Locoregional staging using magnetic resonance imaging in rectal cancer: influence of diffusion-weighted imaging in the diagnostic accuracy

Abstract

Objective: To assess whether the accuracy in locoregional staging using magnetic resonance imaging (MRI) in rectal cancer (primary or post-chemoradiotherapy) improves by adding diffusion-weighted imaging, according to the radiologist’s degree of experience. Method: Retrospective study on 100 MRI records (1.5 T, 2011-2016) from patients with rectal cancer (reference standard: histology of surgical specimens). Ten radiologists (three experienced in rectal cancer, three specialized in other areas and four residents) individually reviewed each case twice: first, evaluating just high-resolution T2-weighted sequences; second, evaluation of diffusion-weighted plus high-resolution ones. The analysis focused on the differentiation between early (0-I) and advanced (II-IV) stages. Accuracy, sensitivity/specificity and predictive values were calculated. Results: Experienced radiologists showed some worsening by adding diffusion-weighted imaging, mainly at primary staging (accuracy: 0.769 to 0.701). Inexperienced radiologists presented a post-chemoradiotherapy improvement (accuracy: 0.574 to 0.642; specificity of 19.1 to 29.8%), although with no other remarkable changes. Residents demonstrated a worsening at primary staging by adding diffusion (accuracy: 0.670 to 0.633; specificity: 45.8 to 39.6%), but post-chemoradiotherapy improvement (sensitivity: 80.6 to 87%). The differences between both reviews were not statistically significant. Conclusions: No significant differences were found in the distinction between early and advanced rectal tumors secondary to adding diffusion-weighted imaging to high-resolution T2-weighted sequences.