CliniealRadiology (1983) 34, 423-425 © 1983 Royal College of Radiologists
0009-9260/83/01100423502.00
Diagnosis of Carcinoma of the Colon by Barium Enema IAN BEGGS* and B. M. THOMAS
X-ray Department, St Mark 's Hospital, City Road, London Double-contrast barium enemas can detect 96% of colonic carcinomas. This is similar to the detection rate for colonoscopy. Single-contrast enemas compare badly. Small sigmoid tumours are most likely to be missed. Inadequate bowel preparation, single-contrast examinations and observer error account for most barium enema failures.
Accurate detection of carcinoma of the colon is essential because it is a common tumour (causing 10 000 deaths annually in England and Wales) and excision is potentially curative (Morson and Dawson, 1979). Hunt (1978) reviewed the literature and reported that barium enemas fail to diagnose 1 0 - 1 8 % o f colonic carcinomas. This does not agree with our experience or that of Miller (1977). It is particularly surprising, since most carcinomas of the colon develop from preexisting polyps (Morson, 1974) and double-contrast barium enemas can detect the vast majority o f polyps larger than 1 cm (Williams et al., 1974). PATIENTS AND METHODS We have r~iewed all histologically proven cases of carcinoma of the colon seen at St Mark's Hospital during the period 1976-1980. Carcinomas of the rectum were not included. There were 184 carcinomas of the colon. Twentyfour were excluded from further consideration. Seven patients presented with intestinal obstruction and the diagnosis was established at laparotomy in six and at autopsy in one. The diagnosis was made on clinical examination in five patients and discovered incidentally at laparotomy in one. The remaining 11 cases were inadequately documented but most were referred to St Mark's with the diagnosis already established.
RESULTS One hundred and sixty patients were available for analysis and these were divided into three groups (Table 1). 1. Barium Enema at St Mark's Ninety patients had a barium enema at St Mark's Hospital. Twenty-two also had colonoscopy. Barium enema missed three carcinomas: an annular sigmoid *Present address: X-Ray Department, Guy's Hospital, St Thomas Street, London.
Table 1 - Carcinomas missed at barium enema and colonoscopy
Enema at St Mark's Enema elsewhere Colonoscopy
Number of patients
Number of carcinomas missed
90 61 66"~
3 (3.3%) 10 (16.4%) 3 (4.5%)
~ Nine patients had colonoscopy only. tumour, a malignant 1 cm sigmoid polyp and a polypoid caecal tumour. Colonoscopy identified both sigmoid tumours but not the caecal carcinoma. This was diagnosed by repeat barium enema a year later and identified in retrospect on the original enema. Both sigmoid tumours were in segments of diverticular disease; there was considerable bowel spasticity adjacent to the sigmoid polyp. 2. Barium Enema at Other Hospitals Sixty-one patients had a barium enema, usually single-contrast, at another hospital. Thirty-five also had colonoscopy at St Mark's. Ten carcinomas were missed by barium enema; all were correctly identified by colonoscopy. Eight carcinomas were in the sigmoid colon, one was annular and seven were malignant polyps. Five of these polyps measured less than 2.5 cm in diameter. A polypoid carcinoma of the ascending colon was erroneously interpreted as the ileo-caecal valve by the reporting radiologist. A polypoid carcinoma of the caecum was not demonstrated because the patient was unable to retain the barium enema. A total of 14 barium enemas were performed on the 10 patients. One was a good-quality double-contrast barium enema but a sigmoid polyp was obscured by overlapping loops o f sigmoid colon. Three other double-contrast enemas were attempted (in two patients) but there was incomplete bowel distension and considerable faecal residue. The remaining 10
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CLINICAL RADIOLOGY
barium enemas (in seven patients) were single-contrast and in most of these there was inadequate bowel preparation. There were no colonoscopic failures in this group. 3. Colonoscopy at St Mark's Sixty-six patients had colonoscopy at St Mark's. Nine did not have a barium enema. Twenty-two had a barium enema at St Mark's and 35 were referred for colonoscopy after a barium enema at another hospital. Colonoscopy failed to identify three carcinomas. An annular carcinoma of the ascending colon could not be reached. An hepatic flexure polyp was not found at initial colonoscopy but was seen and successfully snared 6 months later and shown to be malignant. Both of these tumours were demonstrated by a barium enema performed at St Mark's. A caecal tumour was missed by colonoscopy and initial barium enema as previously described. The distribution of the missed carcinomas is shown in Fig. 1. Six were sigmoid polyps smaller than 2.5 cm.
