Computed tomographic colonography, also called virtual colonoscopy, is an evolving technology under evaluation as a new method of screening for colorectal cancer.
However, its performance as a test has varied widely across studies, and the reasons for these discrepancies are poorly defined.
Dr Mulhall and colleagues systematically reviewed the test performance of computed tomography colonography compared to colonoscopy or surgery and to assess variables that may affect test performance.
The researchers searched PubMed, MEDLINE, and EMBASE databases and the Cochrane Controlled Trials Register for English-language articles published between 1975 and 2005.
The team included prospective studies of adults undergoing computed tomographic colonography after full bowel preparation, with colonoscopy or surgery as the gold standard.
The research team selected studies that had used state-of-the-art technology, including at least a single-detector computed tomographic scanner with supine and prone positioning.
The included studies also had to have insufflation of the colon with air or carbon dioxide, collimation smaller than 5 mm, and both 2-dimensional and 3-dimensional views during scan interpretation.
The evaluators of the colonogram had to be unaware of the findings from use of the gold standard test.
|The sensitivity was heterogeneous but improved as polyp size increased for detection of polyps less than 6 mm|
|Annals of Internal Medicine|
The team absracted data on sensitivity and specificity overall and for detection of polyps less than 6 mm, 6 to 9 mm, and greater than 9 mm in size.
Sensitivities and specificities weighted by sample size were calculated, and heterogeneity was explored by using stratified analyses and meta-regression.
The investigators found that 33 studies provided data on 6393 patients.
The sensitivity of computed tomographic colonography was heterogeneous but improved as polyp size increased by 48 % for detection of polyps less than 6 mm, 70% for polyps 6 to 9 mm, and 85% for polyps more than 9 mm.
The team noted that the characteristics of the computed tomographic colonography scanner, including width of collimation, type of detector, and mode of imaging, explained some of this heterogeneity.
In contrast, specificity was homogenous with 92% for detection of polyps less than 6 mm, 93 % for polyps 6 to 9 mm, and 97 % for polyps more than 9 mm.
The researchers observed that the studies differed widely, and the extractable variables explained only a small amount of the heterogeneity.
In addition, the researchers reported that only a few studies examined the newest computed tomographic colonography technology.
Dr Mulhall's team concluded, "Computed tomographic colonography is highly specific, but the range of reported sensitivities is wide."
"Patient or scanner characteristics do not fully account for this variability, but collimation, type of scanner, and mode of imaging explain some of the discrepancy."
"This heterogeneity raises concerns about consistency of performance and about technical variability."
"These issues must be resolved before computed tomographic colonography can be advocated for generalized screening for colorectal cancer."