• 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