From the case:
Spanish onion (photo)
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Spanish onion demonstrating alternating layers reminiscent of onion-skin periosteal reaction.
Photo credit: Dr Frank Gaillard
Case Discussion
Multilayered periosteal reaction, also known as a lamellated or onion skin periosteal reaction, demonstrates multiple concentric parallel layers of new bone adjacent to the cortex, reminiscent of the layers on an onion.