A 16-year-old boy presents with a painful swelling around the distal femur for 2 months. MRI shows an intramedullary lesion with soft tissue extension breaching the cortex. Biopsy reveals high-grade spindle cells producing osteoid. According to the Enneking staging system, what stage is this tumor?
- A Stage IA (low grade, intracompartmental)
- B Stage IIB (high grade, extracompartmental) ✓
- C Stage IIA (high grade, intracompartmental)
- D Stage IIIB (any grade, extracompartmental with metastases)
Correct answer: B. Stage IIB (high grade, extracompartmental)
Explanation
Enneking staging for malignant bone tumors: Stage I = low grade, Stage II = high grade; subtype A = intracompartmental, subtype B = extracompartmental; Stage III = any grade with regional or distant metastases. This high-grade osteosarcoma has breached the cortex and extended into soft tissue, making it extracompartmental — Stage IIB. Osteosarcoma is by definition high grade (G2), so Stage IIA would require the lesion to be confined within the bony cortex without soft tissue extension.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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