Subspecialty Clinics: Radiology Colorectal Cancer: The Case for Barium Enema
ROBERT L. MacCARTY, M.D., Department ofDiagnostic Radiology
Both colonoscopy and barium enema are important techniques for examining the colon for polyps and cancer. They are approximately equally sensitive in detecting polypoid lesions of 7 to 10 mm or larger. A major limitation of colonoscopy is that the cecum cannot be visualized in 10 to 36% of cases. The comparable accuracy for detecting significant lesions, greater safety, and greater cost-effectiveness of barium enema favor its use in most patients.
The American Cancer Society has estimated that 155,000 new cases of colorectal cancer occurred in the United States in 1990 and that 61,000 Americans died of this disease.' For both men and women, the incidence of colorectal cancer is second only to lung cancer.' Our society invests considerable time, effort, and money for the detection and treatment of premalignant and malignant lesions of the large intestine. Toward this end, the traditional role of barium enema examination has been altered by the introduction and increasing availability of colonoscopy. Recently, because of cost-containment efforts by Medicare and other third-party payers, limitations have been imposed on expenditures for health-care services. These efforts to increase rationing of resources for health care will continue. The optimal use of resources for the detection, treatment, and follow-up of colorectal polyps and cancer necessitates a knowledge of the natural history of these neoplasms and the strengths and limitations of the various available techniques as well as careful analysis of the expected costs and benefits. NATURAL HISTORY AND MORPHOLOGIC FEATURES Overall, the 5-year survival rate for colorectal cancer is 52%. Localized disease is associated with a much better survival rate (84%) than is regional or distant disease (56% and 6%, Address reprint requests to Dr. R. L. MacCarty, Department of Diagnostic Radiology, Mayo Clinic, Rochester, MN 55905. Mayo Clin Proc 67:253-257, 1992
respectively).' Most experts believe that early detection of colorectal cancer substantially increases the patient's chance of survival. Removal of precancerous adenomatous polyps has been shown to decrease the incidence of carcinoma by 85%.2 There is evidence that colonic carcinomas generally evolve from preexisting benign lesions (that is, areas of epithelial dysplasia with or Without frank formation of an adenoma).' Most adenomatous polyps, however, do not become carcinomas; in the ones that do, usually many years elapse before this process occurs. The mean time for malignant transformation has been estimated to be 3.6 years for adenomas associated with severe dysplasia and 18 years for adenomas associated with mild dysplasia.t-' In two studies in which polyps were evaluated for a mean of 5 or more years, more than 50% showed no growth, slightly more than 33% grew, and 14% actually decreased or disappeared completely.6,7 The demonstrated stability of most polyps and the generally long lead time for malignant transformation are reasons for optimism in determining strategies to decrease the incidence of colonic carcinoma and the associated mortality through early detection of malignant and premalignant lesions. The morphologic features of a lesion in the colon are helpful in predicting the likelihood of malignant involvement. Pedunculated lesions are unlikely to harbor a malignant changer" however, if they do, they are much less likely to metastasize than is a sessile lesion of comparable size'? (Fig. I and 2). Histologically, adenomatous polyps are classified as 253
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
Mayo Clin Proc, March 1992,Vol 67
Fig. I. Barium enema examination, depicting l-cm pedunculated adenoma (arrow) in sigmoid colon.
Fig. 2. Barium enema examination, showing l-cm sessile carcinoma (arrow) in sigmoid colon.
tubular, tubulovillous, and villous. The higher the percentage of villous features, the more likely that foci of carcinoma will be encountered (Table I). The exception is the so-called carpet lesion, which does not seem to have the same high malignant potential as a more polypoid villous tumor" (Fig. 3). In general, the diameter of the lesion must be between 1 and 2 em to detect villous features grossly. Features that suggest villous elements within a lesion include innumerable small to tiny fingerlike lobulations and a granular surface pattern. A direct correlation exists between the size of a polypoid lesion and the likelihood of malignant disease. I I Size is the most important variable for assessing malignant potential (Table I). A related important factor is rate of growth, which is usually expressed in terms of doubling time (l doubling
time = 25% increase in diameter). In a recent study, the doubling time for adenomas was 5.83 years, and for carcinomas, it was 2.38 years." Therefore, rapid growth on serial examinations suggests a malignant process (Fig. 4 and 5). Furthermore, a previously demonstrated pedunculated polyp that grows in such a way as to obliterate its pedicle is likely to be a carcinoma.
