High Yield Overview
Tumour Imaging: ABCDS Approach
—Bone Metastases
—Most common malignant bone tumour
—Primary Bone Tumour
—Osteosarcoma most common primary
—MRI Sensitivity
90%Greater than for marrow involvement
—Biopsy Track
—Must be in line with resection
Lodwick Classification
Type IA: Geographic, sclerotic margin
Type IB: Geographic, well-defined, no sclerosis
Type IC: Geographic, ill-defined margin
Type II: Moth-eaten pattern
Type III: Permeative pattern
Key: Higher grade = more aggressive behaviour
Critical Must-Knows
- ABCDS: Age, Border, Cortex, Depth, Soft tissue
- Zone of transition: narrow (benign) vs wide (aggressive)
- Lodwick classification grades aggressiveness (I-III)
- Whole bone MRI mandatory before biopsy for staging
- Biopsy track must be planned with definitive surgeon
Examiner's Pearls
- "Age is single most important factor in differential
- "Periosteal reaction: solid (benign) vs interrupted (aggressive)
- "Skip lesions: separate tumour foci in same bone
- "Enneking staging: compartmental vs extracompartmental
- "Don't biopsy before discussing with tumour surgeon
Exam Warning
Tumour imaging is a favourite viva topic. You MUST know the ABCDS systematic approach, Lodwick classification, and age-related differentials. Always mention that biopsy track planning requires discussion with the definitive tumour surgeon.
ABCDS Systematic Approach
Click to expand
Mnemonic
A-B-C-D-SABCDS - Tumour Imaging Assessment
A
A = Age of patient (most important factor)
B
B = Border/Zone of transition
C
C = Cortex (intact, expanded, destroyed)
D
D = Depth in bone (medullary, cortical, surface)
S
S = Soft tissue mass
Memory Hook:Work through each element systematically in viva - this demonstrates methodical approach and covers all key features
Common Bone Tumours by Age
| Age Group | Benign | Malignant |
|---|---|---|
| Less than 10 years | Eosinophilic granuloma, Simple bone cyst, Osteochondroma | Ewing sarcoma, Neuroblastoma mets |
| 10-30 years | Osteoid osteoma, Chondroblastoma, Aneurysmal bone cyst | Osteosarcoma, Ewing sarcoma |
| 30-40 years | Giant cell tumour, Enchondroma | Primary lymphoma, Parosteal osteosarcoma |
| Greater than 40 years | Fibrous dysplasia (monostotic), Haemangioma | Metastases, Myeloma, Chondrosarcoma |
| Greater than 60 years | Paget's disease | Metastases (most common), Myeloma |
Key Age Rule
In patients over 40, metastases are the most common malignant bone lesion by far. In patients under 30, primary bone tumours are more common than metastases.
Lodwick Classification
Lodwick Classification of Bone Lesions
| Type | Pattern | Zone of Transition | Growth Rate | Typical Lesions |
|---|---|---|---|---|
| IA | Geographic with sclerotic rim | Very narrow | Very slow | NOF, Enchondroma, SBC |
| IB | Geographic without sclerosis | Narrow | Slow | GCT, ABC, Eosinophilic granuloma |
| IC | Geographic with ill-defined margin | Wide | Moderate | Low-grade malignancy, Infection |
| II | Moth-eaten | Wide | Fast | Aggressive malignancy, Osteomyelitis |
| III | Permeative | Very wide | Very fast | Round cell tumours, Ewing, Lymphoma |
Lodwick Clinical Application
Type I lesions (A/B/C) can often be observed or treated conservatively. Type II/III lesions require urgent investigation and often indicate malignancy or aggressive infection. The classification helps predict biological behaviour.
