Arises from surface of cortex beneath periosteum – does not infiltrate surrounding tissue, but mass extends into surrounding tissue; can occur at any age (end decade moat common); M=F;
Proximal humerus and femur are most common sites. Usually have mild pain at site – often palpate hard mass attached to bone.
X-ray – radiolucent oval soft tissue mass on periphery of cortex – usually have a thin distinct cortical reaction with some erosion of adjacent cortex.
Treatment – excision.