An osteosarcoma usually arising from the metaphysis of long bones. It is characterized by the presence of a cystic architecture with blood-filled spaces. The prognosis is similar to that of conventional osteosarcoma. The disease is Monarch Disease Ontology entry MONDO_0004050 (telangiectatic osteogenic sarcoma). Also known as: malignant bone aneurysm, telangiectatic osteosarcoma, telangiectatic osteosarcoma (morphologic abnormality).