Aneurysmal bone cyst involving the distal half of the left second metatarsal. The etiology of this ABC was felt by the AFIP to be that of a subperiosteal giant cell tumor. In any event, this is a typical blow-out lesion of the bones of the foot or hand, characterized by marked expansion of the periosteal shell and, in this case, extension of an original metaphyseal lesion into the diaphysis and into the epiphysis down to the enlarged, flattened, articular surface.

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