254
Table I.-Likelihood of Malignant Foci Within Colorectal Adenomas on the Basis of Histologic Type and Size Malignant foci (%) Histologic type
2 cm
Tubular Tubulovillous Villous
1.0 3.9 9.5
10.2 7.4 10.3
34.7 45.8 52.5
Modified from Muto and associates. 11 By permission of J. B. Lippincott Company.
SCREENING FOR COLORECTAL POLYPS AND CANCER Because of the lengthy natural history of premalignant adenomas, colorectal cancer is well suited for screening. Analysis of stool specimens for occult blood has been widely heralded as a first-line screening test to identify a subgroup of patients who might benefit from radiologic or endoscopic assessment. In most cases, however, gastrointestinal blood loss is not due to a colorectal neoplasm. In addition, cancerous lesions tend to bleed intermittently; this factor causes false-negative results of fecal occult blood tests. Because most small adenomas do not bleed, they are unsuitable for screening by such tests." Therefore, even with widespread use of fecal occult blood tests, a large percentage of the population will still be at risk for colorectal adenomas and carcinomas. Whether selected by screening or by case finding, numerous patients are referred for complete colon examinations, and many more could potentially benefit.
Mayo Clio Proc, March 1992, Vol 67
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
255
Fig. 3. Barium enema examination, depicting large carpetlike villous adenoma occupying cecum. Barium fills multiple variegated spaces among innumerable frondlike projections that arise from surface of lesion. (From MacCarty RL: Radiology of the alimentary tract. In Clinical Medicine. Vol 10, Chapter 57. Edited by JA Spittell Jr. Philadelphia, Harper & Row, Publishers, 1986, pp 1-56. By permission of J. B. Lippincott Company.)
Many published articles that purport to show the superiority of colonoscopy in comparison with barium enema examination are flawed for one or more of the following reasons: (I) colonoscopy was used as the "gold standard," and no mechanism was included in the study design to uncover missed diagnoses; (2) high-quality endoscopy was compared with low-quality radiology; (3) usually, colonoscopies were performed after the barium enema examination, and the colonoscopist was not blinded to the results of such previous studies; (4) references to the radiologic literature included old reports (ones published before the availability of modem double contrast techniques). Both single contrast barium enema examination with careful fluoroscopically guided manual compression and stateof-the-art double contrast barium enema examination will detect 80 to 94% of colonic polyps'v'? and 90 to 98% of colonic carcinomas.":" At the Mayo Clinic, our experience is that colonoscopy and barium enema examination are approximately equally sensitive in detecting polypoid lesions of 7 to 10 mm or larger.
Fig. 4. Barium enema examination, disclosing tiny (approximately 2 mm in diameter) benign polyp (arrows) in transverse colon, demonstrated on three examinations during 4 years and showing no change in size. (Metallic 2-cm graduated scale is adjacent to polyp.)
256
Mayo elin Proc, March 1992, Vol 67
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
Fig. 5. A, Initial barium enema examination, revealing sessile polyp (arrow) (approximately 8 mm in diameter) in sigmoid colon. B, Nineteen months later, lesion had grown to a diameter of almost 2 cm. Carcinoma was proved at operation.
