon is demonstrated in Figure 22-2. Knowledge of these vessels, the autonomic nerves, and the lymphatic drainage, as well as its relationship to the spleen, pancreas, kidney, and ureter, is required for successful completion of the left hemicolectomy (Figs 22-3 and 22-4, A).

The arterial blood supply to the left colon is derived from the IMA, which is the most distal of the three midline branches of the abdominal aorta. The ascending left colic or left colic artery is the first branch of the IMA. This supplies the descending colon and the splenic flexure, via the marginal artery of Drummond. The marginal artery joins the middle colic branch of the superior mesenteric artery in the midtransverse colon (see Fig. 22-2, A). The arterial supply to the splenic flexure is subject to a great degree of variability (Fig. 22-4, A). The marginal artery may be augmented by a second arcade, located more proximally in the mesocolon, known as the arc of Riolan. Also, both the marginal artery of Drummond and the arc of Riolan may be absent. Therefore, if the IMA and its branches have been ligated, it is essential to assess the vascularity of the colon at the proximal resection margin intraoperatively to ensure an adequate blood supply to the anastomosis.

Distally, branches of the IMA supply the sigmoid colon and vary greatly in number. The IMA itself proceeds to pass over the pelvic brim and thereby changes its name to the superior rectal artery, at which point it bifurcates and supplies the majority of the rectum.

Venous drainage of the left colon and hindgut is through tributaries of the inferior mesenteric vein (IMV) (see Fig. 22-2, B). The IMV lies in the base of the left mesocolon and passes posterior to the lower border of the pancreas, just lateral to the 4th portion of the duodenum. Under the pancreas, the IMV joins the splenic vein and superior mesenteric vein to form the portal vein. The IMV is significant in colorectal disease because it tethers the left colon, and high ligation is necessary for full left colon mobilization. Division of the IMV 1 inch (2.5 cm) below the inferior border of the pancreas provides several inches of extra mobility, often assisting the creation of a tension-free anastomosis (Fig. 22-4, B and C).

Splenic Flexure

For left colonic resection, the sigmoid and descending colon, splenic flexure, proximal rectum, and distal transverse colon all require mobilization. Although there is no mandatory sequence in which this procedure should be undertaken, the authors usually prefer to commence at the splenic flexure.

Although the splenic flexure is not mobilized routinely by all surgeons, this is an important skill to manage splenic flexure tumors and ischemic bowel and to allow sufficient mobility of the remaining proximal colon to fashion a safe, tension-free anastomosis. The flexure may be mobilized from a medial, lateral, or inferior approach, each of which may be used in laparoscopic or open surgery. Often, successful mobilization requires the use of a combination of approaches, allowing the surgeon to “cone in” to the most inaccessible section of the flexure.

Starting at the midtransverse colon, the greater omentum is elevated superiorly, demonstrating the avascular plane between omentum and transverse colon. At its left lateral extent, the omentum often exhibits adhesions to both the splenic flexure and the capsule of the spleen. Traction on the flexure may cause inadvertent trauma to the spleen. This complication may be mitigated by superior/cephalad retraction of the greater omentum in the midline and commencing dissection in the midtransverse colon. Opening this plane medially provides entry to the lesser sac, identified by visualization of the posterior wall of the stomach, and exposes the superior aspect of the transverse mesocolon (Fig. 22-5, A).

As with the lateral descending and sigmoid mobilization, there is a line of reflection between the parietal and visceral peritoneum. This line is less easy to see than the white line of Toldt but is present nevertheless (Fig. 22-5, B). The peritoneum must again be incised just above this line of reflection (closer to the colon). Mobilization too far from the retroperitoneum (too close to the colon) makes a defect through the mesentery of the colon. While mobilizing, attention must be paid to the jejunum, which is often only a layer of peritoneum away from the area of dissection. Superior mobilization is complete when the colon to the left of the midline is fully freed from its superior attachments.

Full mobilization of the splenic flexure requires division of the IMV. The inferior approach to the splenic flexure uses this as the starting point. With the transverse colon retracted superiorly and the small bowel retracted to the patient’s right, the 4th part of the duodenum and ligament of Treitz are visualized (see Figs. 22-4, B and C, and 22-5, C). This approach exposes the IMV inferior to the vessel passing posterior to the pancreas. Once this has been divided, with Toldt’s fascia identified, mobilization of the proximal descending colon continues from medial to lateral, through the mesocolon to the left lateral side wall. The retroperitoneum, gonadal vessels, and ureter are protected deep to the dissection, and the mesocolon and colon are preserved anteriorly.

Toldt’s fascia continues superiorly, posterior to the body of the pancreas. Therefore, at the inferior border of the pancreas, the surgeon must cease to use this as the plane of dissection and instead release the transverse mesocolon from the anterior surface of the pancreas. This is most readily achieved toward the tail of the pancreas. In doing so, the lesser sac is entered. The lateral attachments are then divided, and the greater omentum is freed from the colon as previously described.

Sigmoid and Descending Colon

The left colon, as a part of the hindgut, originated as a midline structure. Through developmental rotation, however, the left colon has come to reside on the left side of the abdominal cavity, with the descending colon/mesocolon adherent to the parietal peritoneum overlying the retroperitoneum. The junction of parietal peritoneum and retroperitoneum is known as Toldt’s fascia, or the white line of Toldt. Dissection at this junction mobilizes the mesocolon and restores the left colon to the midline.

The sigmoid colon may be mobilized by starting on the medial or lateral side. When the correct planes are defined, Toldt’s fascia is carefully preserved. The left gonadal vessels, left ureter, and para-aortic autonomic nerves are posterior to this layer and should therefore be protected. In open surgery, this is best performed from the lateral aspect, where the “white line of Toldt” indicates the reflection of the parietal and visceral peritoneum. The peritoneum should be incised just above this line. The sigmoid mesocolon is then elevated from the retroperitoneum under slight tension and mobilization continued medially.

The peritoneum is scored proximal and distal to the inferior mesenteric artery. This approach allows the origin of the IMA to be encircled before division (Fig. 22-6), and it is the first step in a laparoscopic medial-to-lateral approach. Having confirmed the plane of dissection and preservation of the ureter in the retroperitoneum, the surgeon continues dissection laterally to the lateral peritoneal attachment.

Rather than aiming for flush ligation at its origin, a 1- to 2-cm length of the IMA should be preserved, to ensure that the superior hypogastric plexus of the autonomic nervous system is not inadvertently damaged where it encircles the IMA (Fig. 22-6). For tumors of the left colon, the IMA should be divided proximal to the takeoff of the left colic artery to ensure a full lymphadenectomy.

Upper Mesorectal Mobilization, Transection, and Anastomosis

Although by definition, no rectum is resected in a left hemicolectomy, it is often necessary to mobilize the proximal rectum to allow the passage of the circular stapling devices for a stapled anastomosis, or to ensure a good blood supply to the distal component of the anastomosis. This approach is covered in detail in Chapter 24.

Once an adequate distal margin has been obtained, the rectum may be transected. The specimen is removed from the field.

If the IMA has been preserved and there is adequate length of distal sigmoid colon, a hand-sewn anastomosis may then be performed. If the distal transection line is at or below the pelvic brim, it is more straightforward to perform a stapled anastomosis.

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