Colonoscopy


Colonoscopy or coloscopy is a medical procedure involving the endoscopic examination of the large bowel and the distal portion of the small bowel. This examination is performed using either a CCD camera or a fiber optic camera, which is mounted on a flexible tube and passed through the anus.
The purpose of a colonoscopy is to provide a visual diagnosis via inspection of the internal lining of the colon wall, which may include identifying issues such as ulceration or precancerous polyps, and to enable the opportunity for biopsy or the removal of suspected colorectal cancer lesions.
Colonoscopy is similar to sigmoidoscopy, but surveys the entire colon rather than only the sigmoid colon. A colonoscopy permits a comprehensive examination of the entire colon, which is typically around 1,200 to 1,500 millimeters in length.
In contrast, a sigmoidoscopy allows for the examination of only the distal portion of the colon, which spans approximately 600 millimeters. This distinction is medically significant because the benefits of colonoscopy in terms of improving cancer survival have primarily been associated with the detection of lesions in the distal portion of the colon.
Routine use of colonoscopy screening varies globally. In the US, colonoscopy is a commonly recommended and widely utilized screening method for colorectal cancer, often beginning at age 45 or 50, depending on risk factors and guidelines from organizations like the American Cancer Society. However, screening practices differ worldwide. For example, in the European Union, several countries primarily employ fecal occult blood testing or sigmoidoscopy for population-based screening. These variations stem from differences in healthcare systems, policies, and cultural factors. Recent studies have stressed the need for screening strategies and awareness campaigns to combat colorectal cancer - on a global scale.

Medical uses

Conditions that call for colonoscopies include gastrointestinal hemorrhage, unexplained changes in bowel habit and suspicion of malignancy. Colonoscopies are often used to diagnose colon polyp and colon cancer, but are also frequently used to diagnose inflammatory bowel disease.
Fecal occult blood is a quick test which can be done to test for microscopic traces of blood in the stool. A positive test is almost always an indication to do a colonoscopy. In most cases the positive result is just due to hemorrhoids; however, it can also be due to diverticulosis, inflammatory bowel disease, colon cancer, or polyps. Colonic polypectomy has become a routine part of colonoscopy, allowing quick and simple removal of polyps during the procedure, without invasive surgery.
With regard to blood in the stool either visible or occult, it is worthy of note, that occasional rectal bleeding may have multiple non-serious potential causes.

Colon cancer screening

Colonoscopy is one of the colorectal cancer screening tests available to people in the US who are 45 years of age and older. The other screening tests include flexible sigmoidoscopy, double-contrast barium enema, computed tomographic colonography, guaiac-based fecal occult blood test, fecal immunochemical test, and multitarget stool DNA screening test.
Subsequent rescreenings are then scheduled based on the initial results found, with a five- or ten-year recall being common for colonoscopies that produce normal results.
Among people who have had an initial colonoscopy that found no polyps, the risk of developing colorectal cancer within five years is extremely low. Therefore, there is no need for those people to have another colonoscopy sooner than five years after the first screening.
Some medical societies in the US recommend a screening colonoscopy every ten years beginning at age 50 for adults without increased risk for colorectal cancer. Research shows that the risk of cancer is low for 10 years if a high-quality colonoscopy does not detect cancer, so tests for this purpose are indicated every ten years.
Colonoscopy screening is associated with approximately two-thirds fewer deaths due to colorectal cancers on the left side of the colon, and is not associated with a significant reduction in deaths from right-sided disease. It is speculated that colonoscopy might reduce rates of death from colon cancer by detecting some colon polyps and cancers on the left side of the colon early enough that they may be treated, and a smaller number on the right side.
Since polyps often take 10 to 15 years to transform into cancer in someone at average risk of colorectal cancer, guidelines recommend 10 years after a normal screening colonoscopy before the next colonoscopy.
The large randomized pragmatic clinical trial NordICC was the first published trial on the use of colonoscopy as a screening test to prevent colorectal cancer, related death, and death from any cause. It included 84,585 healthy men and women aged 55 to 64 years in Poland, Norway, and Sweden, who were randomized to either receive an invitation to undergo a single screening colonoscopy or to receive no invitation or screening. Of the 28,220 people in the invited group, 11,843 underwent screening. A total of 15 people who underwent colonoscopy had major bleeding after polyp removal.
None of the participants experienced a colon perforation due to colonoscopy. After 10 years, an intention-to-screen analysis showed a significant relative risk reduction of 18% in the risk of colorectal cancer. The analysis showed no significant change in the risk of death from colorectal cancer or in the risk of death from any cause. To prevent one case of colorectal cancer, 455 invitations to colonoscopy were required.
As of 2023, the CONFIRM trial, a randomized trial evaluating colonoscopy vs. fecal immunochemical test is currently ongoing.
In 2021, the US spent $43 billion on cancer screening to prevent five cancers, with colonoscopies accounting for 55% of the total. The death rate from colon cancer has been on a linear decline for 40 years, falling by nearly 50 percent from the 1980s to 2024; however, the increase in screening did not accelerate the decline. Therefore, resources devoted to cancer screening would be better directed toward ensuring widespread access to effective cancer treatment.

