SWE of Low risk benign breast lesions, which pathologic diagnoses makes them stiff

Purpose: To compare stiffness of high-risk(HR) and low-risk benign breast lesions (LR) and to evaluate range of pathologic basis of LR that appear stiff in SWE. Methods and Materials: Retrospective analysis of SWE of 381pathologically confirmed benign lesion(18 HR/363LR) was done. SWE images were correlated with pathological results. Qualitatively elasticity was displayed with colour-coded map ranging from 0kPa(dark blue;soft) to 180kPa(red;stiff). Quantitative elasticity values were measured over the stiffest portion. Maximum &mean stiffness, &ratio to surrounding tissue were compared between HR and LR using Mann-Whitney Utest. Results: Meanstiff and maximum stiffness and ratio to normal tissue were 42.08 ,52.06, 3.11 and 23.64, 33.26, 2.09 in the HR& LR categories (significant at p=0.02). HR included papillary lesions,atypical ductal hyperplasia, atypical adenosis, sclerosing adenosis, atypical ductal papillomatosis, LR included FCC, fibroadenoma, benign fibroepithelial lesion, usual hyperplasia without atypia, mastitis, granulomatous mastitis, stromal fibrosis, sclerosing adenosis, adipose tissue, cystic change, apocrine metaplasia, intraductal papilomatosis , fat necrosis, abscess formation, benign phylloides tumor, lymphocystic mastitis. There were 23 lesions in the LRgroup with mean stiffness above two SD above mean of 23.64(above 50 kpa). Pathologies in this group included benign fibroepithelial lesion or fibroadenoma (14),fibrocystic change(3), chronic mastitis(4), acute mastitis(1), sclerosing adenosis(2), Intraductal papilomatosis(1), stromal fibrosis(3),usual hyperplasia(1), fat necrosis(2). Conclusion: Many benign low-risk lesions can appear stiff in SWE. In these lesions SWE appearance can be misleading and lead to inadverent upgrading of the lesions in ultrasound.