Assessing Polyp Size by Improved Digitalized Computed Tomography (CT)

Abstract

Background: The size of colorectal polyps is important in the clinical management of these lesions. When using a conventional ruler (the tool of pathologists worldwide), we have previously found unacceptably high intra- and inter-observer variations in assessing the size of phantom polyps. The aim of this study was to assess the size of 12 phantom polyps by computed tomography (CT). Materials and Methods: The size of phantom polyps as assessed by CT was compared to the gold standard size (GSS) measured at The Royal Institute of Technology, Stockholm, Sweden. Results: In 33.3% (n=4) of the 12 polyps and in 41.7% (n=25) of the 60 measurements, the mean CT size under- or overestimated the GSS by more than 1 mm. In 15% , or in 9 of the 60 measurements, the CT size was under- or overestimated by more than 2 mm. In polyp #5 the GSS size was 8.41 mm where the expected cancer-risk in adenomas is 1% . But 3 out of 5 CT measurements were >10 mm, where the expected cancer-risk in adenomas is 10% . In polyp #10 the GSS size was 10.20 mm where the expected cancer-risk is 10% . But 2 out of 5 CT measurements were <10 mm where the expected risk is only 1% . Conclusion: The size assessed by CT was more reliable than that obtained with a millimetre ruler using the same devices, inasmuch as the disparate individual deviation-values found with the latter method were avoided. The volume and the shape of the devices influenced size assessment of phantom polyps by CT.