Recommendations

The American Cancer Society issues recommendations on colorectal cancer screening guidelines. These guidelines often change and are updated as new studies and technologies have become available
Many other national organizations also issue such guidance, such as the UK's NHS and various European agencies, guidance can vary between such agencies.

Medicare coverage

In the United States, Medicare insurance covers a number of colorectal-cancer screening tests.

Procedural risks

The American Society for Gastrointestinal Endoscopy estimates around three in 1,000 colonoscopies lead to serious complications.

Perforation

The most serious complication is generally gastrointestinal perforation, which is life-threatening and requires immediate surgical intervention.

Issues from general anesthesia

As with any procedure involving anesthesia, complications can occur, such as:
  • allergic reactions,
  • cardiovascular issues,
  • paradoxical agitation,
  • aspiration,
  • dental injury.

    Colon preparation electrolyte issues

Electrolyte imbalance caused by bowel preparation solutions is possible, but current bowel cleansing laxatives are formulated to account for electrolyte balance, making this a very rare event.

Other

During colonoscopies, when a polyp is removed, the risk of complication increases. One of the most serious complications is postpolypectomy coagulation syndrome, occurring in 1 in procedures. It results from a burn injury to the wall of the colon causing abdominal pain, fever, elevated white blood cell count and elevated serum C-reactive protein. Treatment consists of intravenous fluids, antibiotics, and avoiding oral intake of food, water, etc. until symptoms improve. Risk factors include right colon polypectomy, large polyp size, non-polypoid lesions, and hypertension.
Although rare, infections of the colon are a potential colonoscopy risk. The colon is not a sterile environment, and infections can occur during biopsies from what is essentially a 'small shallow cut', enabling bacterial intrusion into lower parts of the colon wall. In cases where the lining of the colon is perforated, bacteria can infiltrate the abdominal cavity.
Minor colonoscopy risks may include nausea, vomiting or allergies to the sedatives that may have been used. If medication is given intravenously, the vein may become irritated, or mild phlebitis may occur.

Technique

Preparation

The colon must be free of solid matter for the test to be performed properly. For one to three days, the patient is required to follow a low fiber or clear-liquid-only diet. Examples of clear fluids are apple juice, chicken and/or beef broth or bouillon, lemon-lime soda, lemonade, sports drink, and water. It is important that the patient remains hydrated. Sports drinks contain electrolytes which are depleted during the purging of the bowel. Drinks containing fiber such as prune and orange juice should not be consumed, nor should liquids dyed red, purple, orange, or sometimes brown; however, cola is allowed. In most cases, tea or coffee taken without milk are allowed.
The day before the colonoscopy, the patient is either given a laxative preparation and large quantities of fluid, or whole bowel irrigation is performed using a solution of polyethylene glycol and electrolytes.
The patient may be asked not to take aspirin or similar products such as salicylate, ibuprofen, etc. for up to ten days before the procedure to avoid the risk of bleeding if a polypectomy is performed during the procedure. A blood test may be performed before the procedure.