Imaging Bone Tumours

Imaging Modalities

• X-Ray - initial detection and characterization
• CT Scan - detailed bone architecture and characterization
• MRI - local staging, soft tissue involvement
• Bone Scan - detection of bone metastases
• PET-CT - metabolic activity and systemic staging

Imaging Strategy

1. Detection & Characterization (X-rays, CT scan)
2. Local staging (MRI)
3. Systemic staging - evaluation for regional and distant metastases (CT chest, bone scan, PET scan)

X-Ray Interpretation: The 7 Key Features

1. Site - bone and location within bone
2. Size - dimensions of the lesion
3. Matrix - internal composition and calcification patterns
4. Pattern/Margins - including zone of transition
5. Effect of the lesion on bone - cortical changes
6. Reaction of bone to the lesion - periosteal response
7. Soft tissue mass - presence or absence

Site Analysis

• Which bone is affected (femur, radius, etc.)
• Location within bone:
  • Diaphysis, metaphysis, epiphysis, or combination
  • Centric, eccentric, intracortical, surface

Matrix Analysis

• Fibrous, fluid, fat (radiolucent; dark demarcations)
• Cartilaginous (arcs and rings of calcification)
• Osseous (cloud-like, dense)
• Mixed patterns

Bubbly Cloudy

Benign vs Malignant: Pattern Recognition

Destruction Patterns

Benign Process

• Geographic - uniformly destroyed area with sharply defined border

Likely Malignant Process

• Moth-eaten - areas of destruction with ragged borders

Aggressive/Malignant Process

• Permeative - ill-defined area spreading through marrow space

Zone of Transition

- Mixed

- Ill-defined

Lesion Effects on Bone

Cortical Changes

• Cortical thinning ✓ Lower grade, less aggressive

• Cortical expansion ✓ Low or high grade, tumor mimickers

• Cortical destruction ✓ High grade, aggressive

Bone Reaction to Lesion

Periosteal Reaction Patterns

• Absent - typically benign lesions
• Mild – one layer, 1-4 mm thick, adjacent to cortex
• Major - >5mm, multilayered or lamellated:
  • “Onion-skimming”
  • “Hair-on-end”
  • “Sunburst”

Codman’s triangle- causes include infections / tumours

Soft Tissue Mass Assessment

• Absent - suggests benign process
• Present - raises concern for malignancy

Differential Diagnosis by Bone Location

Diaphysis

Characteristic lesions:

• Adamantinoma
• Osteofibrous Dysplasia
• Osteoid Osteoma
• Stress Fracture
• Chronic Osteomyelitis
• Round Cell Tumors (Ewing sarcoma, Lymphoma)
• Langerhans Cell Histiocytosis
• Fibrous Dysplasia
• Fibrous Cortical Defect / Non-ossifying Fibroma

Metaphysis

Characteristic lesions:

• Osteochondroma
• Osteosarcoma
• Fibrosarcoma
• Chondromyxoid Fibroma
• Aneurysmal Bone Cyst
• Enchondroma / Chondrosarcoma
• Simple Bone Cyst
• Fibrous Dysplasia
• Osteomyelitis (pyogenic)

Epiphysis

Characteristic lesions:

• Articular Osteochondroma (Trevor Disease)
• Chondroblastoma (children)
• Giant Cell Tumor (adults)
• Osteomyelitis (fungal, TB)
• Aneurysmal Bone Cyst
• Clear cell chondrosarcoma

Intra-articular Tumors

• Pigmented Villonodular Synovitis (PVNS)
• Synovial Hemangioma
• Intra-articular Loose Bodies

Epiphyseal Lesions: Detailed Analysis

Common Epiphyseal Tumors

• Chondroblastoma

• Clear cell chondrosarcoma

• Osteomyelitis (occasionally)

• Chondroblastoma

Apophyseal Lesions

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Epiphyseal-Metaphyseal Lesions

Benign aggressive lesions:

• Giant Cell Tumor (GCT)
• Aneurysmal Bone Cyst (ABC)
• Osteoblastoma

Giant Cell Tumor

Aneurysmal Bone Cyst

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Metaphyseal Lesions: Detailed Examples

Common Metaphyseal Tumors

• Enchondroma
• Simple Bone Cyst (SBC)
• Non-ossifying Fibroma (NOF) / Fibrous cortical defect
• Chondromyxoid fibroma
• Osteosarcoma
• Chondrosarcoma

Simple Bone Cyst

Other Metaphyseal Lesions

Popcorn, cartilaginous - chondrosarcoma usually - even though theres no perosteal reaction

site: distal femur size: Most (involving how much? / cm?) matrix: mixed - mainly radiopaque , wide zone of transition, cortical destruction, resulted periosteal reaction, and codman’s triangle soft tissue involvement:

Non-ossifying Fibroma

site: Diaphyseal, metaphysal size: partial matrix: Mixed - Narrow zone of transition, well defined, syndosmosis soft tissue involvement: No tissue involvement

Aneurysmal Bone Cyst

site: Distal tibial size: Involving most of distal part matrix: Cortical expansion, radiolucent matrix, well defined, narrow zone of transition soft tissue involvement: no peristeal reaction

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site: Distal shaft of femur size: matrix: Opaque, well defined, ossifying fibroma soft tissue involvement: no peristeal reaction

site: Distal femur size: matrix: soft tissue involvement:

Diaphyseal Lesions: Detailed Examples

Common Diaphyseal Tumors

• Osteoid osteoma
• Fibrous dysplasia
• Osteofibrous dysplasia
• Adamantinoma
• Ewing’s sarcoma

Osteoid Osteoma

Thick cortex

Other Diaphyseal Lesions

Could be malignant, even though no periosteal reaction, may be due old fracture

Pathological fracture, after metastasis

Important Diagnostic Note

Always remember infection as differential diagnosis