Congenital Rhabdomyosarcoma Presenting as a Neck Mass at Birth
(a, b) H&E stain at medium magnification show both discrete nodules of spindle cells (a) as well as individual spindle cells infiltrating among variably atrophic skeletal muscle fibers and collagenized stroma (b). Mitoses were conspicuous, and there was no anaplasia or significant pleomorphism. (c, d) Immunohistochemistry stains demonstrate scattered nuclear positivity with myogenin (c) and strong cytoplasmic positivity with desmin in a majority of cells (d). The Ki-67 proliferative index was around 40%.