<prompt> Expansile lytic lesion at skull base typically involving clivus with specks of calcification is suggestive of NOT RELATED-RADIOOsteosarcomaSecondaries in boneSecondaries in boneFibrous histiocytoma  <response>: It is a destructive bone tumour believed to arise from ectopic remnants of notochord notochord cell rest.Its maximum incidence between 50-70 years.It is locally malignant with strong tendency to recur after excision.Predilection for sacral 50 and cranial 40 regions the extreme ends of the axial skeleton; In sacrum at s4 and s5 and in cranium basisphenoid clivus and dorsal aspect of sellaAbove sacrum and below c2, chordomas are rare.Radiologically appears as a oval or lobulated well-defined purely lytic mass in midline, which may contain calcification and a soft tissue component.Recurrence rate is high but it metastasis occurs late.Chordoma at the base of skull carry best prognosis 