Abstract
ObjectivesTo assess whether electronic cleansing (EC) of tagged residue and different computed tomography (CT) windows influence the size of colorectal polyps in CT colonography (CTC).MethodsA database of 894 colonoscopy-validated CTC datasets of a low-prevalence cohort was retrospectively reviewed to identify patients with polyps ≥6 mm that were entirely submerged in tagged residue. Ten radiologists independently measured the largest diameter of each polyp, two-dimensionally, before and after EC in colon, bone, and soft-tissue-windows, in randomised order. Differences in size and polyp count before and after EC were calculated for size categories ≥6 mm and ≥10 mm. Statistical testing involved 95% confidence interval, intraclass correlation and mixed-model ANOVA.ResultsThirty-seven patients with 48 polyps were included. Mean polyp size before EC was 9.8 mm in colon, 9.9 mm in bone and 8.2 mm in soft-tissue windows. After EC, the mean polyp size decreased significantly to 9.4 mm in colon, 9.1 mm in bone and 7.1 mm in soft-tissue windows. Compared to unsubtracted colon windows, EC, performed in colon, bone and soft-tissue windows, led to a shift of 6 (12,5%), 10 (20.8%) and 25 (52.1%) polyps ≥6 mm into the next smaller size category, thus affecting patient risk stratification.ConclusionsEC and narrow CT windows significantly reduce the size of polyps submerged in tagged residue. Polyp measurements should be performed in unsubtracted colon windows.Key Points• EC significantly reduces the size of polyps submerged in tagged residue.• Abdominal CT-window settings significantly underestimate 2D sizes of submerged polyps.• Size reduction in EC is significantly greater in narrow than wide windows.• Underestimation of polyp size due to EC may lead to inadequate treatment.• Polyp measurements should be performed in unsubtracted images using a colon window.
Highlights
Computed tomography colonography (CTC) is the radiological examination of choice for the diagnosis of colorectal neoplasia [1].The evaluation of CTC examinations may be limited by residual stool and fluid, and either simulating or obscuring polypoid colonic lesions
The CTC image data within this database were acquired as a part of three Institutional Review Board (IRB)-approved prospective screening trials with the aim of assessing the performance of CTC compared to optical colonoscopy (OC) to screen patients at average risk for colorectal cancer [7,8,9]
There were 37 patients (11 women, 26 men; age 50-76; mean age 59.08) with a total of 48 polyps ≥6 mm (33 small polyps, 6-9mm; 15 large polyps, ≥10mm; 34 adenomas, 14 non-adenomas) that were completely submerged within tagged faecal residue in at least one of both scanning positions who were included in the study (ESM Table S1)
Summary
The evaluation of CTC examinations may be limited by residual stool and fluid, and either simulating or obscuring polypoid colonic lesions. Soft-tissue lesions submerged within hyperdense tagged faecal residue can be depicted on 2D images. Colonic mucosa that is obscured by tagged faecal residue is not accessible to endoluminal three-dimensional (3D) views and requires additional time-consuming two-dimensional (2D) evaluation. EC has been shown to improve colonic evaluation and polyp detection [4,5,6]. It has not been determined in vivo, as yet, whether EC affects the size of polyps that are submerged under tagged faecal residue. Related size differences may influence clinical reporting of polyps and, patient treatment
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