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Deformation of breast masses between supine ultrasound and prone magnetic resonance imaging

Background Breast masses will deform between different postures and modalities in the background mammary gland. However, this difference in deformation between benign and malignant masses has not been studied. Purpose To investigate the feasibility of using the change of the longitudinal-transverse ratio (L/T) of a breast mass from supine ultrasonography (US) and prone magnetic resonance imaging (MRI) as representing deformation in differentiating between benign and malignant masses. Material and Methods The participants were 197 consecutive patients with 201 breast masses (55 benign, 146 malignant) who had undergone both US and MR examinations with histological diagnoses at our hospital from January 2012 to December 2014. On US, the largest transverse diameter of the mass (TUS) parallel to the pectoral muscle and the longitudinal diameter (LUS) perpendicular to the muscle were measured. On prone MRI, the largest transverse diameter of the mass (TMR) parallel to the pectoral muscle and the orthogonally oriented diameter as the longitudinal direction (LMR) were measured. The change of the L/T between these modalities was compared between benign and malignant masses. Results Malignant breast masses showed significantly smaller change of the L/T (median [interquartile range (IQR)] = 13.5% [4.29–24.4]) than benign ones (36.7% [24.3–52.4]) (P < 0.001). The optimum cut-off value of the change of the L/T for differentiating malignant from benign was 19.1%, with sensitivity, specificity, and area under the curve of 63.7%, 90.9%, and 0.834, respectively. Conclusion The change of the L/T may be a feasible and useful quantitative index for differentiating breast masses.