Fig. 4.1
Division of relevant pedicles in relation to tumour location in the right colon. (a) Right colic artery arising from the superior mesenteric artery. (b) Right colic artery arising from the ileocolic trunk. (c) Right colic artery arising from the middle colic artery. (d) Right colic artery absent. SMA superior mesenteric artery, RCA right colic artery, MCA middle colic artery, RMCA right branch of middle colic artery, LMCA left branch of middle colic artery
Alternatively, as division of the appropriate vessel is crucial, extracorporeal division may be preferable once the colon has been mobilised, if the anatomy is uncertain.
The middle colic artery usually originates from the SMA at the inferior border of the uncinate process of the pancreas. In 25 % it can be absent and in 10 % there may be an accessory or double vessel. The right and left branches of this artery arise at the middle of the transverse colon. If intracorporeal division of the right branch is contemplated, then search for it should begin from the middle of the transverse colon.
The inferior mesenteric artery (IMA) provides the blood supply to the descending and sigmoid colons and upper rectum. It originates from the anterior surface of the abdominal aorta although its position is not constant, lying anywhere along a line from the origin of the SMA to the aortic bifurcation. In most cases, the origin is just below or under the third part of the duodenum. From here the artery runs obliquely and crosses the pelvic brim at the aortic bifurcation. To prevent early injury, the first incision used to commence medial to lateral dissection should be made at the root of the sigmoid mesentery anterior to the right common iliac artery, rather than over the sacral promontory. The left ureter and gonadal vessels pass close to the IMA origin. They must be recognised and dissected clear (if necessary) before the IMA is divided. The diameter of the IMA is 50 % that of the SMA. The principles that apply to division of arterial vessels with modern energy sources and stapling devices are equally relevant to this vessel. Rarely does the IMA have to be divided at its origin. The left colic artery provides a significant blood supply to the splenic flexure. It is important to know the anatomical variations of the LCA as if this is inadvertently divided; there is a risk that this section of the colon will become ischaemic necessitating splenic flexure mobilisation and more proximal division of colon. In over 50 % of individuals, the LCA arises as a separate branch of the IMA, and in the remainder it forms a common trunk with the first sigmoidal artery (Fig. 4.2). A useful tip in identifying the LCA is to locate the IMV as the former usually travels adjacent to the latter.
Fig. 4.2
Anatomical variation of left colic artery. IMA inferior mesenteric artery, LCA left colic artery, SA sigmoidal artery, CT common trunk
4.2.1.1 Other Vascular Injuries
Injury to the common iliac arteries and external and internal iliac veins is possible, either as a trocar injury or during medial to lateral mobilisation of the left colon and total mesorectal excision of the rectum (TME). Blood loss can be significant and this can have an impact on anastomotic integrity (see below). Repair can be achieved laparoscopically, but conversion to an open procedure and specialist vascular intervention is desirable for patient safety.
4.2.2 Ischaemia
Ischaemia of either the proximal or distal parts of an anastomosis will usually result in anastomotic dehiscence. Ischaemia insufficient to cause necrosis may later present with stricture but this is unusual. With a standardised approach to segmental colorectal resection, ischaemia is unusual but may result when there is anatomical variation of the colonic vasculature as previously discussed or probably most commonly during left-sided resection when insufficient mobilisation of the splenic flexure causes the surgeon to divide the left colon too distally in an ischaemic segment. This is most likely in cases with poor marginal artery perfusion. Mostly ischaemia of the proximal conduit can be avoided by fully mobilising the splenic flexure when necessary so that a tension-free anastomosis can be constructed using a well-vascularised bowel. Mostly ischaemia is evident from the colour of the bowel when exteriorised. There may even be a clear demarcation. A tip to ensure that the bowel is well vascularised is to always divide the marginal vessel extracorporeally. Once the level of planned division is identified, the marginal artery is divided between clips. The distal end is tied and the proximal end then gently released to observe arterial blood flow. If there is no active bleeding, then a more proximal site should be chosen. When the bowel itself is divided, there should be bright red mucosal bleeding. There may be a role for the use of Indocyanine Green (ICG) fluorescence to assess perfusion if the technology is available.
Increased blood flow to the colorectal or colo-anal anastomosis may be achieved in the following ways.
1.
A more proximal division of the left colon following full mobilisation of the splenic flexure.
2.
Preserve the ascending left colic artery where possible.
3.
Create a side to end anastomosis.
When balancing the requirement to mobilise the splenic flexure to obtain length with preserving the ascending left colic artery, it is often feasible to divide the inferior mesenteric vein high at the lower border of the pancreas but leave the ascending colic artery intact.