Periosteal Reaction Patterns
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Types of Periosteal Reaction
| Pattern | Appearance | Implication | Common Causes |
|---|---|---|---|
| Solid/continuous | Smooth, uninterrupted | Slow-growing, benign | Stress fracture, Osteoid osteoma |
| Lamellated (onion-skin) | Multiple parallel layers | Intermittent growth | Ewing sarcoma, Osteomyelitis |
| Spiculated (sunburst) | Perpendicular striations | Aggressive, rapid growth | Osteosarcoma |
| Hair-on-end | Fine perpendicular spicules | Aggressive | Ewing, Marrow expansion |
| Codman triangle | Interrupted periosteum lifted at edge | Very aggressive | Osteosarcoma, Ewing, Infection |
Mnemonic
Solid = Slow, Spiculated = SinisterAggressive vs Non-aggressive Periosteal Reaction
S
Solid, continuous periosteum = benign/slow process
I
Interrupted periosteum = aggressive/rapid
C
Codman triangle = aggressive lifting of periosteum
S
Sunburst = tumour outgrowing containment
Memory Hook:Infection can mimic aggressive tumour periosteal reaction - always correlate with clinical features
Matrix Mineralisation
Tumour Matrix Patterns
| Matrix Type | Appearance | Tumours |
|---|---|---|
| Osteoid (bone) | Dense, cloud-like, amorphous | Osteosarcoma, Osteoid osteoma, Osteoblastoma |
| Chondroid (cartilage) | Rings and arcs, popcorn | Enchondroma, Chondrosarcoma, Chondroblastoma |
| Fibrous | Ground-glass, hazy | Fibrous dysplasia, NOF |
| Mixed | Combination patterns | Dedifferentiated tumours |
Chondroid Matrix Key
'Rings and arcs' or 'popcorn' calcification is pathognomonic of cartilage tumours. Seen in both benign (enchondroma) and malignant (chondrosarcoma) cartilage lesions.
Osteoid Matrix Key
Cloud-like, amorphous, dense mineralisation indicates bone formation by tumour. When seen with aggressive features = osteosarcoma until proven otherwise.
MRI in Tumour Imaging
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MRI Staging Requirements
| Assessment | Sequence | Key Information |
|---|---|---|
| Intramedullary extent | T1, STIR | Low T1 = tumour replacing marrow |
| Soft tissue mass | T2, Gd-enhanced | Size, relationship to NV structures |
| Skip lesions | Whole bone T1/STIR | Separate tumour foci (staging, prognosis) |
| Joint involvement | All sequences | Affects surgical planning |
| Neurovascular encasement | Gd-enhanced, MRA | Resectability assessment |
Whole Bone MRI
MANDATORY before biopsy to identify skip lesions. Skip lesions are found in 3-25% of osteosarcomas and significantly affect prognosis and surgical planning.
Classic Tumour Appearances
Classic Benign Bone Tumour Features
| Tumour | Location | Age | Classic Features |
|---|---|---|---|
| Osteoid osteoma | Cortex of long bones | 10-25y | Less than 1.5cm nidus with reactive sclerosis, nocturnal pain relieved by NSAIDs |
| Osteochondroma | Metaphysis, away from joint | Less than 30y | Cortex and medulla continuous with parent bone, pedunculated or sessile |
| Enchondroma | Hands, metaphysis long bones | 20-40y | Central, rings and arcs calcification, Lodwick IA |
| Giant Cell Tumour | Epiphysis, extends to subchondral | 20-40y | Eccentric, subarticular, no sclerotic margin (IB), closed physis |
| Simple Bone Cyst | Proximal humerus, prox femur | Less than 20y | Central, fallen fragment sign, slightly expansile |
| NOF/Fibrous cortical defect | Metaphysis, eccentric | Less than 20y | Well-defined, sclerotic rim, asymptomatic, resolves |
Soft Tissue Tumour Imaging
Soft Tissue Tumour Imaging Features
| Feature | Benign Indicators | Malignant Indicators |
|---|---|---|
| Size | Less than 5 cm | Greater than 5 cm |
| Location | Superficial to fascia | Deep to fascia |
| Margins | Well-defined, smooth | Irregular, infiltrative |
| Growth pattern | Homogeneous | Heterogeneous, necrosis |
| Signal characteristics | Homogeneous signal | Mixed signal, haemorrhage, necrosis |
| Enhancement | Uniform or none | Heterogeneous, peripheral |
Soft Tissue Sarcoma Size Rule
Any deep soft tissue mass greater than 5cm warrants urgent specialist referral and staging MRI before biopsy. Deep location, large size, and rapid growth are red flags.
Imaging-Guided Biopsy
Pre-Biopsy Requirements
Complete staging imaging BEFORE biopsy. Whole bone MRI (skip lesions). CT chest for lung metastases. Discuss biopsy track with tumour surgeon. Plan track in line with definitive resection.
Biopsy Principles
Shortest path through normal tissue. Avoid contaminating uninvolved compartments. Mark skin entry site for excision. Core biopsy preferred over open when possible. Haemostasis critical.
Mnemonic
Track in LineBiopsy Planning
T
Track must be planned for en bloc resection
I
In consultation with tumour surgeon
L
Line of approach through eventual incision site
Memory Hook:Poorly planned biopsy can convert a limb-salvage case to amputation due to track contamination
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
EXAMINER
"A 16-year-old presents with a 2-month history of knee pain. X-ray shows a mixed lytic and sclerotic lesion in the distal femoral metaphysis with periosteal reaction."
