Significant thickening of the sternocleidomastoid muscles (blue arrows). Soft tissue density obliterating numerous fat planes extending into the mediastinum and completely encasing the major vessels and left paraspinal musculature including the left trapezius muscle (red arrow). The very few cases of breast cancer metastatic to the soft tissues predominantly describe focal or mass-like involvement. This diffuse, infiltrating appearance is highly unusual and most characteristic of severe infection/inflammation such as myositis or necrotizing fasciitis.