Low grade malignant peripheral nerve sheath tumor with mesenchymal differentiation: a case report

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon neoplasm. Rarely, MPNST may display focal mesenchymal differentiation and this is more frequently encountered in high than low grade lesions. Here we present an example of a low grade MPNST with osteoid, cartilaginous and probably smooth muscle components occurring in the subtemporal fossa of a 26-year-old male patient with no associated neurofibromatosis type 1. The tumor exhibited diffuse S-100 protein expression, whereas immunostainings for epithelial membrane antigen and smooth muscle actin were positive in a portion of neoplastic cells.