A 16-year-old boy presents with a 6-week history of progressive pain and swelling around the right knee. On examination, there is a firm, tender mass over the distal femur with overlying skin warmth. Plain radiographs show a mixed lytic-sclerotic lesion at the metaphysis with periosteal new bone formation (Codman's triangle). Serum alkaline phosphatase is elevated at 180 IU/L. What is the most appropriate next step in management?

Explanation

## Clinical Presentation & Diagnosis The clinical and radiological findings are classic for osteosarcoma: - Age 16 (peak incidence 10–25 years) - Metaphyseal location at the distal femur (most common site) - Mixed lytic-sclerotic lesion with Codman's triangle (periosteal reaction) - Elevated alkaline phosphatase (reflects osteoid production) **Key Point:** Osteosarcoma is the most common primary malignant bone tumor in children and young adults. Diagnosis is primarily radiological; biopsy is NOT the first step in management. ## Management Algorithm for Osteosarcoma ```mermaid flowchart TD A[Clinical + XR findings suggestive of osteosarcoma]:::outcome --> B[MRI of primary site + Chest CT]:::action B --> C{Staging complete?}:::decision C -->|Yes| D[Neoadjuvant chemotherapy]:::action D --> E[Surgical resection]:::action E --> F[Adjuvant chemotherapy]:::action F --> G[Long-term follow-up]:::outcome ``` ## Why MRI + Chest CT First? | Investigation | Purpose | Timing | |---|---|---| | **MRI of primary** | Assess soft tissue extension, neurovascular involvement, surgical margins | Before chemotherapy | | **Chest CT** | Detect pulmonary metastases (present in ~20% at diagnosis) | Before chemotherapy | | **Biopsy** | Histological confirmation | After imaging, if diagnosis uncertain | **High-Yield:** Modern osteosarcoma management follows a multimodal approach: neoadjuvant chemotherapy → surgical resection → adjuvant chemotherapy. Neoadjuvant therapy improves survival by: 1. Reducing primary tumor size and vascularity 2. Allowing time for surgical planning 3. Treating micrometastases 4. Assessing histological response (prognostic indicator) **Clinical Pearl:** Immediate surgical excision without staging and neoadjuvant therapy is outdated and reduces overall survival. Chemotherapy is essential even though osteosarcoma is a solid tumor. ## Why This Sequence? 1. **MRI** defines local extent and surgical feasibility 2. **Chest CT** identifies pulmonary metastases (most common site) 3. **Neoadjuvant chemotherapy** is standard of care and improves 5-year survival from ~20% to ~65–70% 4. Surgery is deferred until after imaging and initial chemotherapy **Tip:** Remember the acronym **MACS** for osteosarcoma management: **M**RI, **A**djuvant/neoadjuvant chemotherapy, **C**hest imaging, **S**urgery.