What causes onion-skin periosteal reaction in bone on radiographic imaging?
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Onion-skin periosteal reaction occurs when new bone forms in multiple concentric layers around the cortex of a bone, typically seen on X-rays. This radiological sign is most commonly associated with aggressive lesions such as Ewing sarcoma but can also be seen in conditions like acute osteomyelitis, Langerhans cell histiocytosis, and some osteosarcomas. It indicates a pathological process where the periosteum is repeatedly stimulated to form new bone layers due to the underlying disease, often reflecting a cycle of rapid and intermittent insult or irritation to the bone.
Why is it called so?
It is called “onion-skin periosteal reaction” because the multiple, concentric layers of newly formed bone resemble the layered appearance seen when an onion is cut in cross-section. The term emphasizes the laminated, parallel layering pattern of the periosteal new bone formation.
Pathophysiology
The periosteum, a bone’s outer membrane, responds to repeated or cyclical irritation by laying down successive sheets of new bone. When a lesion such as a tumor or infection grows in fits and starts, the periosteum has intermittent time to deposit thin layers of new bone before being elevated again by the lesion’s expansion. This cyclical process leads to multiple concentric layers of bone on imaging, seen as the onion-skin periosteal reaction.
Alternative names: Lamellated periosteal reaction, Laminated periosteal reaction
Other associated named signs: Codman triangle, Sunburst pattern related to aggressive bone lesions
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