High Yield Overview
Classic Radiological Signs: Tumours
—Lodwick Grades
—IA to III
—Skip Lesions
—Osteosarcoma, Ewing's
—Codman Triangle
—Aggressive periosteal
—Soap Bubble
—GCT, ABC
Lodwick Classification
IA: Geographic, sclerotic margin (benign)
IB: Geographic, defined margin (slow-growing)
IC: Geographic, ill-defined (moderate aggression)
II: Moth-eaten (aggressive)
III: Permeative (highly aggressive)
Key: Higher Lodwick grade = more aggressive behaviour
Critical Must-Knows
- Lodwick classification predicts biological behaviour
- Codman triangle = aggressive (not diagnostic of malignancy)
- Sunburst/hair-on-end = osteosarcoma, Ewing's
- Soap bubble appearance = GCT, ABC, chondroblastoma
- Ground glass = fibrous dysplasia pathognomonic
Examiner's Pearls
- "Matrix calcification: Rings and arcs = cartilage, cloud-like = osteoid
- "Fallen fragment sign = unicameral bone cyst
- "Onion skin periosteal reaction = Ewing's sarcoma
- "Bone within bone = metastases, Paget's, osteopetrosis
Clinical Imaging
Imaging Gallery
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Exam Warning
Tumour radiological signs are very commonly examined. Know the Lodwick classification, types of periosteal reaction (organised vs aggressive), matrix patterns, and pathognomonic signs like ground glass (fibrous dysplasia) and fallen fragment (UBC).
Lodwick Classification
Lodwick Classification of Bone Lesions
| Grade | Pattern | Margin | Growth Rate | Examples |
|---|---|---|---|---|
| IA | Geographic | Sclerotic (reactive bone) | Indolent/benign | NOF, enchondroma, UBC |
| IB | Geographic | Well-defined, no sclerosis | Slow | GCT, ABC, chondroblastoma |
| IC | Geographic | Ill-defined, partial cortex loss | Moderate | Low-grade chondrosarcoma |
| II | Moth-eaten | Multiple small holes | Aggressive | Myeloma, lymphoma, metastases |
| III | Permeative | Fine cortical holes, imperceptible | Highly aggressive | Ewing's, infection, round cell |
Clinical Significance
Lodwick classification correlates with biological behaviour: Grade IA/IB typically benign and can be observed, Grade IC requires biopsy to exclude low-grade malignancy, Grade II/III indicates aggressive lesion requiring urgent workup.
Periosteal Reaction Signs
Organised Periosteal Reactions
| Sign | Appearance | Indicates | Examples |
|---|---|---|---|
| Solid periosteal reaction | Single layer of new bone parallel to cortex | Benign/slow process | Healing fracture, osteoid osteoma |
| Lamellated (onion skin) | Multiple parallel layers | Repeated episodes | Chronic infection, Ewing's (can be aggressive) |
| Buttress | Triangular new bone at lesion edge | Contained process | Benign expansile lesions |
Matrix Pattern Signs
Tumour Matrix Patterns
| Matrix Type | Appearance | Indicates | Examples |
|---|---|---|---|
| Chondroid (rings and arcs) | Punctate, curvilinear calcification | Cartilage tumour | Enchondroma, chondrosarcoma |
| Osteoid (cloud-like) | Amorphous, dense, 'cotton wool' | Bone-forming tumour | Osteosarcoma, osteoblastoma |
| Ground glass | Hazy, homogeneous density | Fibrous stroma | Fibrous dysplasia (pathognomonic) |
| No matrix | Purely lytic | Non-matrix producing | Myeloma, metastases, GCT |
Pathognomonic Signs
Classic Tumour Signs
| Sign | Description | Diagnosis |
|---|---|---|
| Ground glass matrix | Hazy, homogeneous 'smoky' appearance | Fibrous dysplasia |
| Fallen fragment sign | Cortical fragment fallen to dependent portion | Unicameral bone cyst |
| Soap bubble appearance | Expansile, multiloculated, trabeculated | GCT, ABC (also chondroblastoma) |
| Nidus with reactive sclerosis | Small lucent nidus with surrounding sclerosis | Osteoid osteoma |
| Donut sign (bone scan) | Peripheral uptake, central photopenia | Enchondroma, benign lesions |
| Ring enhancement (MRI) | Peripheral gadolinium enhancement | Abscess, necrotic tumour |
| Bone within bone | Inner bone outline within outer | Metastases, Paget's, osteopetrosis |
| Flame sign | V-shaped advancing edge in long bone | Paget's disease |
Fallen Fragment Sign
Pathognomonic for unicameral bone cyst (UBC). A fragment of cortex or pathological fracture debris falls to the dependent portion of the cyst cavity due to fluid content. This distinguishes UBC from solid lesions. Best seen on cross-table lateral or CT.
