WE all know about pap smears, mammograms and prostate exams — which are important screening tests to detect early stage cervical, breast and prostate cancers, respectively.

The thinking behind doing these tests regularly is that early detection leads to cure of an otherwise fatal disease. The same can be said about colon cancer. It is the second-highest cause of cancer deaths in most developed countries and the third commonest cancer in both males and females in Jamaica.

Colorectal cancer (CRC) is preventable for the most part. The majority of cancers arise from benign polyps in the colon. It takes about 10 years for an advanced cancer to develop from one of these polyps.

Screening your colon would lead to a significant reduction in death caused by colorectal carcinoma.

Screening for colorectal cancer

Screening for CRC is divided into two risk categories: high risk and average risk.

Patients at high risk include:

• Those with a personal history of adenomatous polyps and CRC;

• Those with a first-degree relative with CRC, especially if the tumour developed below 60 years of age;

• Those with a family history of familial polyposis coli and non-polyposis colon cancer;

• Those with colitis due to inflammatory bowel disease.

The objective of screening is to detect and treat precursor lesions and early stage cancer. The tests available include: feacal occult blood testing (FOBT), flexible sigmoidoscopy (F/S), barium enema, computed tomography colonography (CTC), and colonoscopy.

Patients at high risk for CRC should have interval evaluation of the colon preferably by colonoscopy. This group of individuals is responsible for 25 per cent of new cases of CRC.

People without any of the listed risk factors are at average risk. In these people the risk of developing colon cancer increases with age, particularly after 50 years. Seventy-five per cent of CRC occurs in average- risk patients.

If patients without risk factors account for such a large percentage of patients, then it simply means that everyone above the age of 50 should be screened.

The gold standard is colonoscopy. The procedure is not without its challenges, however, not the least of which includes the fact that it is an invasive test necessitating anaesthesia, with small risk of perforation and failure due to redundant loops of bowel.

Barium enema examination

The radiologist is able to offer two non-invasive tests for screening evaluation of the colon. They are barium enemas and CT colography or virtual colonoscopy.

The double barium enema examination has existed in one form or another since the 1920s, but improved dramatically in the 1960s. The test employs a barium contrast which is instilled via the rectum through a specially designed enema tube tip or foley catheter and is allowed to run through the entire colon by gravity.

The patient is placed in a number of positions while lying on an X-ray table to aid the passage of the barium column through the colon. Once the column of barium has flowed through the colon, reversing the positions previously employed to facilitate forward flow drains excess out. The aim is to obtain a thin coat of barium on the surface of the colon. Air or CO2 is then pumped into the colon, again via the rectum, to distend the loops of colon.

The patient must be prepared, both physically and mentally, to undergo a barium enema examination. Physical preparation involves elimination of feacal residue through a combination of laxatives and low-residue diet for three days preceding the test.

The following regime is successfully used at Imaging and Intervention Associates to obtain a clean colon: Let us assume the patient is booked to do the barium examination on Friday. For three days before the exam (that is Monday, Tuesday and Wednesday) the patient eats only the following:

Breakfast: One boiled egg, two slices of white bread, tea or coffee. Take two dulcolax tablets.

Lunch: Steamed fish or steamed chicken, boiled irish potato or steamed white rice. Take two dulcolax tablets.

Dinner: Soup including irish potato, pumpkin, chicken, and cho-cho. Take one tablespoon of castor oil.

Do not eat yam, dumplings, raw or steamed vegetables, red meat, cereals, cheese, milk, ice cream, peas or beans on any of those days before the exam.

On the day before the exam, that is Thursday: Have no solid foods, liquids only (water, juice, black tea or coffee, or broth)

• At 1:00 pm take four dulcolax tablets and 1 pack of Epsom salts dissolved in eight ounces of water;

• Between 7:00 pm and 8:00 pm, take one pack of Epsom salts dissolved in eight ounces of water;

• Drink one glass of water.

On the day of the exam, that is Friday, have only water, juice, tea, or coffee.

After the exam, drink plenty fluids and go back to a normal diet.

The barium enema examination lasts approximately 30 to 45 minutes. The result is images of the colon which are quite sensitive for the detection of polyps larger than one cm, masses, abnormal narrowing of the colon, diverticula, and abnormalities of the mucosa (lining) of the colon.

The over couch film and spot film images demonstrate advanced cancers in symptomatic patients. While there are no large-scale scientific trials which look at the effect of barium enema on reducing CRC mortality, the goal of screening to maximise the identification of high-risk patients while minimising expense and morbidity (complications of the exam) should be remembered and barium enema achieves this task.

From as far back as 1999, Medicare recognised barium enema as an acceptable screening test for both low- and high-risk patients.

Virtual colonoscopy

CT colonography (CTC) also called virtual colonoscopy is a low-dose CT technique which allows the colon to be imaged in 10-15 minutes. There is no sedation. There is no need for IV contrast and the patient is able to return to his or her normal activities as soon as the test is completed.

Continued advances in computer manipulation of CT images as well as improvements in the CT machines themselves have rendered CTC at least as effective as traditional colonoscopy at detecting polyps larger than six mm in size. The procedure requires the same bowel preparation as barium enemas, as the presence of stool in the colon may cause a false positive result.

Virtual colonoscopy is a safe procedure, but it is not without risk. Some of the risks and disadvantages include:

• During virtual colonoscopy, a small, short tube is placed into your rectum so that carbon dioxide can be pumped into your colon. This inflates your colon so that polyps or other growths are more easily seen. Pumping air into the colon carries a very small risk that it may cause a rupture. But the risk is thought to be much less than with conventional colonoscopy.

• Because polyps or suspicious growths cannot be removed or biopsied during virtual colonoscopy, you may still need to have a conventional colonoscopy if large polyps or other suspicious areas are detected.

• Virtual colonoscopy can miss some polyps that may turn into cancer if they are smaller than 10 mm. (Some of these may or may not be detectable by conventional colonoscopy.)

• Unlike most other screening tests, virtual colonoscopy uses X-rays to create pictures of the colon and rectum. Radiation received during virtual colonoscopy is small, but it could be dangerous for pregnant women. If you are or could be pregnant, you should discuss this risk with your health care provider before the procedure.

There may be other risks, depending on your specific medical condition. Be sure to discuss any concerns with your health care provider before the procedure. The overall risk is much less than conventional colonoscopy and the speed, affordability and accuracy of the test cannot be disputed.

The intention of this article is to promote screening for colorectal cancer, which is a potentially avoidable disease. There are many scientific discussions as to the best screening method. Those discussions are beyond the scope of this article. It is generally accepted that optical or traditional colonoscopy is the gold standard for CRC screening. Your radiologist, however, offers acceptable, effective, non-invasive methods, which are particularly useful for screening the average risk population, which includes you and me.

Dr Duane Chambers is a consultant radiologist and founding partner of Imaging and Intervention Associates located at shops 58 and 59 Kingston Mall, 8 Ocean Boulevard. He may be contacted through the office numbers 618-4346 or 967-7748.