Radiology · Year 4 · from Radiology

Case 3: Osteosarcoma

Patient Demographics

  • Age: 16 years
  • Sex: Male

Chief Complaint

Progressive left knee pain for 3 months

Presenting Symptoms

The patient reports gradual onset of left knee pain that began approximately 3 months ago. Initially, he attributed it to a minor injury during soccer practice. The pain has progressively worsened and is now present at rest and at night, disturbing his sleep. He has noticed swelling above his left knee. He denies fevers, weight loss, or other joint involvement. No history of prior malignancy or radiation exposure.

Physical Exam Findings

  • Vital Signs: Within normal limits
  • Left Knee/Distal Thigh:
  • Firm, fixed mass palpable in the distal anterior thigh/suprapatellar region
  • Overlying warmth and prominent superficial veins
  • Tenderness to palpation over the mass
  • Mild knee effusion
  • Knee range of motion mildly limited by pain
  • No erythema or skin breakdown
  • Lymph Nodes: No palpable inguinal lymphadenopathy
  • Systemic: No hepatosplenomegaly, no other masses

Imaging Findings and Interpretation

Knee Radiographs (AP and Lateral):

Aggressive Features:

  • Location: Distal femoral metaphysis - classic location for osteosarcoma
  • Bone Destruction: Mixed lytic and scite pattern with permeative margins
  • Periosteal Reaction:
  • Aggressive "sunburst" pattern (spiculated periosteal new bone radiating perpendicular to cortex)
  • Codman triangle (elevated periosteum at lesion margin)
  • Tumor Matrix: Cloud-like osteoid matrix production within the tumor (tumor bone)
  • Soft Tissue Mass: Extension beyond the cortex with soft tissue component
  • Cortical Destruction: Disruption of the lateral femoral cortex
  • No Pathologic Fracture: Cortex thinned but no complete fracture

Zone of Transition: Wide and poorly defined - aggressive feature

MRI Left Femur (Staging):

  • Tumor Extent:
  • Intramedullary tumor length: 12 cm
  • Involvement of distal femoral metaphysis and extends into diaphysis
  • Epiphysis: Tumor approaches but does not cross the growth plate
  • Soft Tissue Component: 6 x 5 x 8 cm heterogeneous mass with areas of necrosis and hemorrhage
  • Neurovascular Structures: Popliteal vessels displaced but not encased; appears resectable
  • Skip Lesions: None identified in the femur
  • Joint Involvement: No definite invasion of knee joint

CT Chest (Metastatic Workup):

  • Multiple small bilateral pulmonary nodules (largest 8mm)
  • Consistent with pulmonary metastases
  • No mediastinal lymphadenopathy

Bone Scan/PET-CT:

  • Intense uptake in distal left femur primary
  • Multiple pulmonary metastases with FDG avidity
  • No other skeletal lesions

Diagnosis

Osteosarcoma of the distal femur with pulmonary metastases (Stage IVB); confirmed on biopsy: High-grade conventional osteosarcoma

Management

  1. Multidisciplinary Tumor Board:
  • Pediatric oncology, orthopedic oncology, thoracic surgery, radiology, pathology
  1. Biopsy:
  • Image-guided core biopsy performed with tract planning for future resection inclusion
  • Histology: High-grade conventional osteosarcoma with osteoid production
  1. Neoadjuvant Chemotherapy:
  • MAP regimen (Methotrexate, Doxorubicin/Adriamycin, Cisplatin)
  • 10-12 weeks prior to surgery
  • Monitor response with MRI
  1. Surgical Resection:
  • Limb salvage surgery with wide resection and endoprosthetic reconstruction
  • Pathology: 85% tumor necrosis (good response to chemotherapy)
  • Margins negative
  1. Metastasectomy:
  • Thoracoscopic resection of pulmonary metastases
  1. Adjuvant Chemotherapy:
  • Continue MAP regimen post-operatively
  1. Surveillance:
  • Chest CT every 3 months for 2 years, then every 6 months
  • Local MRI every 3-6 months
  • Functional assessment and prosthesis evaluation

Radiological Image

Image Description: Radiograph of the distal femur demonstrating osteosarcoma with characteristic aggressive features including the "sunburst" periosteal reaction (spiculated new bone radiating perpendicular to the cortex), Codman triangle (elevated periosteum at the tumor margin), tumor matrix ossification, and soft tissue mass extending beyond the destroyed cortex.

Source: Wikimedia Commons - "Osteosarcoma radiograph" URL: https://commons.wikimedia.org/wiki/File:Osteosarcoma_-_high_mag.jpg License: Creative Commons Attribution-Share Alike 3.0 Unported

Learning Points

  1. Colles Fracture Characteristics: The classic distal radius fracture pattern with dorsal displacement, dorsal angulation, and radial shortening. Post-reduction radiographs should demonstrate restored radial inclination (>15 degrees), volar tilt (0-15 degrees), and radial length. Fragility fractures warrant osteoporosis evaluation.
  1. ACL Tear Imaging: MRI is the gold standard for diagnosing ACL tears. Associated findings include "kissing contusions" of the lateral femoral condyle and posterolateral tibial plateau, Segond fracture (pathognomonic), and lipohemarthrosis on radiographs.
  1. Aggressive vs. Benign Bone Lesion Features:
  • Aggressive: Wide zone of transition, permeative destruction, aggressive periosteal reaction (sunburst, Codman triangle), soft tissue mass
  • Benign: Narrow zone of transition, sclerotic margins, solid periosteal reaction, no soft tissue mass
  1. Osteosarcoma Imaging Approach: Radiographs identify the lesion and suggest aggressiveness. MRI determines local extent and surgical planning. CT chest evaluates for pulmonary metastases. Bone scan or PET-CT screens for skeletal metastases and skip lesions.

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