Because of the comparable or almost comparable sensitivity ofcolonoscopy and barium enema examination, the greater cost of colonoscopy (at least twice as much as barium enema), and the increased risk of complications (rate of perforation, I in 500 colonoscopies versus I in 5,000 to 10,000 barium enema examinations), the barium enema examination is preferred for the initial evaluation of the entire colon for colorectal neoplasms. A major limitation of colonoscopy is that the cecum cannot be visualized in 10 to 36% of cases. 2 1-24 Because approximately a fourth of the carcinomas occur in the cecum, colonoscopy will fail to detect 25% of cancerous lesions about 20% of the time, even if the sensitivity were 100% in the visualized portions of the colon. The demonstrated and acknowledged superiority of colonoscopy for detecting minute polyps does not justify its use as a screening procedure because the rate of perforation and associated mortality are greater than is the incidence of malignant polyps of 5 mm or smaller. Several studies have shown that barium enema examinations are not only less expensive and safer than colonoscopy but also more cost-effective, even when a higher sensitivity for colonoscopy has been assumed for cost-tobenefit calculations.P'"
MANAGEMENT OF PATIENTS WITH COLORECTALPOLVPS
never harbor malignant disease, and in a considerable percentage of cases, they are hyperplastic rather than adenomatous. When diminutive polyps are discovered during a barium enema examination, they may be safely monitored (Fig. 4); however, when they are found incidentally at endoscopy, they should be removed, if possible. The follow-up and management of patients who have had polyps removed are controversial, and definitive data that support a specific strategy are lacking. A suggested strategy based on the size, number, and histologic features of the index polyps is outlined in Figure 6 and assumes that patients are in either a high-risk or a low-risk category. 29 Both colonoscopy and barium enema examination have roles in such a strategy. The one (albeit substantial) advantage of colonoscopy over barium enema examination is the ability to remove polyps during the procedure. Thus, colonoscopy is a reasonable choice for surveying the colon when polyps have previously been diagnosed and are therefore likely to be encountered again, especially in patients who have had multiple polyps. After all polyps have been removed, however, the costeffectiveness of repeated colonoscopies at frequent intervals diminishes, and the risks become difficult to justify. Survey examinations ofthe colon may then be done by using barium enema at appropriate intervals. The need for clinical trials to test the success of this and other management strategies is obvious.
The ability to predict, by using barium enema examination, the biologic importance of a polypoid lesion on the basis of morphologic features and size has substantial implications in patient management. From a practical standpoint, a I-em or larger polyp, regardless of its morphologic aspects, is potentially cancerous and should be removed for histologic study, unless clinical factors (for example, terminal illness) dictate otherwise. Diminutive polyps (smaller than 5 mm) virtually
Endoscopy and barium enema examination are powerful techniques with complementary strengths and weaknesses. The current state of the science and art of medicine and the current and future medical-economic environment necessitate the judicious use of both procedures to decrease the incidence of colorectal cancer and the associated mortality.
CONCLUSION
BARIUM ENEMAIN DIAGNOSING COLORECTAL CANCER
Mayo Clin Proc, March 1992,Vol67
Solitary index polyp Pedunculated or sessile polyp with tubular histologic features
ROBERT L. MacCARTY, M.D., Department ofDiagnostic Radiology
Both colonoscopy and barium enema are important techniques for examining the colon for polyps and cancer. They are approximately equally sensitive in detecting polypoid lesions of 7 to 10 mm or larger. A major limitation of colonoscopy is that the cecum cannot be visualized in 10 to 36% of cases. The comparable accuracy for detecting significant lesions, greater safety, and greater cost-effectiveness of barium enema favor its use in most patients.
The American Cancer Society has estimated that 155,000 new cases of colorectal cancer occurred in the United States in 1990 and that 61,000 Americans died of this disease.' For both men and women, the incidence of colorectal cancer is second only to lung cancer.' Our society invests considerable time, effort, and money for the detection and treatment of premalignant and malignant lesions of the large intestine. Toward this end, the traditional role of barium enema examination has been altered by the introduction and increasing availability of colonoscopy. Recently, because of cost-containment efforts by Medicare and other third-party payers, limitations have been imposed on expenditures for health-care services. These efforts to increase rationing of resources for health care will continue. The optimal use of resources for the detection, treatment, and follow-up of colorectal polyps and cancer necessitates a knowledge of the natural history of these neoplasms and the strengths and limitations of the various available techniques as well as careful analysis of the expected costs and benefits. NATURAL HISTORY AND MORPHOLOGIC FEATURES Overall, the 5-year survival rate for colorectal cancer is 52%. Localized disease is associated with a much better survival rate (84%) than is regional or distant disease (56% and 6%, Address reprint requests to Dr. R. L. MacCarty, Department of Diagnostic Radiology, Mayo Clinic, Rochester, MN 55905. Mayo Clin Proc 67:253-257, 1992
respectively).' Most experts believe that early detection of colorectal cancer substantially increases the patient's chance of survival. Removal of precancerous adenomatous polyps has been shown to decrease the incidence of carcinoma by 85%.2 There is evidence that colonic carcinomas generally evolve from preexisting benign lesions (that is, areas of epithelial dysplasia with or Without frank formation of an adenoma).' Most adenomatous polyps, however, do not become carcinomas; in the ones that do, usually many years elapse before this process occurs. The mean time for malignant transformation has been estimated to be 3.6 years for adenomas associated with severe dysplasia and 18 years for adenomas associated with mild dysplasia.t-' In two studies in which polyps were evaluated for a mean of 5 or more years, more than 50% showed no growth, slightly more than 33% grew, and 14% actually decreased or disappeared completely.6,7 The demonstrated stability of most polyps and the generally long lead time for malignant transformation are reasons for optimism in determining strategies to decrease the incidence of colonic carcinoma and the associated mortality through early detection of malignant and premalignant lesions. The morphologic features of a lesion in the colon are helpful in predicting the likelihood of malignant involvement. Pedunculated lesions are unlikely to harbor a malignant changer" however, if they do, they are much less likely to metastasize than is a sessile lesion of comparable size'? (Fig. I and 2). Histologically, adenomatous polyps are classified as 253
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
Mayo Clin Proc, March 1992,Vol 67
Fig. I. Barium enema examination, depicting l-cm pedunculated adenoma (arrow) in sigmoid colon.
