Minimally invasive endoscopic examination of the large colon and the distal part of the small bowel with a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy of suspected lesions. Virtual colonoscopy, which uses 3D imagery reconstructed from computed tomography (CAT) scans, is also possible, as a totally non-invasive medical test, although it is not standard and still under investigation.
Colonoscopy is similar but not the same as sigmoidoscopy.
The difference between colonoscopy and sigmoidoscopy is related to which parts of the colon each can examine. Sigmoidoscopy allows doctors to view only the final part of the colon, while colonoscopy allows a complete examination of the colon.
Indications for colonoscopy include gastrointestinal hemorrhage, unexplained changes in bowel habit or suspicion of malignancy. Colonoscopies are often used to diagnose or rule out colon cancer, but are also frequently used to diagnose inflammatory bowel disease.
The days prior to the colonoscopy the patient is given a laxative preparation (such as sodium picosulfate, sodium phosphate solution, or a solution of polyethylene glycol and electrolytes) and large quantities of fluid and a low fibre or clear fluid only diet.
A very small proportion of patients suffer from perforation. This is a medical emergency and may require immediate surgery. Post colonoscopy bleeding and sedation reactions are also possible side effects.