RESUMO
Among the diverse causes of posterior mediastinal masses, malignant peripheral nerve sheath tumors is a very rare neurogenic tumor. Imaging features tend to be variable. A 20-month-old toddler presented with a 3-month history of persistent diffuse thoracic and abdominal pain. A chest magnetic resonance imaging was taken and shown a posterior mediastinal lesion. Histopathology and immunohistochemical analysis confirmed the diagnosis of a malignant peripheral nerve sheath tumor with myxoid areas. Malignant peripheral nerve sheath tumors are an uncommon entity in the children with a poor prognosis. Magnetic resonance imaging is the preferred technique in children to limit the use of ionizing radiation and because has a higher contrast resolution; however, all suspicious tumors should be biopsied to make an appropriate diagnosis. Treatment is radical surgery with excision of the entire mass; however, there is a high incidence of local recurrence.