1. What is Colon cancer?

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Colon cancer is a disease that affects the large bowel (also known as the colon), which is part of the digestive system. Cancer can be defined as the uncontrolled growth of abnormal cells. These abnormal cells are often grouped together in tumors. The cells can destroy normal, healthy tissue and can affect the way an organ functions. Colon cancer is the second leading cause of cancer deaths in the United States. It is widely accepted that virtually all cases of colon cancer begin as small growths—called polyps—on the wall of the large bowel. Polyps may contain malignant cancer cells. Over the course of several years, such cancerous polyps may grow in size and invade the wall of the large bowel, forming an invasive tumor. Once the tumor invades the normal barriers between the tissue of the wall and other tissues, it can shed cells into blood or lymphatic vessels. These cells can be carried to other parts of the body in the blood stream or lymph system, and a new tumor may begin to grow elsewhere. This movement of cancer cells is called “metastasis.” Colon cancer will often spread to the liver first. By the time a new tumor is present in another location, the cancer is generally in an advanced stage and usually cannot be cured by surgery alone.

2. Am I at risk of getting colon cancer?

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For a long time, patients were told that a high-fat, high-protein, low-fiber diet was the main risk factor for developing colon cancer. But recent research has provided some more specific information. It is now known that men are slightly more likely to develop colon cancer than women. Colon cancer is also more common in people over the age of fifty years. That is why it is recommended that men over the age of 50 be screened regularly for colon cancer; women over the age of 50 should be screened as well. People who have relatives with colon cancer are at higher risk for developing colon cancer themselves.

3. What should I do to prevent colon cancer?

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Although it is not entirely clear how a person’s diet may contribute to the development of colon cancer, a balanced diet, rich in fibers, is recommended. Studies have shown that people who eat a balanced diet are less likely to develop colon cancer as well as other diseases, such as heart disease. There is also a simple screening test that is used to detect colon cancer early. Most colon cancers tend to bleed, so doctors can analyze stool samples for traces of blood. It is recommended that both men and women over the age of 50 and persons with a family history of colon cancer have their family physician perform this test each year. If blood is found, the doctor will recommend additional tests. Sometimes, cancer is found by these additional tests. In most cases, however, traces of blood are not caused by cancer at all. Instead, additional testing reveals a different, usually benign, reason for the presence of blood, such as hemorrhoids.

4. Should I get a colonoscopy?

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Conventional colonoscopy is a test that allows a physician to inspect the bowel wall for colon cancer and for polyps that could grow into colon cancer. It is commonly recommended to patients when traces of blood are found in a stool sample, but there is no obvious reason for the bleeding. Men over the age of 50 and persons with a family history of colon cancer should consider having this test done every five years to screen for colon cancer. It is important to detect this disease early. As it progresses to more advanced stages, colon cancer becomes more difficult or even impossible to cure. Before the procedure, the bowels must be completely emptied. The patient is asked to drink a specially formulated liquid containing laxatives. A light sedative is usually given at the time of the procedure. The drug is injected into a vein in the arm vein. Then, a colonoscope—a long, flexible tube with a light and a camera at one end—is inserted into anus and advanced into the large bowel. The light and camera allow the doctor to see the bowel wall on a monitor. The colonoscope is also equipped with a small instrument for collecting tissue samples. If a polyp or other lesion is detected, a tissue sample can be taken. The tissue samples can then be examined under a microscope to determine if cancer cells are present. In fact, some polyps can be entirely removed by this technique. Conventional colonoscopy is usually well tolerated. Complications, typically consisting in a tear of the large bowel requiring surgery, are rarely observed.

5. What is a CT Colonoscopy ("Virtual Colonoscopy") and should I get it?

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CT colonoscopy is a new technique for inspecting the wall of the colon; it is still under investigation and is not yet considered to be a standard screening test. Like conventional colonoscopy, CT colonoscopy can be used to detect colon cancer and polyps early. In CT colonoscopy, also called “virtual colonoscopy,” no colonoscope is inserted during the procedure. Generally, no sedation is needed, either. There is also no risk of tearing the bowel wall. The entire examination is based on images taken from the outside with a computed tomography (CT) scanner. (Computed tomography is also known as computed axial tomography, or “CAT scanning.”) The CT scanner consists of the patient couch and an open ring, on which advanced x-ray equipment is mounted. Similar to conventional colonoscopy, the bowels must be completely emptied before the procedure. So, the patient is still required to drink a specially formulated liquid containing laxatives. During the procedure, the patient is positioned on the couch. A short tube is inserted into the anus and the large bowel is distended—inflated—with non-toxic gas, such as carbon dioxide. A substance called “glucagon” may be injected into a vein in the arm. Glucagon relaxes the bowel and suppresses bowel motion, which could blur the images. The couch is then moved into position within the ring, and the ring rotates around the patient. As the ring is rotating, the special x-ray cameras take cross-sectional images of the colon from all directions. The patient will be asked to turn over during the procedure, so that images can be acquired while the patient is lying on the back as well as on the stomach. In our institution, only cutting-edge CT scanners are used for the purpose of CT colonoscopy. These state-of-the-art scanners acquire high-resolution images in the shortest possible length of time. The image data are then analyzed by computers that construct a 3D simulation of the bowel. The results look very similar to what the doctor would see when conducting a conventional colonoscopy procedure. Studies have shown that the accuracy of this technique is sufficient to detect even very small polyps and early cancers. If no lesions or polyps are found on CT colonoscopy, it is reasonable to assume that no malignant tumor (cancer) is present. If lesions are found, however, it is highly recommended that such patients undergo conventional colonoscopy as the next step for obtaining a tissue sample of the lesion in question. CT colonoscopy may be considered as a less invasive first-line alternative to conventional colonoscopy in persons who do not tolerate or who do not wish to undergo conventional colonoscopy.

Common Questions and Answers About CT Colonoscopy

Q: Can you tell me if CT colonsocopy will detect: As much as conventional colonoscopy? Less than conventional colonoscopy? More than conventional colonoscopy? I would prefer CT scan over an intrusive procedure that may cause distress to my GI tract. Can you give me concrete information to help me decide how to spend my healthcare dollars?

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Studies show that CT colonoscopy will detect almost all lesions (such as polyps) in the colon that are larger than 1 cm. In comparison, the doctor will generally detect lesions larger than 5 mm on conventional colonoscopy. Therefore, if no lesions are found in your colon on a good quality CT colonoscopy, it is extremely unlikely that you have colon cancer. In addition to being non-invasive, CT is also more robust than conventional colonoscopy. Conventional colonoscopy shows only the inner surface of the colon. On your CT images, the radiologist can see the inner surface of your colon AND all of the surrounding organs. In evaluating these surrounding organs, the radiologist may find other, unsuspected disease that would not have been seen on conventional colonoscopy.