• Has the worst prognosis of the surface osteosarcomas
• Rare, very anaplastic tumor
• May be fibroblastic or osteoblastic
• Age and skeletal distributions similar to that of low-grade parosteal osteosarcomas
• Usually a destructive lesion on surface of the bone
• Controversial whether invasion of medullary canal is more frequent in high-grade parosteal osteosarcoma
• May have periosteal new bone formation with a spiculated pattern
• Soft tissue mass may be present
• Treatment similar to that of central osteosarcoma