## Most Common Primary Malignant Bone Tumor in Children **Key Point:** Osteosarcoma is the most common primary malignant bone tumor in children and adolescents, accounting for approximately 40% of all primary malignant bone neoplasms in this age group. ### Epidemiology & Location - **Peak incidence:** 10–25 years (coincides with growth spurts) - **Most common sites:** Distal femur (40%), proximal tibia (15–20%), proximal humerus (10%) - **Metaphyseal predilection:** Occurs at the metaphysis of long bones, particularly around the knee joint ### Imaging Characteristics | Feature | Osteosarcoma | |---------|---------------| | **Pattern** | Mixed lytic and sclerotic (mixed lucency) | | **Periosteal reaction** | Sunburst (radiating spicules), Codman triangle | | **Cortical involvement** | Cortical breakthrough common | | **Soft tissue mass** | Prominent extraosseous component | | **Margins** | Ill-defined, aggressive | ### Pathophysiology - Malignant tumor of osteoblasts producing osteoid and bone - Arises in metaphyseal regions of rapidly growing long bones - Associated with Li-Fraumeni syndrome (TP53 mutation) and hereditary retinoblastoma (RB1 mutation) **High-Yield:** The classic triad of osteosarcoma imaging is **sunburst periosteal reaction + Codman triangle + cortical breakthrough**. **Clinical Pearl:** Osteosarcoma typically presents in adolescents during growth spurts; any adolescent with metaphyseal bone pain and swelling warrants urgent imaging and oncology referral. ### Prognosis & Management - 5-year survival: ~70% with neoadjuvant chemotherapy + surgical resection - Pulmonary metastases present in ~20% at diagnosis - MRI essential for surgical planning (assess soft tissue involvement and skip lesions)
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