Colorectal Cancer Diagnosis and Imaging Tests
Imaging tests used to help diagnose colorectal cancer include the following:
- Chest x-ray (used to detect cancer that has metastasized [spread] to the lungs)
- CT scan (computerized tomography) (used to detect metastasis to lymph nodes, liver, or lungs)
- Double-contrast barium enema (used to detect tumors throughout the colon)
- Flexible sigmoidoscopy (used to detect tumors in the sigmoid colon and the rectum)
- Total colonoscopy (used to detect tumors throughout the colon)
In double-contrast barium enema, air and a contrast solution (barium) are introduced into the large intestine and a fluoroscope is used to produce real-time images of the size, shape, and movement of the colon and rectum.
Patients must refrain from eating or drinking anything after midnight on the day of the procedure. They also are given a laxative and a cleansing enema before the procedure to make sure that the colon is empty.
Double-contrast barium enema results in an accurate diagnosis in about 90 percent of cases. It is less effective in patients with severe diverticulosis (i.e., condition in which many small pouches in the colon bulge outward).
Flexible sigmoidoscopy allows the physician to look for early signs of colorectal cancer (e.g., bleeding, polyps) in the lining of the sigmoid colon and rectum. In this test, a flexible tube containing a light and a camera (called a sigmoidoscope) is inserted through the anus into the rectum and sigmoid colon. The sigmoidoscope is used to transmit images to a monitor. If suspicious tissue is found, the physician inserts special instruments through the tube to remove a sample for examination under a microscope (called biopsy).
Patients must adhere to a liquid diet for 12–24 hours before undergoing sigmoidoscopy to ensure that the colon is empty. The procedure usually takes 10 to 20 minutes and complications (e.g., bleeding, puncture of the colon) are rare.
Total colonoscopy allows the physician to view images of the entire colon and rectum using a long flexible tube with a light and camera (called a colonoscope). Biopsy of suspicious tissue can be performed using instruments inserted through the tube.
Colonoscopy patients must adhere to a liquid diet for 1–3 days before the procedure to ensure that the colon is completely empty. Patients are given a sedative and pain reliever before undergoing the procedure.
Colonoscopy usually takes 30 to 60 minutes and complications (e.g., bleeding, puncture of the colon) are rare. Medication or a probe (e.g., laser, heat, electric) can be inserted through the colonoscope to stop the bleeding if necessary.
Some studies have shown that colonoscopy may identify colorectal cancer and colorectal polyps more effectively than a newer, less invasive procedure called capsule endoscopy. In this diagnostic test, patients swallow a tiny capsule with a double-sided video camera and the colon is examined as the capsule travels through the digestive tract. However, capsule endoscopy may be an alternative in patients who are unable to undergo colonoscopy and research regarding this method of colon cancer diagnosis is ongoing.