Fig. 1 - Distribution of carcinomas missed by: D barium enema at St Mark's, • barium enema at other hospital, o eolonoscopy at St Mark's.
DISCUSSION
Carcinoma of the colon may present radiologically either as an overt tumour or as a polyp which is found to be malignant. The risk of malignancy in a polyp is about 1% for polyps smaller than 1 cm, about t0% for those between 1 cm and 2 cm and
almost 50% for those over 2 cm (Morson, 1974). Thoeni and Menuck (1977) identified 88.3% of all colonic polyps using double-contrast barium enemas but only 54.8% with single-contrast studies. Williams et al. (1974) showed that double-contrast enemas can detect 98% of polyps larger than 1 cm compared with 77% by single-contrast examinations although, in a more recent prospective study, even the doublecontrast enema was significantly less accurate than colonoscopy in the sigmoid colon and caecum (Williams et al., 1982). In our series, 13 carcinomas out of 160 were missed by barium enema. The three carcinomas missed at St Mark's were not identified by the reporting radiologist but were visible in retrospect. Two were in the sigmoid colon where there was coexistent diverticular disease and, in the case of a 1 cm polyp, severe bowel spasticity. All the St Mark's enemas were double-contrast studies (Thomas, 1980) except for six cases where there was complete obstruction to the flow of barium. In almost all, including the missed cases, bowel preparation was adequate. On the other hand, the 'outside' barium enemas missed 10 carcinomas. Only one of these examinations was an adequate double-contrast study and in this case a small sigmoid polyp was obscured by overlapping loops of bowel. Three attempted doublecontrast enemas were inadequate because of poor bowel preparation and incomplete bowel distension. The remaining 10 enemas were single-contrast studies and, in most of them, bowel cleansing was incomplete. One large tumour was incorrectly identified as the ileo-caecal valve. The overall barium enema failure rate was 8.6%. This is comparable with the 10% false negative rate for enemas recorded by Swarbrick et al. (1978). About 80% of their patients were referred to St Mark's from other hospitals for colonoscopy. Only 40% of our patients were referred for colonoscopy following an enema elsewhere but they accounted for 77% of the carcinomas missed at barium enema. We believe that the 10-18% barium enema 'miss rate' recorded by Hunt (1978) is due to the large proportion of patients who had inadequate barium examinations but who were considered to be sufficiently highrisk patients to require colonoscopy. We agree with Miller (1977) that these patients require a high-quality double-contrast barium enema. In our series, 10 of the missed tumours were in the sigmoid and six were less than 2.5 cm in diameter. This preponderance of carcinomas missed at barium enema in the sigmoid is not surprising. It is the commonest site for polyps and carcinomas and can be a difficult area to examine because of its tortuosity,
DIAGNOSIS OF CARCINOMA OF THE COLON BY BARIUM ENEMA
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overlapping loops, diverticular disease and small- first-choice investigation for suspected colonic neobowel barium reflux. However, it is easily and plasm supplemented b y sigmoidoscopy, especially accurately examined by flexible sigmoidoscopy with the flexible instrument and, where necessary, (Leicester et al., 1982). colonoscopy. The barium enema false negatives can, therefore, be attributed to the site (sigmoid), size (less than 2.5 cm), observer error (failure to identify or inter- REFERENCES pret correctly) and technique (single-contrast, poor de Lacey, G., Benson, M., Wilkins, R., Spencer, J. & Cramer, bowel preparation). Small sigmoid tumours are most B. (1982). Routine colonic lavage is unnecessary for double-contrast barium enema in out-patients. British