Imaging of periosteal reactions associated with focal lesions of bone.

Periosteal reaction (PR) is the response of cortical bone to an underlying insult. It is manifest in a limited number of histological and radiological patterns. Although not specific for a particular diagnosis, the appearance of PR aids the radiological characterization of bone lesions. Once ossified, PR is demonstrated well on plain radiography but can also be visualized on ultrasound, CT, MRI and bone scintigraphy, particularly in the early stage. This article provides a pictorial review of the patterns of PR with particular reference to bone tumours.