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Colonoscopy and flexible sigmoidoscopy 

Colonoscopy and flexible sigmoidoscopy

Colonoscopy and flexible sigmoidoscopy

James E. East

and Brian P. Saunders


July 30, 2015: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.


Preparation of instruments—modified to include discussion of prion disease.

Prophylaxis against endocarditis—modified to reflect updated guidelines.

Flexible sigmoidoscopy—discussion of findings of recent population-based screening studies.

Cost-effectiveness—discussion of importance of quality assurance of endoscopists.

Images—videos of diagnostic colonoscopy and resection of a colonic polyp.

Updated on 28 Nov 2012. The previous version of this content can be found here.
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date: 24 April 2017

Colonoscopy and flexible sigmoidoscopy are techniques for visualizing the lumen of the large bowel. In expert hands, after appropriate explanation to the patient (which increases the chances of the procedure being well tolerated), bowel preparation, and (usually) some form of ‘conscious sedation’, then total colonoscopy is possible in 98 to 99% of cases in the absence of obstruction, a severely ulcerated colon, or other contraindication.

The indications for colonoscopy are wide and constantly expanding, and are likely to continue to do so until alternative less invasive techniques (‘virtual colonoscopy’ or genetic tests) are perfected. Common indications include patients with or requiring: (1) bleeding, anaemia, or occult blood loss; (2) chronic diarrhoea or known inflammatory bowel disease, which is accurately and easily assessed by endoscopy and biopsy; (3) polyps that can be removed endoscopically; (4) surveillance for cancer prevention. Abnormalities found by other diagnostic methods frequently turn out to be spurious when checked colonoscopically. Findings such as anastomotic strictures, typically after Crohn’s resection, are usually easily and effectively dilated by the endoscopist using a ‘through the scope’ balloon.

Flexible sigmoidoscopy is the best means of examining the bowel proximal to the rectosigmoid junction (the distal rectum and anal canal are well seen with a rigid instrument).

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