Figure 9d. Calvarial osteosarcoma after cerebral astrocytoma and surface femoral osteosarcoma. (a) Coronal T1-weighted MR image obtained in a 12-year-old girl shows a surface femoral osteosarcoma (arrow). The patient underwent surgery and chemotherapy. (b) Coronal contrast-enhanced T1-weighted MR image obtained 2 years later for seizures demonstrates a left hemispheric mass. The presumptive imaging diagnosis was a metastatic lesion, but surgical resection revealed anaplastic glioma. The patient underwent cranial irradiation. (c, d) Brain CT scans obtained 3 years later (d obtained at a lower level with bone windowing) reveal a calcified mass with new bone formation and a permeative pattern. (e, f) Axial T2-weighted (e) and coronal contrast-enhanced T1-weighted (f) MR images demonstrate the bone lesion with an accompanying soft-tissue mass. Histologic analysis demonstrated a highly atypical proliferation of mesenchymal cells with osteoid and trabecular bone differentiation.