Location-Specific Signs
Classic Tumour Locations
| Location | Classic Tumour | Key Sign |
|---|---|---|
| Epiphysis (skeletally immature) | Chondroblastoma | Eccentric, well-defined, may have calcification |
| Epiphysis (mature) | GCT | Extends to subchondral bone, no sclerosis |
| Metaphysis (central) | Enchondroma, UBC | Matrix calcification (enchondroma), fallen fragment (UBC) |
| Metaphysis (eccentric) | NOF, CMF, ABC | Soap bubble (ABC), cortical-based (NOF) |
| Diaphysis | Ewing's, lymphoma, adamantinoma | Permeative pattern, onion skin |
| Posterior elements spine | ABC, osteoblastoma | Expansile, may have aneurysmal component |
| Vertebral body | Haemangioma, mets, myeloma | Corduroy pattern (haemangioma) |
Mnemonic
CIAOEpiphyseal Lesions Before Closure
C
C = Chondroblastoma (most common)
I
I = Infection
A
A = ABC (aneurysmal bone cyst)
O
O = Osteomyelitis
Memory Hook:After physeal closure, GCT becomes the classic epiphyseal lesion
Mnemonic
SIGNS of Malignancy
S
Skip lesions - Discontinuous tumour spread
Skip lesions - Discontinuous tumour spread
I
Ill-defined margins - Permeative or moth-eaten pattern
Ill-defined margins - Permeative or moth-eaten pattern
G
Gone cortex - Cortical destruction
Gone cortex - Cortical destruction
N
New bone formation - Aggressive periosteal reaction
New bone formation - Aggressive periosteal reaction
S
Soft tissue mass - Extraosseous tumour extension
Soft tissue mass - Extraosseous tumour extension
Memory Hook:SIGNS of malignancy indicate aggressive biological behaviour
Soft Tissue Tumour Signs
Soft Tissue Tumour Signs
| Sign | Description | Differential |
|---|---|---|
| Fat signal on all sequences | Follows subcutaneous fat signal | Lipoma (benign) |
| Blooming artefact | Signal loss on GRE due to haemosiderin | PVNS, haemosiderin-laden tissue |
| Split fat sign | Thin rim of fat around lesion | Benign intramuscular lesion |
| Muscle invasion | Tumour infiltrating between muscle fibres | Aggressive/malignant |
| Tail sign | Linear extension along fascial plane | DFSP, myxofibrosarcoma |
| Phlebolith | Round calcification in vessel | Haemangioma |
| Peripheral nerve connection | Lesion in continuity with nerve | Schwannoma, neurofibroma |
PVNS Blooming
Pigmented villonodular synovitis contains haemosiderin deposits that cause marked signal loss (blooming) on gradient echo (GRE) sequences due to magnetic susceptibility. This is highly characteristic and helps distinguish PVNS from other synovial processes.
Metastatic Disease Signs
Metastatic Disease Patterns
| Sign | Description | Primary Tumours |
|---|---|---|
| Lytic metastases | Purely destructive, moth-eaten/permeative | Lung, renal, thyroid, melanoma |
| Sclerotic metastases | Dense, ivory-like | Prostate, breast, carcinoid |
| Mixed lytic-sclerotic | Combination pattern | Breast (most common) |
| Winking owl sign | Missing pedicle on AP spine | Spinal metastasis |
| Pathological fracture | Fracture through lesion | Any destructive metastasis |
| Superscan | Diffuse uptake, absent kidney/bladder | Widespread skeletal metastases |
| Skip lesions | Non-contiguous same bone | Osteosarcoma, Ewing's (also mets) |
Winking Owl Sign
On AP spinal radiograph, the normal vertebra resembles an owl with the pedicles as 'eyes'. When one pedicle is destroyed by metastasis, the owl appears to be 'winking'. This is an important sign for vertebral metastases on plain film, often before vertebral body collapse is visible.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
EXAMINER
"A 15-year-old presents with knee pain. X-ray shows a lesion in the proximal tibial metaphysis with a 'sunburst' periosteal reaction and cloud-like mineralisation extending into a soft tissue mass."
EXCEPTIONAL ANSWER
The most likely diagnosis is conventional osteosarcoma. Key features: (1) Age group - osteosarcoma peaks in the second decade. (2) Location - metaphysis of long bone around the knee (60% occur here). (3) Sunburst periosteal reaction - aggressive pattern with radiating spicules perpendicular to cortex, indicating rapid periosteal elevation. (4) Osteoid matrix - the cloud-like (amorphous) mineralisation indicates bone-forming tumour. (5) Soft tissue extension - osteoid within the soft tissue mass is characteristic. The combination of metaphyseal location, aggressive periosteal reaction, and osteoid matrix in a teenager is virtually diagnostic of osteosarcoma.
