Colorectal cancersurgery

Introduction

Surgery is the mainstay of curative therapy for colorectal cancer. There is considerable controversy about who should perform this surgery— general or colorectal surgeons. Currently there is no clear answer, but surgeons working regularly in the pelvis may get better results in rectal cancer.

Curative resection requires the excision of the primary tumour and its lymphatic drainage with an enveloping margin of normal tissue.

Pre-operative preparation

The precise site and local extent of the tumour should be known before laparotomy; knowledge of distant spread is helpful. Full colonoscopy or proctosigmoidoscopy and air-contrast barium enema (in the absence of obstruction or perforation) is required. The liver is imaged with CT and/or ultrasound examination; CT and endo-anal ultrasound imaging of the pelvis may offer additional information of the depth of invasion of rectal cancers. Additional decisions are required before surgery for rectal cancer:

♦ Should transanal local excision be considered?

♦ If radical surgery is contemplated, should/can the sphincters be spared?

♦ If a stoma is planned the stoma care team must meet with the patient and plan the site of the stoma with attention to belt lines and skin creases.

♦ In choosing the operative approach, especially in rectal cancer, functional consequences are of prime importance—will the patient be able to cope with a colostomy or the different bowel habit associated with altered anatomy consequent on avoiding a colostomy?

Peri-operative antibiotics and thrombo-embolic prophylaxis are mandatory.

Principles in primary resection

The local anatomy of the disease and signs of distant spread are sought, perhaps using intra-operative ultrasound liver scan. The extent of resection is defined and the appropriate segment mobilized, including the arteries and veins associated with its lymphatic drainage, dividing these at their origins. The bowel segment and its lymphatic field are excised intact. If an anastomosis is planned, it is fashioned without tension, ensuring a good lumen and secure apposition. Minimally invasive colon cancer surgery is still unproven.

Rectal cancer

The rectum is mobilized circumferentially by sharp dissection in the plane outside the mesorectal fascial envelope, either to 3 cm below the tumour if part of the rectum is being preserved, or to the pelvic floor if a coloanal anastomosis or abdomino-perineal resection (APER) are planned.

If performing an anastomosis with anal observation, the meso-rectum is divided and after cross-stapling the bowel, the specimen is removed and an anastomosis made, either hand-sutured or by transanal circular stapling. If an APER is planned, an oval incision is made around the anus; the ischiorectal fat and pelvic floor muscles are incised to allow the specimen to be delivered intact through the perineum. Total excision of the mesorectum is considered essential.

Local excision

Around 5% of rectal cancers may be removed by non-radical transanal surgery. This is particularly appropriate in small, low, well-differentiated cancers on the posterior wall, especially if the patient is not an ideal candidate for major abdominal surgery.

Via a Parks' anal retractor, a disc of rectal wall is marked with a 1 cm margin around the tumour. Diathermy is used to cut through the full thickness of the rectal wall, taking a sliver of extra-rectal fat. The specimen should be pinned on cork to orientate it for the pathologist. The rectal defect may be closed if possible. If the pathologist reports incomplete excision, spread through the rectal wall, or poorly differentiated carcinoma, radical surgery may be required to obtain local extirpation of tumour, if the patient is fit.

Some lesions not reachable by the Parks' approach may be locally removable by transanal endoscopic microsurgery (TEM), using a special 4 cm rigid endoscope with binocular vision.

Surgery of recurrent cancer

Local recurrence occurs most commonly in rectal cancer, usually outside the bowel lumen. If investigations suggest that a recurrence is isolated and potentially resectable, further surgery should be considered. Clearance may involve removal of residual rectum and other pelvic organs, including the bladder and/or uterus.

Metastasis confined to one lobe of the liver or less than four in both lobes may warrant resection, as there is up to a 30% chance of cure.

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