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1 From the Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St, Philadelphia, PA 19104 (M.S.L., S.E.R., I.L.); and Department of Radiology, Hahnemann University Hospital, Philadelphia, Pa (S.N.G.). Received July 13, 2001; accepted July 16.
Index terms: Editorials • Cancer screening, 75.31, 75.32 • Colon, radiography, 75.12 • Colon neoplasms, 75.31, 75.32
The case for colorectal cancer screening is based on the concept that most colorectal cancers develop from preexisting adenomatous polyps that gradually transform over a period of years into invasive adenocarcinomas by means of an adenoma-carcinoma sequence (1). It should be possible, therefore, to prevent most deaths due to colorectal cancer by detecting and removing adenomatous polyps that have not yet undergone malignant degeneration or that have transformed into early cancers.
Because colorectal neoplasms are more common in older people, screening for colorectal cancer has been advocated for average-risk persons beginning at the age of 50 years. In the past, fecal occult blood tests and sigmoidoscopy were the primary methods recommended for colorectal cancer screening. However, more than one-third of adenomatous polyps are located proximal to the splenic flexure of the colon (2), and these polyps are inaccessible to sigmoidoscopy, which depicts only the distal colon and rectum. As pointed out by others, the use of sigmoidoscopy as a major screening tool for colorectal cancer is thus no more logical than the performance of mammography of one breast to screen women for breast cancer (3).
Because of the potential for increased detection of polyps and early cancers on visually based studies of the entire colon, the American Cancer Society and other medical organizations have endorsed a new set of clinical guidelines for colorectal cancer screening that includes a total colon examination—either a double-contrast barium enema examination every 5 years or colonoscopy every 10 years (4). The double-contrast barium enema examination has also been approved as a reimbursable option for colorectal cancer screening both for average-risk and for high-risk individuals under recent Medicare guidelines (5). The rationale for the use of the screening barium enema examination is supported by cost-effectiveness models that have shown that a double-contrast barium enema examination at 5-year intervals is competitive with other strategies for colorectal cancer screening (6–8).
In view of current screening recommendations for colorectal cancer, we believe that radiologists have a public health responsibility to provide screening barium enema examinations as a service to the general population. Currently, however, only a small percentage of eligible individuals undergo any form of screening for colorectal cancer. Reasons for poor compliance range from fear of the screening procedure itself to inadequate understanding of the importance of screening and inconsistent implementation of screening guidelines by health care providers. The medical community, therefore, must engage in a concerted and sustained effort to ensure that most average-risk individuals aged 50 years or older undergo screening for colorectal cancer. If this initiative is successful, however, there are not enough physicians in any one specialty to meet the demands for screening on such a massive scale. We already are aware of long waiting times for colonoscopy at centers where such screening examinations are performed. An array of tests (including sigmoidoscopy, colonoscopy, and double-contrast barium enema) must, therefore, be provided by a coalition of primary care practitioners and specialists who share the common goal of preventing colorectal cancer through widespread screening.
It should be pointed out that some members of the gastroenterologic community advocate colonoscopy rather than double-contrast barium enema examinations as the primary tool for colorectal cancer screening (3). In the gastroenterologic literature, however, the reported rate of incomplete colonoscopic examinations has ranged from 4% to 25% (2,9–11). In such cases, the barium enema examination remains an important complementary examination for evaluation of the proximal portion of the colon not visualized at colonoscopy. Thus, paradoxically, increased utilization of colonoscopy as the primary tool for colorectal cancer screening also should lead to an increased number of barium enema examinations performed as follow-up tests after incomplete colonoscopy. There also are patients at greater risk for complications from colonoscopy in whom the double-contrast barium enema examination is the preferred examination. The complementary nature of these procedures underscores the need for a true partnership between gastroenterologists and radiologists if this initiative for colorectal cancer screening is to be successful.
Despite evidence that the double-contrast barium enema examination could have an instrumental role in colorectal cancer screening, some investigators remain skeptical about the value of the screening barium enema examination for helping to detect polyps. In a highly publicized study by Winawer et al (12) in the New England Journal of Medicine, double-contrast barium enema examinations helped detect fewer than 50% of polyps larger than 1 cm that were found at colonoscopy. In an accompanying editorial entitled "The End of Barium Enemas?", Fletcher (13) concluded that the double-contrast barium enema examination should no longer be considered an acceptable procedure for surveillance in patients at increased risk for colonic polyps or for diagnostic evaluation of the colon. On further analysis, however, this study consisted of a total of only 23 patients with polyps larger than 1 cm (12). Is it reasonable to draw conclusions about the effectiveness of a procedure on the basis of such a small number of cases? We do not think so. In other well-designed studies with strict radiologic-endoscopic correlation, the double-contrast barium enema examination has been shown to have a sensitivity of 71% for polyps larger than 7 mm (14) and a sensitivity of 81% for polyps larger than 1 cm (15). These data suggest that the results of the study by Winawer et al are not representative of the true capabilities of the double-contrast barium enema examination. Use of sensitivity statistics from a one-time screening examination also ignores the potential for subsequent detection of early lesions on repeat screening studies.
Despite a growing consensus among medical and governmental organizations about the need for colorectal cancer screening and the importance of a total colon examination for effective screening, the radiologic community itself has failed to embrace the double-contrast barium enema examination as a screening tool for colorectal cancer. Why are so many radiologists unenthusiastic about performing double-contrast barium enema examinations or promoting this technique for colorectal cancer screening? Differences between the double-contrast barium enema and cross-sectional imaging studies such as computed tomography (CT) and magnetic resonance (MR) imaging may be partly responsible. These "high-tech" imaging studies are more glamorous than conventional barium studies and are performed by technologists. Moreover, they generate substantial revenue because of the high relative value units, or RVUs, assigned to these procedures. Conversely, double-contrast barium enema examinations are usually performed by radiologists wearing heavy lead aprons, and these studies generate less revenue because of their lower RVUs. As a result, double-contrast barium enema examinations are labor-intensive procedures with a low reimbursement in relation to that of other imaging studies. The end result is inadequate utilization of a potentially valuable screening procedure.
