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Imaging of Bone Tumors - Detailed Explanation

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1. The Systematic Radiological Approach (Enneking's Four Questions)

1. Location - Where is the lesion (epiphysis, metaphysis, diaphysis; intramedullary, intracortical, surface)?
2. Tumor-bone interaction - How is the tumor destroying bone (Lodwick classification)?
3. Bone-tumor interaction - How is the host bone responding?
4. Matrix - What are the tumor cells producing (bone, cartilage, fibrous tissue)?

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2. Age of the Patient

• Miller's Review of Orthopaedics 9th Edition

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3. Plain Radiograph - Rate of Growth & Lodwick Classification (Tumor-Bone Interaction)

Type I - Geographic (Slow Growth / Benign or Low-Grade)

• Type IA: Well-defined lytic lesion with a sclerotic rim (e.g., nonossifying fibroma, osteoid osteoma)
• Type IB: Well-defined lytic lesion with no marginal sclerosis (e.g., unicameral bone cyst)
• Type IC: Slightly less sharp, non-sclerotic margin (e.g., giant cell tumor)

Type II - Moth-Eaten (Moderately Aggressive)

• Multiple lucent areas 2-5 mm in diameter separated by intact trabeculae
• Examples: Osteomyelitis, metastases, lymphoma

Type III - Permeative/Destructive (Most Aggressive)

• Multiple coalescing tiny ill-defined lesions ≤1 mm in diameter
• Wide zone of transition spanning several centimeters
• Example: Ewing sarcoma
• Radiographs underestimate medullary involvement; MRI is essential
• Grainger & Allison's Diagnostic Radiology, Miller's Review of Orthopaedics 9th Edition

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4. Periosteal Reaction

• Grainger & Allison's Diagnostic Radiology, Campbell's Operative Orthopaedics 15th Ed.

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5. Anatomical Location Within the Bone

• Lesions distal to the elbow and knee are usually from lung or renal primaries when metastatic
• Myeloma: spine and ribs most common
• Chordoma: exclusively at ends of the vertebral column (sacrum/clivus)
• Miller's Review of Orthopaedics 9th Edition

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6. Matrix Characterization on Radiograph

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7. Number of Lesions

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8. Modality-by-Modality Role

Plain Radiograph (X-ray)

• First-line always - defines lesion type, location, periosteal reaction, matrix
• Two planes mandatory
• Underestimates medullary extent

Computed Tomography (CT)

• Better than X-ray for infection detection; MRI is still more sensitive
• Confirms benign appearance of enchondroma, osteochondroma, bone island (enostosis)
• Best modality for osteoid osteoma - the nidus is better visualized on CT and can be misleading on MRI
• Precisely delineates calcifications, mineralization, cortical integrity, periosteal reaction (MDCT)
• Does not show soft tissue characteristics or medullary canal extent as well as MRI
• Used when MRI is contraindicated (pacemaker, metallic foreign bodies) or unavailable
• 3D CT for preoperative planning

MRI

• Most sensitive for evaluating bone lesions
• Should encompass the entire bone when evaluating primary bone tumors (to exclude skip metastases)
• Best for soft tissue extension, neurovascular involvement, medullary canal extent
• Guides surgical planning and limb-salvage decisions
• Guides biopsy site selection

Bone Scan (Tc-99m)

• Whole-body - identifies occult polyostotic bone involvement
• Useful for staging and detecting skip lesions
• Cold scan in myeloma (false negative) - skeletal survey is more sensitive for myeloma
• Useful in protracted back pain / night pain (spinal tumors)

PET/CT

• Whole-body staging for metastatic disease
• Evaluates metabolic activity - useful for treatment response assessment

Whole-body MRI

• Used in assessment of metastases from myxoid liposarcoma specifically
• Increasingly used for myeloma staging
• Rockwood & Green's Fractures 10th Ed., Miller's Review of Orthopaedics 9th Edition, Grainger & Allison's Diagnostic Radiology

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9. Specific Tumor Imaging Signatures

