Colorectal Cancer Screening: What’s Accurate and Cost-Effective?
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Expires November 30, 2014
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Because colorectal cancer is often asymptomatic, routine screening is essential to detect lesions at an early stage. The evolution of health care has brought new and improved screening methods for colorectal cancer, including CT colonography. This article weighs the pros and cons of the available screening methods used to detect colorectal cancer in the general population today.
BARIUM ENEMA
Procedure
The BE, also known as a lower GI series, was the first screening test to allow the clinician to identify polyps or masses as outlined by barium sulfate.3 This test requires the patient to lie in an oblique position on his/her left side while barium sulfate (known as single-contrast BE, or SCBE), sometimes followed by air (known as double-contrast BE, or DCBE), is flowed through a tube inserted into the rectum. As the colon fills, the radiologist takes multiple overhead x-ray images. The patient is then required to roll on the table several times, causing the barium to coat the entire mucosa of the colon and rectum, which allows for visualization from various angles (see Figure 1).11
Patient Experience
Screening with the BE has some disadvantages to the patient. Patients may experience discomfort at multiple points: during the instillation of gas and barium into the colon, during the maintenance of the gas and barium levels, and during the maneuvering and holding positions of the procedure itself.2 Some patients, interviewed after a BE was performed, indicated feeling embarrassed during the procedure.6 Although the ability to evaluate images during the exam allows the radiologist to share preliminary results with the patient, the immediate disclosure of bad news is deemed somewhat inappropriate. If the procedure reveals positive findings, the radiologist must be sure to speak with the patient in a private area after the procedure. The patient is in a vulnerable state while in the exam room, and the exam room staff may not be adequately equipped to handle the emotional impact, properly address patient questions, or provide counseling.2,6
Advantages and Disadvantages
Few studies are now being done on the advantages and disadvantages of performing a BE compared to a colonoscopy or CTC—most likely due to the belief that colonoscopy is the better choice. BEs are considered to be one of the safer of the direct screening tests for CRC because sedation is not required and, compared to colonoscopy, the rate of colon perforation is lower (0.02% to 0.04% for BE versus 0.016% to 0.2% for colonoscopy).12,13
In a small study of 15 asymptomatic men age 71, it was found that BEs have a lower sensitivity for detecting CRC as compared with colonoscopy or CTC.2 Sensitivity for lesions ≥ 10 mm is only 48% and for lesions ≥ 6 mm is only 35%, proving the BE to be a highly ineffective screening test for CRC (see Table 1).3
In a randomized study of 5,025 symptomatic patients with abnormal bowel movements and/or abdominal pain, BE has a detection rate of only 5% compared to the much higher sensitivity of CTC or colonoscopy.14
A third study calls attention to the risks associated with the DCBE exam, noting that it is less invasive and less dangerous than colonoscopy, as it does not require sedation and poses less risk for perforation of the lining of the colon.15 The study authors concluded that DCBE has a high sensitivity for clinically significant neoplasms (> 6 mm) but not for small polyps, which may be captured with other tests. DCBE may also supplement incomplete colonoscopy to rule out obstruction.
However, because of the loss of biopsy capabilities, further testing is required when abnormalities are found during the DCBE, diminishing the potential cost effectiveness of the exam. The study authors suggested that DCBEs may be used to screen those who are asymptomatic and seem to have minimal risk factors.15
Limitations
Limitations to successful BE screening include patient compliance and test result interpretation skills. With interpretation skills declining due to limited training of professionals to read BEs, results are becoming less accurate, and the test itself can be seen as less reliable. BEs are less popular, and therefore skills in reading the films are becoming outdated.2 If BE screening is to be used as the primary direct screening tool for CRC, it is imperative that radiologists and gastroenterology physicians and clinicians be well trained in this GI procedure.
Also, patients undergoing BE absorb about 15 mGy of radiation per procedure, versus 0.01 mGy to 0.15 mGy absorbed with a typical chest x-ray.16 For patients with a history of increased radiation exposure or if radiation exposure is a major concern of the patient, BE may not be an appropriate first choice.
On the next page: Colonoscopy >>