How can this be changed? If the double-contrast barium enema examination is ever to be a viable option for colorectal cancer screening, it must be performed in a rapid and efficient way that does not compromise the heavy workloads and busy schedules of today’s radiologic practices. This means radiologists should be able to complete most screening barium enema examinations using less than 5 minutes of fluoroscopy time and 20–30 minutes of room time. Fortunately, most screening candidates are relatively healthy, mobile individuals in whom a screening barium enema examination is much less arduous than it is in sick or debilitated patients. As radiologists become more proficient with the fluoroscopic portion of these screening studies, it should be possible to limit the acquisition of overhead radiographs to those views not obtainable at fluoroscopy (eg, left and right lateral decubitus views and a prone angled view of the rectosigmoid). Radiologists could also be interpreting other types of studies while the overhead radiographs are being obtained. Finally, the time needed to review the double-contrast images should decrease considerably as radiologists gain experience in interpreting these studies.
The development and refinement of digital gastrointestinal imaging has additional implications for colorectal cancer screening. It is well documented that the use of digital fluoroscopy results in a faster examination with decreased fluoroscopy and room times and more rapid patient throughput (16). When the fluoroscopic spot images are interpreted at workstations integrated into a picture archiving and communications system, or PACS, without the generation of hard copies of the images, the long-term costs of these digital imaging systems also are lower because of the lower cost of storing images electronically (16). Thus, digital imaging has the potential to make these screening barium enema examinations more efficient and economical than ever before.
Digital imaging systems also allow radiologists immediate access to the images from double-contrast barium enema studies obtained at remote sites (17). As a result, screening examinations performed by other less experienced radiologists or by residents can be monitored and reviewed at integrated workstations. In a study from England (18), it was shown that technologists can also be trained to perform adequate double-contrast barium enema examinations, the results of which subsequently are reviewed and interpreted by radiologists. In another study (19), it was found that the sensitivity of technologist-performed double-contrast barium enema studies for polyps and cancers was comparable to that of double-contrast barium enema studies performed by radiologists. It is possible, therefore, to envision a new breed of technologists specifically trained to perform large numbers of screening barium enema examinations with digital equipment at outpatient centers around the country in a setting analogous to that of cytotechnologists who perform Papanicolaou smears to screen for cervical cancer. Radiologists at remote sites (including other sites in the same facility) could interpret these studies at electronically linked workstations and render an immediate interpretation of the images or, if necessary, suggest the acquisition of additional views to help clarify questionable findings. Such an approach would allow radiologists to be involved in radiologic screening for colorectal cancer in a way that makes optimal use of their time and expertise.
Another factor that discourages radiologists from performing these screening barium enema examinations is lack of formal training in double-contrast gastrointestinal radiology. It is therefore important for radiologists to become more adept at performing double-contrast barium enema examinations and more proficient and confident at interpreting the images from these studies. At first, this might seem like a formidable task, but if radiologists can acquire the skills needed to interpret sophisticated MR studies obtained with complex imaging sequences, there is no reason they cannot acquire, or in some cases reacquire, the skills needed to master the technical and interpretive aspects of double-contrast barium enema studies. A host of resources are available to facilitate this process, including textbooks, review articles, course syllabi, videotapes, workshops, refresher courses, and even 1-week mini-fellowships. Radiologists therefore have at their disposal the means for learning to perform and interpret high-quality double-contrast barium enema studies for colorectal cancer screening. It is particularly important to maintain high standards for this examination if we are to achieve acceptable levels of accuracy for the detection of colorectal polyps and cancers.
In recent years, CT colonography has emerged as an exciting new-generation technique that uses volumetric CT data and specialized imaging software for demonstrating colorectal neoplasms (20). Preliminary data from populations with high disease prevalence suggest that CT colonography may be as sensitive or even more sensitive than the double-contrast barium enema examination for demonstrating polyps larger than 1 cm (20). As with the evolution of other new imaging technologies, however, such enthusiasm must be tempered by other reports in which the results have been less positive (21–23). Although CT colonography is a promising technique with enormous potential for colorectal cancer screening, concerns about reimbursement issues and diagnostic interpretation times (experts have reported average interpretation times as long as 30 minutes) (24) must also be resolved before CT colonography becomes an effective clinical tool for screening. Thus, for the present, we believe that the double-contrast barium enema examination remains the most feasible radiologic test for colorectal cancer screening.
Ultimately, successful radiologic screening for colorectal cancer requires not only the interest and skill of radiologists but also a location and environment (including equipment and personnel) conducive to screening in healthy outpatients on a widespread basis. In the end, radiologists should recognize that performance of the screening barium enema examination provides an invaluable public service by helping to lower the mortality rate due to colorectal cancer. Thus, it is in the interest not only of the radiologic community but also of society for the barium enema examination to have a more prominent role in screening for colorectal cancer. Indeed, we believe the answer is a resounding "no" to the question raised in the recent editorial ("The End of Barium Enemas?") in the New England Journal of Medicine (13). As far as the double-contrast barium enema examination is concerned, the words of Mark Twain seem particularly apt: "The report of my death is exaggerated" (25).
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