Although colorectal cancer has majo...

Although colorectal cancer has major public health implications, many patients who are eligible for routine screening resist colonoscopy because the measure is invasive and carries a risk of perforation. Virtual or comput tomographic colonoscopy (CTC) may give an advantage over standard colonoscopy in these reveres but it is not known in what way well it performs in routine practice. Available studies report a wide range in sensitivity for detecting lesions 10 mm or larger in size. Generally, the ability to discover lesions greater than 6 mm is desirable. Cotton and associates manner of lifeed this multicenter study to compare the performance of CTC with that of standard colonoscopy in routine practice settings.

Participants 50 years and older with an indication for colonoscopy underwent cathartic preparation of the colon before CTC followed by the agency of regular colonoscopy. Dur-ing the latter, eventuates from the CTC were revealed segmentally to help the colonoscopist identify any discrepancies in the sum of two units examinations. This combination of screening experiment segmental unblinding, and information from any further diagnostic testing was considered the criterion standard, with essentially 100 percent positive predictive value. The issue measures were the sensitivity and specificity of CTC and colonoscopy with regard to lesions 6 mm or larger.

A total of 600 patients had the pair procedures, with 827 lesions descryed Of these, 79.1 percent were 1 to 5 mm in size, 144 percent were 6 to 9 mm and 65 percent were at least 10 mm Of the 173 lesions larger than 6 mm 29 were advanced lesions set up in 104 participants. CTC identified 41 participants with lesions 6 mm or larger, whereas colonscopy identified 103 participants. Of the 496 participants with smaller lesions, CTC identified 449 patients, while colonoscopy identified all of them. Other measurements consistently showed better detection with conventional colonoscopy. Positive predictive values for detecting lesions of at least 6 mm and at least 10 mm with CTC were 466 percent and 500 percent respectively, compared with 100 percent for colonoscopy as part of the criterion standard. Negative predictive values for CTC were 877 percent compared with 998 percent with colonoscopy.

CTC had a reasonable sensitivity for detecting lesions, whether they were 6 mm or 10 mm No improvement in the accuracy of CTC or "learning curve" was evident as the studious mood progressed. Patients did not reveal a estimation for one procedure over the other, possibly because the two require bowel preparation beforehand. At this time, there is no evidence that CTC is useful in routine practice. With further technologic advancements and improvement in orderly dispositions of three-dimensional reconstructions, CTC may have broader application in the future

Cotton PB et al. Comput tomographic colonography (virtual colonoscopy). A multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA April 14 2004;291:1713-9

EDITOR'S NOTE: This article is a reminder of the limitations of colon cancer screening. (1) Clearly, virtual colonoscopy doesn't perform as well as the conventional way but when we are evaluating existing screening orders accuracy, acceptability, and cost also ne to be considered. Although colonoscopy is the criterion standard, its accuracy is unclear. Colonoscopy appears to ascertain only 90 percent of large lesions and 75 percent of lesions les than 1 cm (2) equable though a colonoscopic examination will miss a proportion of malignancies, in denominations of detecting lesions, it is still the best available screening tool to date. However, because the richnesss of even conventional colonoscopic screening are prohibitively high, a more cost-effective screening option, notably annual fecal mysterious blood testing and flexible sigmoidoscopy each five years, is probably preferable. (3) If advanced technology as it is as virtual colonoscopy brings improvement not simply in acceptability and accuracy, it will increase demand, which, in divert will require a rational plan for footing the bill.--C.W.

REFERENCES

(1) Walsh JM Terdiman JP Colorectal cancer screening. JAMA 2003;289:1288-96

(2) Imperiale TF Wagner DR Lin CY Larkin GN Rogge JD Ransohoff DF Risk of advanced proximal neoplasms in asymptomatic adults according to the distal colorectal findings. N Engl J M 2000;343:169-74

(3) Frazier AL, Colditz GA, Fuch C Kuntz KM Cost-effectiveness of screening for colorectal cancer in the general population. JAMA 2000;284:1954-61

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