Points to remember:

Mainly located near the metaphysis/diaphysis of long bones. Less often in flat bones or vertebral bodies.
Usually osteolytic lesions (motheaten, or permeative) with a soft-tissue component.
Periosteal reactions if seen can be:
– Spiculation (periosteal new bone formation radiating into the soft tissues)
– Onionskin periosteal reaction.
– Codman’s triangle: elevated ossified periosteum at the margin of the subperiosteal tumour.
– “Sunburst” appearance

On imaging, the main differential diagnosis is osteosarcoma without a matrix.