Colonoscopy is done to screen asymptomatic people for polyps and colorectal cancers and to look for the causes of iron-deficiency anaemia, the passage of blood in the stools, lower abdominal or perineal pain, diarrhoea, constipation and other changes in bowel habit.
We commonly find polyps in the colon and rectum and remove them with a device called a snare that is passed down the biopsy channel of the instrument and submitted to a pathologist for analysis and diagnosis. Most polyps are benign new growths that develop in the mucosa, but, over time, they can transition to colorectal cancer if not removed.
Familial adenomatous polyposis (FAP) is a relatively rare inherited disorder that results in multiple polyps developing in the colon and rectum, from early teenage years with colon cancer usually developing before age 30. People who inherit this abnormality are advised to have a proctocolectomy (removal of the entire colon and rectum) in their teenage years. A proctocolectomy prevents them from dying in their twenties from colorectal cancer. Still, they are also at risk of developing polyps in the duodenum and stomach, so they need to be kept under lifelong endoscopic surveillance.
Patients who have an iron deficiency should be investigated by gastroscopy AND colonoscopy. Most cases of iron deficiency are due to occult or overt bleeding from the gastrointestinal or genitourinary tracts.
Colorectal cancer is very common. If diagnosed early, it usually has quite a good prognosis. Furthermore, colorectal cancers develop from adenomas, which may have a tubular, villous, or serrated growth pattern, so by detecting and removing polyps, the risk of developing colorectal cancer can be significantly reduced. Gastrointestinal societies around the world unanimously recommend screening colonoscopy for everyone when they turn fifty and earlier in those who have a first-degree relative (mother, father, brother or sister). A colonoscopy screening is also recommended for those who have a genetic history of colorectal cancer – first done at an age ten years younger than the age at which the relative with colorectal cancer was diagnosed. If the first colonoscopy does not reveal any polyps, the next colonoscopy should be scheduled for ten years later, provided that no worrisome symptoms develop in the interim. If polyps are found and removed, a repeat colonoscopy should be scheduled for five years later. However, if the polyps are numerous or large or dysplastic, the interval between colonoscopies short be shortened. With a worrying trend of rising numbers of younger adults being diagnosed with colorectal cancer, the American Gastroenterological Society is now starting to advocate for screening to begin at age 40 or 45.
The colon must be cleaned thoroughly in the days preceding the colonoscopy to allow excellent visualisation of the interior of the colon and rectum and terminal ileum (last segment of the small intestine. Colonoscopic cleaning involves taking four Senokot tablets two days before the procedure. The patient must adhere strictly to a clear fluid diet comprised of water, black tea or coffee, clear soup, jelly, pulp-free juice and sports drinks for the twenty-four hours before the colonoscopy. They should also take four sachets of Picoprep during the afternoon before the examination. Patients must avoid drinking liquids that contain dairy products and purple or red dye.
During a colonoscopy procedure, the patient is sedated, and Dr Stapleton carefully guides the flexible instrument into the anus, through the rectum into the colon and distal small bowel, while inflating the bowel with CO2 gas to distend it to get the best possible visualisation. The instrument, which is, essentially, a very sophisticated video camera, transmits images of the inside of the bowel to a monitor in the endoscopy room. The doctor may remove polyps or tissue for biopsy during the colonoscopy.
Patients will have to wait about an hour while the sedative wears off and may experience bloating as a result of the gas the doctor placed in the colon during the colonoscopy. Traces of blood in the stool may be seen after polyps have been removed or after biopsies are taken during a colonoscopy. However, if blood clots are passed or severe abdominal pain is experienced, or a high fever develops, there may be a serious complication, and the patient should return to the hospital and contact the colonoscopist.