Colonoscopy Outperforms Barium Enema for Detection of Colorectal Cancer

ABSTRACT & COMMENTARY

The relative value of colonoscopy vs. barium enema (BE) for the detection of colorectal cancer has been debated for years. Recently, a group of gastroenterologists compared the performance of both techniques by reviewing the sensitivity of diagnostic procedures performed in the three years before the diagnosis of colorectal cancer in 2198 patients from 20 different hospitals. To determine the sensitivity of each method, each case was classified based on which procedure was performed for the initial evaluation of a sign or symptom; thus, cases were designated as primary BE or primary colonoscopy. If the BE detected the lesion, it was scored as a positive, whereas if the BE missed the lesion and a subsequent colonoscopy was positive, it was scored as a BE miss, not a colonoscopy success.

Of the 1660 patients diagnosed by either BE or colonoscopy, diagnosis was by primary BE in 719 and by primary colonoscopy in 941; 533 cases were detected by some other method. The indications for evaluation of patients were different for the two procedures, and this could have influenced the outcome of the study. Both procedures were used with equal frequency to evaluate anemia, but BE was performed more commonly for abdominal pain with or without weight loss and for altered bowel habits; colonoscopy was used more often for screening and to evaluate gross or occult bleeding.

BE missed 123 of 719 cancers in patients where it was the primary diagnostic procedure (sensitivity, 82.9%) and colonoscopy missed 47 of 941 cancers (sensitivity, 95%). The use of double-contrast BE did not significantly improve the sensitivity, 85.2% vs. 81.8%. A miss was 3.93 times more likely with BE than with colonoscopy. Colonoscopy was more sensitive than BE regardless of tumor location, although both tests were most sensitive for tumors in the descending colon and least sensitive for tumors in the cecum. Colonoscopy was significantly more effective at detecting early (Dukes A) lesions, but because the indications for colonoscopy included screening, this result may have been related to the indications for the examination rather than the superiority of colonoscopy. A multivariate analysis suggested that colonoscopy was a significant factor in detecting early lesions. When colonoscopy failed to detect cancer, it did so because of a failure to reach the lesion in 43% of the cases and passing the malignancy without seeing it in 57% of the cases. (Rex DK, et al. Gastroenterology 1997;112:17-23.)

COMMENTARY

The use of colonoscopy to detect colorectal cancer increased by 50% during the period from 1985-1992 and was accompanied by a complementary decrease in BE. Although many physicians have come to their own opinion regarding the relative value of these tests, a careful comparison of the two in large numbers of patients had not previously been performed. This article, which analyzed more than 1600 patients, indicates that colonoscopy is superior to BE for the detection of colorectal cancer in general clinical practice. These observations confirm our own impression and suggest that BE is best reserved for special circumstances.

This study was performed by gastroenterologists and, in the spirit of balance, the journal included an editorial by a radiologist, who not surprisingly raised a number of objections to the study and its conclusions. For example, patient selection could have biased the results (the old reliable criticism of any nonrandomized trial). The indications for employing the two methods were different. He also argued without data that older, sicker patients were referred for BE rather than colonoscopy. He blamed the poor BE sensitivity on poor bowel preparation, a problem that should have also affected colonoscopy. He quickly bypassed the issue of technical skill and moved on to the real issue—money. BE is cheaper than colonoscopy. The editorial appears to appeal (pander?) to third-party payers on the basis of economics rather than persuade other physicians based on efficacy. To wit: "If the barium enema finds mainly the keepers (and it does) at one-third the cost, it deserves full and complete recognition by neutral third parties." I must be missing something because the third parties I know about are anything but neutral when it comes to costs. The battle to save BE does not appear to be winnable on the basis of the data.

We are swayed by the data in this study, which reinforce our own approach to patients suspected of having colon cancer. Colonoscopy is more sensitive than BE and, even more importantly, provides the opportunity to detect and remove precancerous polyps. BE has a sensitivity of only 44% for polyps greater than 1 cm, and, if such polyps are detected, a colonoscopy is required to deal with them. Thus, in addition to the enhanced sensitivity of detection and the advantage in early diagnosis, colonoscopy provides the opportunity to interrupt the natural history of polyps converting to carcinoma.

Other interesting observations in this paper include the authors’ inability to identify a significant improvement in early detection through the use of the double-contrast BE. No part of the colon was visualized better with BE. Experience had an impact on the colonoscopy results but did not appear to influence BE results. The location of the diagnostic facility (university vs community hospital) did not influence the results nor did the level of specialization of the radiologist (i.e. gastrointestinal radiologist vs general radiologist). However, the training of the endoscopist had a significant impact on the outcome of colonoscopy. Board-certified gastroenterologists were superior to any other physicians operating the colonoscope. We hope that third party payers and HMOs realize the importance of the various attributes of colonoscopy over BE and permit colonoscopy as the diagnostic maneuver of first choice in a patient with symptoms that could be colorectal cancer.