Concentric Expansion

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"Expansion" refers to bulging of the cortex. Symmetrical bulging of cortices is referred to as "Concentric Expansion" as in Bone Cyst, and asymmetrical- bulging is referred to as "Eccentric Expansion" as in Osteochondroma. Please note that all extraosseous lesion are to be considered "Eccentric Expansile."  For multiple lesions of the same kind you may select one lesion which demonstrates all the positive features, or you may combine the positive features from several lesions if no single lesion demonstrates all the features. For the bone location in multiple lesions,  choose the part of the bone which is predominantly involved e.g. diaphysis.   Similarly for skeletal location choose one bone which is predominantly involved.

                                                               Eccentric Expansion