The colon derives embryologically from the midgut and hindgut.
It is divided into the cecum, ascending, transverse, descending and sigmoid colon and rectum.
Arteries, veins and lymphatic drainage are located in the mesocolon, which during the oncological surgical resections of total mesorectal excision and complete mesocolic excision gets removed in its entirety corresponding to the part of the colon to be removed.
The commonest indication for surgical resection of the colon is a colorectal malignancy, and the resection should be carried out according to oncological principles:
Colonic resection is classified as major surgery and should not be undertaken if the patient is physically not fit to sustain a major procedure. Reversible and modifiable risk factors should be addressed before surgery, and postoperatively, a patient may require intensive or high dependency facilities.
Colonic resection can be carried out via open (laparotomy) or minimal access (laparoscopic, robotic) approaches.
Colonic resection requires a full contingent of operating theater personnel (scrub side, anesthesia side, and assistant to position the patient), an anesthetist, and a team of surgeons (at least one operating surgeon and one assistant).
Before surgery, the patient should be thoroughly evaluated.
The key to adequate resection is the blood supply to the colon. Resection for benign disease does not need to be as extensive, but resection for malignancy should aim to resect the named colonic vessels supplying the cancer-bearing portion of the colon as close to their origin as possible to yield an adequate number of lymph nodes in the colonic mesentery (> 12).
The bowel proximal and distal to the resection has to be mobilized to allow a tension-free anastomosis, and the anastomosis should have a good blood supply. Depending on expertise and equipment available, a bowel anastomosis can be performed hand-sewn or stapled.
For example, a formal right hemicolectomy entails ligation of the ileocolic, right colic (if present) and right branch of the middle colic artery. Proximal bowel division is carried out at the terminal ileum, and distal bowel division at the transverse colon. The anastomosis is conventionally formed as a side-to-side between the terminal ileum and the transverse colon.
Resection of a sigmoid colon tumor entails ligation of the inferior mesenteric artery and inferior mesenteric vein. Proximal bowel division is carried out at the distal descending colon, and distal bowel division at the upper rectum, above the peritoneal reflection. The anastomosis is conventionally formed as an end-to-end between the descending colon and the upper rectum with the help of a circular stapling device inserted via the anal canal.
Procedural complications include bleeding, most often venous in nature due to the handling of the mesocolon or during dissection of the greater omentum, and rarely from any of the named vessels.
However, an arterial bleed from the named vessels of the colon can be torrential and requires swift action, especially in laparoscopic procedures, where the bleeding can potentially obscure the view if it hits the camera.
Direct pressure where possible to temporarily arrest the bleeding buys time to strategise, reposition, request additional instruments, site further ports, if necessary, and definitively stop the bleed.
Another intra-operative complication is damage to surrounding structures. The structure most at risk is the left ureter. For left-sided surgery, it should always be identified. If an intra-operative injury (diathermy burn, transection) occurs and is recognised immediately, it can be repaired, and a ureteric stent should be placed to reduce the risk of stricture. If the injury is only diagnosed in the post-operative period, management depends on the extent and location of the injury, the general state of the patient and expertise available. A urological specialist should be consulted if available.
Post-operative complications include infections (wound, chest, urinary tract). Early mobilization, physiotherapy, incentive spirometry and removal of urinary catheters can prevent infections. Wound infection risk in clean-contaminated surgery is greatly reduced by giving prophylactic antibiotics within one hour of skin incision.
Anastomotic leak is a dreaded complication for all surgeons performing colonic resection and primary anastomosis. A high index of suspicion is indicated if postoperatively, a patient does not progress as expected, as signs and symptoms can be subtle to start with, especially if the leak is in the pelvis and the patient has a defunctioning stoma. Patients may have pyrexia, tachycardia, cardiac arrhythmias (new onset atrial fibrillation), complain of abdominal pain and bloating, and have a distended, tender, and potentially peritonitic abdomen. Inflammatory markers will be raised more markedly than expected in the post-operative period. Free air under the diaphragm may not be visible on an erect chest x-ray, but CT will show pneumoperitoneum and fluid around the anastomosis. In patients who have undergone anterior resection, it is advised to perform the scan with rectal contrast.
Depending on the severity of the leak and the patient's general state, the management can include all or parts of the following:
Prerequisites For Good Anastomosis
Adequate length of the colonic conduit for anterior resection:
While colon resection is done by the surgeon, the monitoring of the patient and preoperative workup is usually done by the anesthesiologist. Both before and after surgery, the nurse plays a vital role in bowel preparation and postoperative monitoring. The patient must have DVT prophylaxis and must be taught how to use the incentive spirometer. Physical therapy is usually consulted for ambulation of the patient in the post-operative period. 
Today elective colon resections have excellent outcomes. Most patients have a short stay in hospital of about four days. By paying attention to detail, the risk of wound infection is also minimized. Current data indicate that laparoscopic colectomy is as effective as open colectomy in preventing recurrence of cancer. Further, several clinical trials have shown that the risk of seeding is not increased at the port sites. (Level ll)