KEY POINTS TO SCORE
Sunburst = aggressive periosteal reaction
Cloud-like matrix = osteoid production
Osteoid in soft tissue mass = osteosarcoma
Peak age 10-20 years
Metaphysis around knee most common
COMMON TRAPS
✗Confusing with Ewing's (no osteoid matrix)
✗Not recognising cloud-like matrix as osteoid
✗Missing soft tissue extension
VIVA SCENARIOStandard
EXAMINER
"A 25-year-old presents with wrist pain. X-ray shows an eccentric, lytic lesion in the distal radius extending to the subchondral bone, with no sclerotic margin and no matrix calcification."
EXCEPTIONAL ANSWER
This is most likely a giant cell tumour (GCT). Characteristic features: (1) Age - GCT occurs after skeletal maturity (20-40 years peak). (2) Location - epiphyseal/metaphyseal extending to subchondral bone (GCT 'likes to touch the joint'). (3) Eccentric position - typically arises eccentrically in the bone. (4) Lodwick IB pattern - geographic, well-defined but no sclerotic margin. (5) No matrix - GCT is non-matrix producing (purely lytic). (6) Soap bubble appearance - may have internal trabeculation giving multiloculated appearance. (7) Common sites - distal radius, proximal tibia, distal femur, proximal humerus. The lack of sclerotic margin with subchondral extension in a young adult is classic for GCT.
KEY POINTS TO SCORE
GCT extends to subchondral bone (touches joint)
After skeletal maturity (20-40 years)
Lodwick IB: No sclerotic margin
Eccentric, purely lytic, no matrix
Soap bubble appearance
COMMON TRAPS
✗Diagnosing GCT in skeletally immature (would be chondroblastoma)
✗Missing the subchondral extension
✗Confusing with ABC (ABC more expansile)
VIVA SCENARIOStandard
EXAMINER
"A child presents after a minor fall with arm pain. X-ray shows a well-defined lytic lesion in the proximal humeral metaphysis with a fragment of bone lying in the dependent portion of the lesion."
EXCEPTIONAL ANSWER
This is the 'fallen fragment sign' (also called 'fallen leaf sign'), which is pathognomonic for unicameral bone cyst (UBC). The sign occurs because: (1) UBC contains serous fluid. (2) After pathological fracture, a cortical fragment or piece of the cyst wall falls to the dependent portion due to gravity. (3) This only occurs in fluid-filled cavities - solid lesions would not allow fragment migration. Features supporting UBC: Central metaphyseal location, well-defined margins (Lodwick IA), no matrix, and the classic proximal humerus location (most common site). UBCs are benign and often present with pathological fracture after minor trauma.
KEY POINTS TO SCORE
Fallen fragment sign pathognomonic for UBC
Fragment falls to dependent portion (fluid-filled)
Only occurs in fluid-filled cyst (not solid lesion)
Proximal humerus most common site
Often presents with pathological fracture
COMMON TRAPS
✗Missing the fallen fragment
✗Confusing with ABC (ABC more expansile, eccentric)
✗Not recognising the pathological fracture
Evidence Base
Lodwick Classification
4
Diagnostic Signs
3
3
Clinical Correlation
4
Key Evidence Points
- Lodwick grades: IA (well-defined sclerotic border) = benign, III (permeative) = aggressive
- Codman triangle: Always aggressive but not specific for malignancy
- Matrix patterns: Guide differential diagnosis (osteosarcoma = osteoid, chondrosarcoma = chondroid)
- Age and location: Essential for differential diagnosis
Tumour Signs Quick Reference
High-Yield Exam Summary
Lodwick Classification
- •IA: Geographic, sclerotic (benign)
- •IB: Geographic, defined (GCT, ABC)
- •IC: Geographic, ill-defined (low-grade)
- •II: Moth-eaten (myeloma, mets)
- •III: Permeative (Ewing's, round cell)
Periosteal Reactions
- •Codman triangle: Aggressive (not specific)
- •Sunburst: Osteosarcoma
- •Onion skin: Ewing's (also benign)
- •Hair-on-end: Ewing's, mets
Matrix Patterns
- •Rings/arcs: Cartilage tumour
- •Cloud-like: Osteoid (osteosarcoma)
- •Ground glass: Fibrous dysplasia
- •No matrix: Myeloma, mets, GCT
Pathognomonic Signs
- •Fallen fragment: UBC
- •Ground glass: Fibrous dysplasia
- •Nidus with sclerosis: Osteoid osteoma
- •Winking owl: Spinal metastasis