Osteosarcoma

• Metaphysis of long bones (distal femur > proximal tibia > proximal humerus)
• Aggressive mixed lytic/sclerotic lesion with sunburst periosteal reaction and Codman's triangle
• Soft tissue mass with tumor bone formation
• MRI: entire bone should be imaged to identify skip metastases
• CT chest for pulmonary metastases (most common site)

Ewing Sarcoma

• Diaphysis of long bones; flat bones (pelvis, ribs, scapula)
• Onion-skin (laminated) periosteal reaction on X-ray; Codman's triangle
• Permeative bone destruction (Lodwick type III)
• MRI: massive soft tissue mass disproportionate to the degree of bone destruction - characteristic finding
• Bone scan for staging

Giant Cell Tumor (GCT)

• Epiphysis of long bones in skeletally mature patients (distal femur, proximal tibia, distal radius)
• Lodwick type IC: lytic, geographic, eccentric, subarticular, NO sclerotic margin
• No matrix mineralization
• "Soap bubble" appearance of expanded cortex
• MRI: T1 low, T2 intermediate-high signal; well-defined margins

Chordoma

• Exclusively at ends of vertebral column: sacrum (50%), clivus (35%), vertebral bodies (15%)
• Radiographs underestimate true extent
• MRI: midline bone destruction + soft tissue mass; T1 low, T2 very bright signal; sacrum often expanded with irregular mineralization

Aneurysmal Bone Cyst (ABC)

• Metaphysis of long bones; posterior elements of spine
• Eccentric lytic expansile lesion with "eggshell" cortex
• MRI hallmark: fluid-fluid levels on T2 (layering of blood products at different stages)

Enchondroma

• Small bones of hands/feet most common; also proximal humerus, femur
• Stippled or "rings and arcs" chondroid calcification
• Benign appearance confirmed on CT; no cortical destruction, no soft tissue mass

Osteochondroma

• Sessile or pedunculated bony outgrowth with cartilage cap
• Cortex and medullary canal continuous with host bone
• MRI cartilage cap thickness: > 2 cm in adults raises concern for malignant transformation to chondrosarcoma

Multiple Myeloma

• "Punched-out" lytic lesions - no host bone response (no sclerotic margin, no periosteal reaction)
• "Ballooned" appearance with expansion in advanced disease
• Spine and ribs most common
• Whole-body low-dose CT or PET/CT now preferred over skeletal survey

Lymphoma of Bone

• Minimal bone destruction on plain film despite large soft tissue mass
• MRI T2: massive soft tissue mass disproportionate to the minimal cortical destruction - characteristic
• Older patients (>30 years); CD45+, CD20+ markers

Vertebral Hemangioma

• Vertical striations ("corduroy cloth") or honeycomb coarsened trabecular pattern on X-ray
• Typical location: vertebral body
• Usually incidental; symptomatic lesions may be treated

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10. Blue Cell Tumors - Imaging Comparison (Mnemonic: LERNM - "Learn 'em")

• Miller's Review of Orthopaedics 9th Edition

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11. Staging of Bone Sarcomas (Enneking / AJCC)

• Harrison's Principles of Internal Medicine 22E

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12. Summary Algorithm

Bone lesion detected
       ↓
Plain X-ray (2 views) → Apply Lodwick, assess periosteum, matrix, location, age
       ↓
Is it likely benign? ──Yes──> CT to confirm (enchondroma, osteochondroma, bone island)
       ↓ No
MRI of entire bone → Extent of medullary involvement, soft tissue mass, skip lesions
       ↓
Tc-99m bone scan → Polyostotic disease? Skip lesions?
       ↓
CT chest/abdomen/pelvis or PET/CT → Metastatic staging
       ↓
Biopsy (guided by imaging, through single compartment, longitudinal incision)

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• Grainger & Allison's Diagnostic Radiology, Chapter 40 (Bone Tumors)
• Miller's Review of Orthopaedics 9th Ed., Section 9 (Musculoskeletal Oncology)
• Harrison's Principles of Internal Medicine 22E, Chapter 96 (Bone Sarcomas)
• Rockwood & Green's Fractures in Adults 10th Ed., Chapter on Infection and Bone Tumor Workup
• Campbell's Operative Orthopaedics 15th Ed., Chapters 10, 11, 23, 83