Strain and Shear-Wave Elastography and Their Relationship to Histopathological Features of Canine Mammary Nodular Lesions

SIMPLE SUMMARY: Canine mammary tumours are the most represented neoplastic disease in canine medicine with relevant implications for the health of dogs. Diagnostic imaging offers tools able to better define lesion characteristics to improve treatment strategies. In recent years, sonoelastography, derived from classical ultrasonography, was studied for its ability to quantify in a semi-quantitative or quantitative manner the stiffness of tissue. In this study, two different methods, one semi-quantitative, namely strain elastography, and one quantitative, namely shear-wave elastography, were compared for their ability to quantify the properties of naturally onset canine mammary tumours. Shear-wave elastography was found to be more replicable, and both techniques were correlated with the amount of connective tissue of the lesion, suggesting that this attribute is largely responsible for the stiffness of the mammary lesion. Both elastographic techniques, however, were not able to distinguish between benign and malignant mammary tumours, which had a wide variable content in the connective tissue. The findings suggest that sonoelastography is useful for characterizing connective tissue content in the canine mammary tumour but should be used in conjunction with other techniques to define the malignancy of the lesion. ABSTRACT: Mammary gland tumours have a significant impact on the health of dogs, requiring diagnostic tools to support clinicians to develop appropriate therapeutic strategies. Sonoelastography is an emerging technology that is able to define the stiffness of the tissue and has promising applications in the evaluation of mammary gland lesions. In the present study, strain elastography (STE) and shear-wave (SWE) elastography were compared in 38 mammary nodular lesions for their ability to define the histopathological features of canine mammary lesions. Among the techniques, SWE showed better repeatability (intraclass correlation coefficient: 0.876), whereas STE was found to be only acceptable (intraclass correlation coefficient: 0.456). Mammary nodular lesions showed a wide range of tissue stiffening with a similar mean value for STE and SWE in benign (4 ± 0.3 and 115.4 ± 12.6 kPa, respectively) and malignant lesions (3.8 ± 0.1 and 115.5 ± 4.5 kPa, respectively). A significant correlation was found between lesion fibrosis and STE (STE-I: r = 0.513, p < 0.001; STE-R: r = 0.591, p < 0.001) or SWE-S (r = 0.769; p < 0.001). In conclusion, SWE was reliable and correlated with fibrosis and was similar for both benign and malignant lesions, suggesting that other collateral diagnostic techniques should be considered in conjunction with SWE to characterize mammary nodular lesions in dogs.