4.2.3 Organ Injury
This section discusses the organs and structures most likely to be injured during a laparoscopic colorectal resection. It includes a discussion on splenic, pancreatic and gastric injury during splenic flexure mobilisation, ureteric injury during left-sided resections and total mesorectal excision and bladder trauma.
4.2.3.1 Spleen, Pancreas and Stomach
Splenic flexure mobilisation is often necessary for anterior resection of the rectum or even for more proximal segmental resection. The aim being to achieve a tension-free and well-vascularised anastomosis of healthy bowel. To assess adequate length, the planned point of colonic division can be brought down to the transected rectum intracorporeally prior to exteriorisation. Extracorporeally the end of the colonic conduit should reach well past the symphysis pubis following resection of the pathological segment in order to reach the pelvic floor comfortably when replaced intracorporeally for anastomosis.
Splenic injury seems to be much less common during laparoscopic surgery than in open surgery. This is because most splenic injuries are a result of traction of the colon, which avulses splenic capsule tissue at the site of congenital adhesion. At open surgery, too much traction can be created and the sites of adhesion are not well seen. Nevertheless, the same problem can occur at laparoscopic surgery, or direct trauma can occur in inexperienced surgeons especially in fat patients with fatty omentum obscuring the natural planes between spleen, omentum and transverse colon. The operator should be aware of potential injury to the spleen, short gastric vessels and pancreas. Excessive colonic retraction can cause bleeding from a tear in the splenic capsule. It can go unrecognised and so should be investigated when blood is noticed pooling in the left upper quadrant. The most likely site for a tear is at the inferior border or hilum. Primary suture repair and/or application of modern haemostatic agents such as fibrin glue or cellular polymer and radiofrequency ablation with pressure should be considered before contemplating a splenectomy [1]. Very effective haemostatic materials are available which are effective even in significant splenic injury, and all abdominal surgeons should be trained in the correct use of these materials. Inappropriate traction on the stomach may result in trauma to the short gastric vessels. During splenic flexure mobilisation, the stomach does not need to be retracted and so should be avoided. There may be times when the lesser sac needs to be entered between the transverse mesocolon and body of pancreas. If this is attempted, strict adherence to the surgical plane between the transverse mesocolon and pancreas is advised. Noting the slight subtle colour difference between pancreatic fat and that of the mesocolon should help guide the dissection.
4.2.3.2 The Ureter and Gonadal Vessels
An understanding of embryology is the key to ensuring that injury to the ureter and gonadal vessels is avoided. During development the abdominal musculature encloses the peritoneal “balloon”. Situated behind the balloon are the pancreas, kidneys, adrenal glands, the great vessels and abdominal musculature (e.g. psoas, quadratus lumborum). The gastrointestinal bud enters the abdominal cavity at the neck of the balloon and takes with it a lining of peritoneum—the visceral peritoneum. It exits at the pelvic brim and continues on at the mid rectum. Within the abdominal cavity, ascending, descending and sigmoid colonic visceral peritoneum is very closely apposed to the posterior parietal peritoneum. During medial to lateral dissection, these two layers can be separated, and by staying in the correct plane, the ureter and gonadal vessels remain behind the posterior parietal peritoneum. The ureter can be identified by its vermiculation.
The left ureter can be juxtaposed to the origin of the IMA and may be retracted upwards when lifting this vessel. Consequently before dividing the IMA, it is vital to ensure that the ureter is clearly separated.
Ureteric trauma is possible during pelvic dissection for a ventral rectopexy, deep infiltrating endometriosis or rectal resection. There are slight anatomical variations in the course of the pelvic part of the ureter between males and females. Appreciation of these differences helps towards protecting the ureters. After crossing the pelvic brim at the origin of the external iliac artery, the ureters travel along the pelvic sidewall anterior to the internal iliac vessels. At the ischial spine, they turn medially and enter the bladder base above the pelvic floor. In the male, the ureters are crossed by the ductus deferens. During low rectal mobilisation, keeping the dissection below the seminal vesicles will avoid ureteric injury, as it is at this point that they enter the bladder base. In the female, the ureters are “hidden” beneath the broad ligament and then lie on the surface of the lateral cervical ligaments before entering the bladder base in front of the vaginal fornix. Unfamiliarity of their course can result in ureteric division or obstruction by applying a haemostatic clip for bleeding, for example. Stenting of the ureter can be useful to help identify its course and also protect it against injury. However, this procedure is for the most part unnecessary except in a few key situations.
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