## Classification of Giant Cell Tumor by Location **Key Point:** Giant cell tumor (GCT) of bone characteristically arises in the **epiphysis and extends into the metaphysis** after skeletal maturity, typically in the distal femur, proximal tibia, and distal radius. ### Anatomical Pattern - **Epiphyseal origin:** Arises in the epiphysis (distal to the growth plate) - **Metaphyseal extension:** Extends into the metaphysis as the tumor grows - **Timing:** Occurs after physeal closure (skeletal maturity), typically in patients aged 20–40 years - **Eccentric location:** Usually eccentric within the epiphysis, reaching the articular surface ### Common Sites (in order of frequency) | Site | Frequency | Typical Location | | --- | --- | --- | | Distal femur | 20% | Epiphyseal, extends metaphyseal | | Proximal tibia | 16% | Epiphyseal, extends metaphyseal | | Distal radius | 12% | Epiphyseal, extends metaphyseal | | Proximal humerus | 5% | Epiphyseal | | Distal tibia | 5% | Epiphyseal | **High-Yield:** The **epiphyseal location with metaphyseal extension** is a hallmark imaging feature that helps differentiate GCT from other bone tumors (e.g., osteosarcoma is metaphyseal; chondroblastoma is purely epiphyseal). **Clinical Pearl:** In skeletally immature patients, a similar lesion arising in the epiphysis without metaphyseal extension is more likely chondroblastoma, not GCT. 
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