Colectomy (col- + -ectomy) is bowel resection of the large bowel (colon). It consists of the surgical removal of any extent of the colon, usually segmental resection (partial colectomy). In extreme cases where the entire large intestine is removed, it is called total colectomy, and proctocolectomy (procto- + colectomy) denotes that the rectum is included.
Some of the most common indications for colectomy are:
- Colon cancer
- Diverticulitis and diverticular disease of the large intestine
- Inflammatory bowel disease such as ulcerative colitis or Crohn's disease. Colectomy neither cures nor eliminates Crohn's disease, instead only removing part of the entire diseased large intestine. A colectomy is considered a cure for ulcerative colitis because the disease attacks only the large intestine and therefore will not be able to flare up again if the entire large intestine (cecum, ascending colon, transverse colon, descending colon and sigmoid colon) and rectum are removed. However, it does not always take away extra-intestinal symptoms.
- Prophylactic colectomy can be indicated in some forms of polyposis, Lynch syndrome and certain cases of inflammatory bowel disease because of high risk for development of colorectal cancer.
- Bowel infarction
Traditionally, colectomy is performed via an abdominal incision (laparotomy), though minimally invasive colectomy, by means of laparoscopy, is growing both in scope of indications and popularity, and is a well-established procedure as of 2006[update] in many medical centers. Recent experience has shown the feasibility of single port access colectomy.
Resection of any part of the colon entails mobilization and ligation of the corresponding blood vessels. Lymphadenectomy is usually performed through excision of the fatty tissue adjacent to these vessels (mesocolon), in operations for colon cancer.
When the resection is complete, the surgeon has the option of immediately restoring the bowel, by stitching or stapling together both the cut ends (primary anastomosis), or creating a colostomy. Several factors are taken into account, including:
- Circumstances of the operation (elective vs emergency); In many cases emergency resection of colon with anastomosis needs to be done and this carries a higher complication rate since proper bowel preparation is not possible in emergency situations
- Disease being treated; (i.e., no colectomy surgery can cure Crohn's disease, because the disease usually recurs at the site where the healthy sections of the large intestine were joined together. For example, if a patient with Crohn's disease has a transverse colectomy, their Crohn's will usually reappear at the resection site of the ascending and descending colons.)
- Acute physiological state of the patient;
- Impact of living with a colostomy, albeit temporarily;
- Use of a specific preoperative regimen of low residue diet and laxatives (so-called "bowel prep").
An anastomosis carries the risk of dehiscence (breakdown of the stitches), which can lead to contamination of the peritoneal cavity, peritonitis, sepsis and death. A number of factors may increase the risk of anastomotic dehiscence, either partial ('leak') or complete. Basic surgical principles include ensuring a good blood supply to the opposing ends, and a lack of tension at the join. The use of NSAIDS for analgesia following gastrointestinal surgery remains controversial, given mixed evidence of an increased risk of leakage from any bowel anastomosis created. This risk may vary according to the class of NSAID prescribed. 
Colostomy is always safer, but places a societal, psychological and physical burden on the patient. The choice is by no means an easy one and is rife with controversy, being a frequent topic of heated debate among surgeons all over the world.
- Right hemicolectomy and left hemicolectomy refer to the resection of the ascending colon (right) and the descending colon (left), respectively. When part of the transverse colon is also resected, it may be referred to as an extended hemicolectomy
- Transverse colectomy is also possible, though uncommon.
- Sigmoidectomy is a resection of the sigmoid colon, sometimes including part or all of the rectum (proctosigmoidectomy). When a sigmoidectomy is followed by terminal colostomy and closure of the rectal stump, it is called a Hartmann operation; this is usually done out of impossibility to perform a "double-barrel" or Mikulicz colostomy, which is preferred because it makes "takedown" (reoperation to restore normal intestinal continuity by means of an anastomosis) considerably easier.
- When the entire colon is removed, this is called a total colectomy, also known as Lane's Operation. If the rectum is also removed, it is a total proctocolectomy.
- Subtotal colectomy is resection of part of the colon or a resection of all of the colon without complete resection of the colon.
Today more than 40% of colon resections in United States are performed via laparoscopic approach.
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