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Colon
Colon screening may be done in several ways. Screening exams are powerful tools to detect colorectal cancer.
Colon screening may be done in several ways. Screening exams are powerful tools to detect colorectal cancer. Regular screenings enable physicians to detect cancer early. They can also identify and remove polyps and growths of tissue on the lining of the colon or rectum that can potentially become cancerous.
- A colonoscope is a long, slender, flexible tube about the thickness of a finger that has a camera at the tip, enabling doctors to examine the entire colon.
- It is inserted into the body through the anus and gently guided through the rectum and colon. Patients are administered sedatives during the exam to keep them comfortable and relaxed. The test is usually done in the hospital as an outpatient procedure.
- The colonoscope provides the doctor with magnified images of the inner wall of the colon and rectum. If a polyp is found during the examination, instruments can be passed through the colonoscope to remove polyps or tissue samples.
- The extracted tissue samples will be checked for the presence of cancer cells.
- Some patients may be eligible for a virtual colonoscopy, which uses advanced computed tomography (CT) technology and computer software to produce images of the colon.
- A sigmoidoscope is a slender, flexible tube about the thickness of a finger that has a camera at the tip.
- It is inserted into the lower part of the colon through the rectum.
- The sigmoidoscope provides doctors with a view of the inner wall of the rectum and lower colon, allowing them to search for polyps or cancerous tissue.
- The tube is about 2 feet long, so doctors can examine half of the colon. The test is performed in the physician’s office and can be uncomfortable but is generally not painful.
Imaging exams
- If screening exams suggest the presence of cancer, advanced imaging techniques, such as ultrasound, magnetic resonance imaging (MRI), positron emission tomography (PET) and computed tomography (CT) scans, are used to determine if cancer has spread to other organs and tissues.
Double-contrast barium enema
- Before taking an X-ray image, the colon is filled with air and a white, chalky liquid called barium.
- The barium and air show an outline of the colon, rectum and any polyps or abnormal tissue on the X-ray.
Apart from these tests, a fecal occult blood test (FOBT) is recommended by doctors to screen for colon cancer. FOBT is a test to check stool (solid waste) for blood that is detected with a microscope. A small sample of stool is collected in a sterile container and sent to the doctor or laboratory for testing. There are three types of FOBTs:
- Guaiac FOBT: The sample of stool is placed on the special card and is usually tested with a chemical. If there is blood in the stool, the special card changes its color.
- Immunochemical FOBT: A liquid is added to the stool sample. This mixture is injected into a machine that contains antibodies that can detect blood in the stool. If there is blood in the stool, a line appears on the screen of the machine. This test is also called the fecal immunochemical test or FIT.
- Cologuard: Cologuard is a new screening method that combines a FIT test with a deoxyribonucleic acid (DNA) laboratory test. This detects existing colon cancer or advanced precancerous polyps cells. These cells are present on the lining of the large intestine and are shed periodically and passed through the stool. If there are cancerous polyps in the large intestine, cells from these polyps are also shed and can be detected in the stool. Cologuard identifies the DNA associated with colon cancer in these shed cells as well as the presence of blood, which is an early sign of colon cancer in the stool.