Fig. 2. Barium enema examination, showing l-cm sessile carcinoma (arrow) in sigmoid colon.
tubular, tubulovillous, and villous. The higher the percentage of villous features, the more likely that foci of carcinoma will be encountered (Table I). The exception is the so-called carpet lesion, which does not seem to have the same high malignant potential as a more polypoid villous tumor" (Fig. 3). In general, the diameter of the lesion must be between 1 and 2 em to detect villous features grossly. Features that suggest villous elements within a lesion include innumerable small to tiny fingerlike lobulations and a granular surface pattern. A direct correlation exists between the size of a polypoid lesion and the likelihood of malignant disease. I I Size is the most important variable for assessing malignant potential (Table I). A related important factor is rate of growth, which is usually expressed in terms of doubling time (l doubling
time = 25% increase in diameter). In a recent study, the doubling time for adenomas was 5.83 years, and for carcinomas, it was 2.38 years." Therefore, rapid growth on serial examinations suggests a malignant process (Fig. 4 and 5). Furthermore, a previously demonstrated pedunculated polyp that grows in such a way as to obliterate its pedicle is likely to be a carcinoma.
254
Table I.-Likelihood of Malignant Foci Within Colorectal Adenomas on the Basis of Histologic Type and Size Malignant foci (%) Histologic type
2 cm
Tubular Tubulovillous Villous
1.0 3.9 9.5
10.2 7.4 10.3
34.7 45.8 52.5
Modified from Muto and associates. 11 By permission of J. B. Lippincott Company.
SCREENING FOR COLORECTAL POLYPS AND CANCER Because of the lengthy natural history of premalignant adenomas, colorectal cancer is well suited for screening. Analysis of stool specimens for occult blood has been widely heralded as a first-line screening test to identify a subgroup of patients who might benefit from radiologic or endoscopic assessment. In most cases, however, gastrointestinal blood loss is not due to a colorectal neoplasm. In addition, cancerous lesions tend to bleed intermittently; this factor causes false-negative results of fecal occult blood tests. Because most small adenomas do not bleed, they are unsuitable for screening by such tests." Therefore, even with widespread use of fecal occult blood tests, a large percentage of the population will still be at risk for colorectal adenomas and carcinomas. Whether selected by screening or by case finding, numerous patients are referred for complete colon examinations, and many more could potentially benefit.
Mayo Clio Proc, March 1992, Vol 67
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
255
Fig. 3. Barium enema examination, depicting large carpetlike villous adenoma occupying cecum. Barium fills multiple variegated spaces among innumerable frondlike projections that arise from surface of lesion. (From MacCarty RL: Radiology of the alimentary tract. In Clinical Medicine. Vol 10, Chapter 57. Edited by JA Spittell Jr. Philadelphia, Harper & Row, Publishers, 1986, pp 1-56. By permission of J. B. Lippincott Company.)
