 Blog updatesSite updatesContent provided by Jon Lund Clinical Associate Professor, School of Graduate Entry Medicine & Health, University of Nottingham |
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Operations for colorectal cancer Principles: 1. The cancer has to be removed completely without damage to surrounding structures 2. Lymph nodes draining the cancer have to be removed for staging and regional control of disease 3. Lymph nodes run with the arteries supplying the affected part of the bowel and therefore to remove the lymph nodes the arteries are divided as close to their origin as possible whist avoiding devascularisation of remaining bowel e.g. if a tumour is in the caecum the ileocolic artery needs to be divided. Any of these operations may be performed laparoscopically or by open operation Complications Complications of colectomy can include:Early - bleeding Intermediate - chest/wound infection, DVT/PE, anastamotic leak (may be fatal in up to 40%) Late - anastamotic stricture, adhesions In figures 1-6 below the red crosses indicate where arterial divisions are made. The red lines indicate where the bowel is divided. The bowel is joined back together in all operations except for the APER (abdominoperineal excision of rectum), where the tumour is very low in the rectum or in the anal canal, and so cannot be removed without removing the anal sphincters. In this case the sphincters are removed with the tumour, the perineum sewn up and the proximal end of the bowel made into an end colostomy. In low anterior resection a temporary de-functioning colostomy or ileostomy is often formed. Blood Supply to the colon The artery of the midgut (2nd part of duodenum to 2/3 across transverse colon) is the superior mesenteric artery (SMA). Therefore the right colon and up to 2/3 across transverse colon is supplied by branches of the SMA (ileocolic, right colic (where present) and middle colic. The artery of the hindgut (2/3 across transverse colon to dentate line) is the inferior mesentetic artery (IMA). Therefore the left colon, rectum and upper anal canal are supplied by branches of the IMA (left colic, sigmoid arteries and superior rectal). The middle rectal artery is present only infrequently. The inferior rectal artery supplies the anal canal and is a branch of the internal pudendal. Lymphatic vessels and nodes run next to the arteries (see above) 
Key for figures below: IC = ileocolic artery RC = right colic artery (only present in 10-15%) MC = middle colic artery LC = left colic artery IMA = inferior mesenteric artery SR = superior rectal artery (continuation of the IMA once the sigmoid branches have been given off) Right hemicolectomy (fig 1): Indications:
Vessels divided are the ileocolic and right colic a (only present in a minority of people) Fig 1: 
If the tumour involves the hepatic flexure or proximal transverse colon then the right branch of the middle colic artery is also divided to make sure draining lymph nodes are harvested (fig 2). Fig 2 
When tumours are situated at the splenic flexure or in the transverse colon (rare), an extended right hemicolectomy is performed (fig 3). The small bowel is anastamosed to the descending colon. Joining small bowel to colon has a lower chance of leak than joining colon to colon. The vessels divided are ileocolic, middle colic and left colic. Fig 3. 
Left Hemicolectomy For tumours of the sigmoid colon the artery supplying them is the artery of the hindgut, the inferior mesenteric artery, and therefore this has to be divided to remove lymph nodes draining tumours in the descending colon and distally (fig 4). Colon is joined to colon for the anastamosis (small bowel is not used for the join as to remove so much colon would lead to more diarrhoea and frequency of stool than is normally desirable). Resection of the sigmoid colon for diverticular disease is also sometimes perfomed. As this is not an operation for cancer the sigmoid branches of the IMA can be divided closer to the bowel, and the operation is known as a sigmoid colectomy rather than a left hemicolectomy. Fig 4. 
Anterior Resection For tumours of the rectum (up to 15cm from the anal verge), an anterior resection is performed (fig 5). The lymph nodes travel with the IMA so it is this which needs to be divided. Lymph nodes also are within the mesorectum (the mesentery of the rectum, packed behind the rectum in the pelvis). It is very important that the rectal dissection occurs to include all mesorectal tissue (in what’s known as the mesorectal plane). If tumours are in the upper rectum then colon is joined onto midrectum (5cm distally to the lower edge of the tumour) for the anastamosis. If the tumour is in the mid or lower rectum all of the rectum is removed (total mesorectal excision or TME) and the colon joined to the top of the anus for the anastamosis (coloanal anastamosis). In coloanal anastamosies or lower colorectal anastamosies the risk of anastamotic leak is high (12-15%). To minimise the chances of this causing serious problems for the patient a defunctioning stoma (loop ileostomy most often but can be loop colostomy) is formed. If a hole does develop in the anastamosis, faeces will not go through it as it is diverted upstream by the stoma. Around 6 weeks after the operation a contrast enema is performed to check radiologically that the anastamosis has healed. If there is no leak on this test the defunctioning stoma can be reversed by a relatively quick and minor operation. Fig 5. 
Abdomino-perineal excision of rectum To perform an anterior resection there has to be at least 1cm of normal rectum distal to the tumour to ensure complete removal of the tumour. In very low rectal tumours or tumours of the anal canal getting this 1cm clearance would mean removing part or all of the anal sphincters. If joined back up this would have a disastrous effect on continence and quality of life and so the sphincters and anus are removed with the tumour and the hole in the perineum stitched up (an abdomino-perineal excision of rectum APER)(fig 6). The colon is then brought out as a permanent end colostomy in the left iliac fossa. Breakdown of the perineal wound is not uncommon especially if the patient has had preoperative radiotherapy (~15-20%). Fig 6: 
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