Assessing polyp size by improved digitalized computed tomography (CT)

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).

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.

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%.

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.