Many published articles that purport to show the superiority of colonoscopy in comparison with barium enema examination are flawed for one or more of the following reasons: (I) colonoscopy was used as the "gold standard," and no mechanism was included in the study design to uncover missed diagnoses; (2) high-quality endoscopy was compared with low-quality radiology; (3) usually, colonoscopies were performed after the barium enema examination, and the colonoscopist was not blinded to the results of such previous studies; (4) references to the radiologic literature included old reports (ones published before the availability of modem double contrast techniques). Both single contrast barium enema examination with careful fluoroscopically guided manual compression and stateof-the-art double contrast barium enema examination will detect 80 to 94% of colonic polyps'v'? and 90 to 98% of colonic carcinomas.":" At the Mayo Clinic, our experience is that colonoscopy and barium enema examination are approximately equally sensitive in detecting polypoid lesions of 7 to 10 mm or larger.
Fig. 4. Barium enema examination, disclosing tiny (approximately 2 mm in diameter) benign polyp (arrows) in transverse colon, demonstrated on three examinations during 4 years and showing no change in size. (Metallic 2-cm graduated scale is adjacent to polyp.)
256
Mayo elin Proc, March 1992, Vol 67
BARIUM ENEMA IN DIAGNOSING COLORECTAL CANCER
Fig. 5. A, Initial barium enema examination, revealing sessile polyp (arrow) (approximately 8 mm in diameter) in sigmoid colon. B, Nineteen months later, lesion had grown to a diameter of almost 2 cm. Carcinoma was proved at operation.
Because of the comparable or almost comparable sensitivity ofcolonoscopy and barium enema examination, the greater cost of colonoscopy (at least twice as much as barium enema), and the increased risk of complications (rate of perforation, I in 500 colonoscopies versus I in 5,000 to 10,000 barium enema examinations), the barium enema examination is preferred for the initial evaluation of the entire colon for colorectal neoplasms. A major limitation of colonoscopy is that the cecum cannot be visualized in 10 to 36% of cases. 2 1-24 Because approximately a fourth of the carcinomas occur in the cecum, colonoscopy will fail to detect 25% of cancerous lesions about 20% of the time, even if the sensitivity were 100% in the visualized portions of the colon. The demonstrated and acknowledged superiority of colonoscopy for detecting minute polyps does not justify its use as a screening procedure because the rate of perforation and associated mortality are greater than is the incidence of malignant polyps of 5 mm or smaller. Several studies have shown that barium enema examinations are not only less expensive and safer than colonoscopy but also more cost-effective, even when a higher sensitivity for colonoscopy has been assumed for cost-tobenefit calculations.P'"
MANAGEMENT OF PATIENTS WITH COLORECTALPOLVPS
never harbor malignant disease, and in a considerable percentage of cases, they are hyperplastic rather than adenomatous. When diminutive polyps are discovered during a barium enema examination, they may be safely monitored (Fig. 4); however, when they are found incidentally at endoscopy, they should be removed, if possible. The follow-up and management of patients who have had polyps removed are controversial, and definitive data that support a specific strategy are lacking. A suggested strategy based on the size, number, and histologic features of the index polyps is outlined in Figure 6 and assumes that patients are in either a high-risk or a low-risk category. 29 Both colonoscopy and barium enema examination have roles in such a strategy. The one (albeit substantial) advantage of colonoscopy over barium enema examination is the ability to remove polyps during the procedure. Thus, colonoscopy is a reasonable choice for surveying the colon when polyps have previously been diagnosed and are therefore likely to be encountered again, especially in patients who have had multiple polyps. After all polyps have been removed, however, the costeffectiveness of repeated colonoscopies at frequent intervals diminishes, and the risks become difficult to justify. Survey examinations ofthe colon may then be done by using barium enema at appropriate intervals. The need for clinical trials to test the success of this and other management strategies is obvious.
The ability to predict, by using barium enema examination, the biologic importance of a polypoid lesion on the basis of morphologic features and size has substantial implications in patient management. From a practical standpoint, a I-em or larger polyp, regardless of its morphologic aspects, is potentially cancerous and should be removed for histologic study, unless clinical factors (for example, terminal illness) dictate otherwise. Diminutive polyps (smaller than 5 mm) virtually
Endoscopy and barium enema examination are powerful techniques with complementary strengths and weaknesses. The current state of the science and art of medicine and the current and future medical-economic environment necessitate the judicious use of both procedures to decrease the incidence of colorectal cancer and the associated mortality.
CONCLUSION
BARIUM ENEMAIN DIAGNOSING COLORECTAL CANCER
Mayo Clin Proc, March 1992,Vol67
Solitary index polyp Pedunculated or sessile polyp with tubular histologic features