likely to be missed but can usually be detected by Medical Journal, 284, 1021-1022. flexible sigmoidoscopy (Leicester et al., 1982). Gelfand, D. W., Wu, W. C. & Ott, D. J. (1979). The extent of Observer error accounted for at least four cases. All successful colonoscopy: its implications for the radiologist. three tumours missed on barium enema at St Mark's Gastrointestinal Radiology, 4, 75 -78. Hughes, K., Mann, S., Cooke, M. B. D. & James, W. B. (1983). were correctly identified in retrospect by a second A new oral bowel evacuant (Picolax) for colon cleansing. observer, as was a polypoidal caecal carcinoma inClinical Radiology, 34, 75-77. correctly interpreted as the ileo-caecal valve at another Hunt, R. H. (1978). Rectal bleeding. Clinics in Gastrohospital. This highlights the need for more careful enterology, 7, 719-740. viewing of double-contrast barium enemas as advo- Kelvin, F. M., Gardiner, R., Vas, W. & Stevenson, G. W. (1981). Colorectal carcinoma missed on double-contrast cated by Kelvin et al. (1981). Correct technique is barium enema study. American JournalofRoentgenology, essential. Miller (1977) has previously recorded the 137, 307-313. greater accuracy of double-contrast barium enemas Leicester, R. J., Pollett, W. G., Hawley, P. R. & Nicholls, than of single-contrast enemas in detecting colonic R. J. (1982). Flexible fibreoptic sigmoidoscopy as an outpatient procedure. Lancet, i, 34-35. tumours. Our figures confirm this. Adequate bowel Miller, R. E. (1977). The barium enema in the high-risk preparation is vital for b o t h barium enema and carcinoma patient. Radiology, 123, 813-815. colonoscopy, yet it appears to be a particular problem Morson, B. (1974). The polyp cancer sequence in the large for some X-ray departments. We still prefer to bowel. Proceedings of the Royal Society o f Medicine, 67, prepare patients by low-residue diet, aperient and 451-457. colonic washout but some workers claim that lavage Morson, B. C. & Dawson, I. M. P. (1979). Gastro-intestinal Pathology, pp. 615-680. Blackwell Scientific, Oxford. is unnecessary (de Lacey et al., 1982; Hughes et al., Swarbrick, E. T., Fevre, D. I., Hunt, R. H., Thomas, B. M. & 1983). Williams, C. B. (1978). Colonoscopy for unexplained The failure rate for enemas at St Mark's (3.3%) is rectal bleeding. British Medical Journal, 2, 1685-1687. similar to its colonoscopic failure rate (4.5%) and to Thoeni, R. F. & Menuck, L. (1977). Comparison of barium enema and colonoscopy in the detection of small colonic the involuntary incomplete colonoscopy rate recorded polyps. Radiology, 124, 631-635. by Swarbrick et al. (1978), Williams and Teague Thomas, B. M. (1980). Barium enema: the Malmo technique. (1973) and Waye (1977), although lower than that In Abdominal Operations, 7th edn, ed. Maingot, R., pp. reported by Gelfand et al. (1979). A specific advantage 2089-2095. Appleton Century Crofts, New York. of colonoscopy is that it provides a tissue diagnosis. Waye, J. D. (1977). Colitis, cancer and colonoscopy. Medical Clinics of North America, 62, 211-224. Thirty-seven patients in our series had a colonoscopic Williams, C. B., Hunt, R. H., Loose, H., Riddell, R. H., Sakai, polypectomy. This provided a histological diagnosis Y. & Swarbrick, E. T. (1974). Colonoscopy in the and, where the pathologist confirmed that excision management of colon polyps. British Journal of Surgery, was complete, sufficient treatment. 61, 673-682. We conclude that the double-contrast barium Williams, C. B., Macrae, F. A. & Bartram, C. I. (1982). A prospective study of diagnostic methods in adenoma followenema is more accurate than the single-contrast up. Endoscopy, 14, 74-78. enema and comparable with colonoscopy in the Williams, C. B. & Teague, R. H. (1973). Progress report: detection o f colonic carcinoma. It should remain the colonoscopy. Gut, 14,990-1003.
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