EXCEPTIONAL ANSWER
Using ABCDS: Age (A) - 16 years old, peak age for osteosarcoma and Ewing sarcoma. Border (B) - would assess zone of transition; if wide with ill-defined margins suggests aggressive lesion. Cortex (C) - need to assess for destruction or intact cortex. Depth (D) - metaphyseal location typical for osteosarcoma. Soft tissue (S) - need to look for associated soft tissue mass. The periosteal reaction pattern is key - sunburst or Codman triangle suggests osteosarcoma; onion-skin might suggest Ewing. My primary differential in this age group with metaphyseal location is osteosarcoma until proven otherwise.
KEY POINTS TO SCORE
Systematic ABCDS approach demonstrates methodology
Age 16 + metaphysis + aggressive features = osteosarcoma likely
Periosteal reaction pattern helps differentiate
Requires urgent MRI staging before biopsy
CT chest for pulmonary metastases
COMMON TRAPS
✗Jumping to diagnosis without systematic approach
✗Ordering biopsy before staging imaging
✗Not referring to tumour centre urgently
VIVA SCENARIOStandard
EXAMINER
"A 55-year-old woman presents with back pain. Spinal X-ray shows a lytic lesion in L3 vertebral body. She has a history of breast cancer 5 years ago."
EXCEPTIONAL ANSWER
In a 55-year-old with history of breast cancer, the primary differential is metastatic disease until proven otherwise. Metastases are the most common malignant bone tumour in this age group. Other considerations include myeloma (punched-out lytic lesions), and less likely primary bone tumour. Investigation: Blood tests (Ca, ALP, PSA if male, myeloma screen), MRI spine (extent, other lesions, soft tissue), CT chest/abdomen/pelvis (primary/other sites), bone scan or PET-CT (whole body staging). Biopsy if diagnosis uncertain after imaging.
KEY POINTS TO SCORE
Over 40 years: metastases most common malignant lesion
Breast, prostate, lung, kidney, thyroid = common primaries
Vertebral body involvement favours metastases (cf pedicle = infection)
Myeloma screen essential in elderly with lytic lesions
PET-CT useful for whole body staging
COMMON TRAPS
✗Assuming new primary tumour in someone with cancer history
✗Not performing myeloma screen
✗Missing cord compression on imaging
VIVA SCENARIOStandard
EXAMINER
"A 30-year-old presents with hip pain. X-ray shows an expansile lytic lesion in the proximal tibial epiphysis extending to the subchondral bone. The lesion has no sclerotic margin."
EXCEPTIONAL ANSWER
The most likely diagnosis is Giant Cell Tumour (GCT). Classic features present: Age 20-40 years (peak 30), epiphyseal location extending to subchondral bone (virtually pathognomonic), eccentrically placed, expansile lytic lesion, no sclerotic rim (Lodwick IB), and importantly occurring after skeletal maturity (closed physis). GCT is locally aggressive but rarely metastasises (2% lung). MRI will show the extent and any soft tissue component. Treatment is usually curettage with adjuvant and bone grafting or cementation.
KEY POINTS TO SCORE
GCT: 20-40 years, eccentric, epiphyseal, subchondral
Must have closed physis (mature skeleton)
No sclerotic margin (Lodwick IB)
50% around the knee (distal femur, proximal tibia)
Rarely metastasises (lung)
COMMON TRAPS
✗Diagnosing GCT with open physis (wrong - need mature skeleton)
✗Missing the subchondral extension (key feature)
✗Confusing with ABC (ABC can occur in epiphysis but usually has fluid-fluid levels on MRI)
Tumour Imaging ABCDS Approach
High-Yield Exam Summary
ABCDS Framework
- •Age: Most important factor - metastases if greater than 40
- •Border: Narrow = benign, Wide = aggressive
- •Cortex: Intact/expanded vs destroyed
- •Depth: Medullary/cortical/surface location
- •Soft tissue: Mass indicates aggressive behaviour
Lodwick Classification
- •IA: Geographic + sclerotic rim = very benign
- •IB: Geographic, well-defined = slow growing
- •IC: Geographic, ill-defined = moderate
- •II: Moth-eaten = aggressive
- •III: Permeative = very aggressive (Ewing, lymphoma)
Periosteal Reaction
- •Solid/continuous = slow, benign
- •Lamellated (onion-skin) = Ewing, infection
- •Sunburst = osteosarcoma
- •Codman triangle = aggressive
Pre-Biopsy Rules
- •Whole bone MRI BEFORE biopsy (skip lesions)
- •CT chest for lung metastases
- •Discuss track with tumour surgeon
- •Plan track in line with definitive resection
- •Poor biopsy can convert salvage to amputation