2. MSK p199-208 (Benign Lesions)

Question 1

Cystic bone lesions - DDx (8)

Answer 1

<30: EG (eosinophilic granuloma), ABC, NOF, Chondroblastoma, Solitary Bone Cysts
>40: Mets, Myeloma
Any age: Infection

Question 2

Epiphyseal lesions - DDx (5)

Answer 2

ABC (usually metaphyseal, but after growth plate closes it can extend into epiphysis)
Infection
Giant Cell
Chondroblastoma

Beware of epiphyseal equivalents (carpals, patella, greater trochanter and calcaneus)

Question 3

Malignant epiphyseal lesion (2)

Answer 3

Clear Cell Chondrosarcoma
- Slow growing, varied appearance (lytic, calcified, lobulated, ill defined)

Question 4

Metaphyseal lesions DDx (3)

Answer 4

Fastest growing area with best blood supply.
Increased predilection for mets and infection.
Most of the cystic bone lesions can occur here

Question 5

Diaphyseal lesions DDx

Answer 5

Most things can occur here, like the metaphysis, only less often

Question 6

Fibrous dysplasia features (5)

Answer 6

Skeletal developmental anomaly of osteoblasts (failure of normal maturation and differentiation).
Can occur at any age
- Monoostotic in 20s and 30s, polyostotic in <10.
Likes ribs and long bones.
Can occur in the pelvis, where it also affects ipsilateral femur (Shepherd Crook Deformity).
Multiple ones like skull and face (Lion-like faces)

Question 7

Fibrous dysplasia - imaging (4)

Answer 7

Very variable appearance, buzzword is groundglass.
Buzzword: long lesion in long bone
Textbook: Lytic lesion with hazy matrix.
No periosteal reaction or pain.

Question 8

McCune Albright vs Mazabraud syndrome (5)

Answer 8

Both Polyostotic Fibrous Dysplasia.
Girls vs Middle aged women
Cafe-au-lait spots vs Soft tissue myxomas.
Precocious puberty vs Increased risk of osseous malignant transformation.

Question 9

Adamantinoma (2)

Answer 9

Tibial lesion that resembles fibrous dysplasia (mixed lytic and sclerotic).
Potentially malignant.

Question 10

Enchondroma (5)

Answer 10

Tumour of medullary cavity composed of hyaline cartilage.
Lytic lesion with irregularly speckled calcification of chondroid matrix, classically described as arcs and rings.
Chondroid matrix is not found in the fingers or toes (high yield).
Enchondroma is most common cystic lesion of hands and feet.
No periostitis - like fibrous dysplasia

Question 11

Enchondroma vs Low grade chondrosarcoma

Answer 11

History of pain suggests chondrosarcoma

Question 12

Ollier’s syndrome vs Maffucci syndrome (2)

Answer 12

Only enchondromas
vs
Enchondromas and Haemangiomas, with malignant potential (20% turn into chondrosarcoma, other cancers such as GI and ovarian)

Question 13

Eosinophilic granuloma (7)

Answer 13

Seen usually in <30yo.
Can be solitary (usually) or multiple.
3 classic appearances
- Vertebra plana in a child
- Skull with lucent “beveled edge” lesions in a child
- “floating tooth” with lytic lesion in alveolar ridge
Varied appearance, can be lytic or blastic, with or without sclerotic border, with or without periosteal response.
Can have osseous sequestrum.

Question 14

DDx for Vertebral Plana (5)

Answer 14

MELT
Mets/myeloma
Eosinophilic Granuloma
Lymphoma
Trauma/TB

Question 15

DDx for Osseous Sequestrum (5)

Answer 15

Osteomyelitis
Lymphoma
Fibrosarcoma
EG
Osteoid Osteoma can mimic a sequestrum

Question 16

Giant cell tumour (5)

Answer 16

Criteria
- Physis MUST be closed
- Non-sclerotic border
- Abuts the articular surface
Considered “quasi-malignant” because they can be locally invasice and 5% have pulmonary mets.
These are curable and should be resected with wide margins

Question 17

Giant cell tumour - trivia (5)

Answer 17

Most common in the knee - abutting articular surface
Most common in age 20-30 (physis must be closed)
Associated with ABCs
Quasi-malignant - 5% have lung mets
Fluid levels on MRI

Question 18

Non-ossifying fibroma (6)

Answer 18

Common, seen in children
Will spontaneously regress (becoming more sclerotic before disappearing).
Rare in children not yet walking.
Tend to occur around the knee
Classically “eccentric with thin, sclerotic border” (GCTs don’t have sclerotic border).
If <2cm, called fibrous cortical defects (Fibroxanthoma is term for both)

Question 19

Osteoid osteoma (5)

Answer 19

Buzzwords
- Pain at night, relieved by aspirin
- Large amount of oedema for size of lesion
Seen in meta/diaphysis of long bones and posterior elements of spine, most commonly lumbar spine.
Associated with painful scoliosis with convexity pointed away from lesion.
Can be treated with percutaneous radiofrequency ablation (as long as not within 1cm of nerve or other vital structure, usually avoided in hands, spine and pregnant patients)

Question 20

Associations of osteoid osteoma (4)

Answer 20

Painful scoliosis
Growth deformity - increased length and girth of long bones
Synovitis: can be intra-articular, leading to early arthritis
Arthritis - due to primary synovitis or secondary from altered joint mechanics

Question 21

Osteoblastoma (3)

Answer 21

Osteoid osteoma >2cm
Seen in <30YO
Usually in posterior elements or long bones (35%), usually diaphyseal (75%)

Question 22

Metastatic disease (4)

Answer 22

Differential for anyone over 40 with lytic lesions.
Renal cancer mets are ALWAYS lytic.
Classic blastic lesions - prostate, carcinoid, medulloblastoma
Classic lytic lesions - renal, thryoid

Question 23

Multiple myeloma - features (3)

Answer 23

Plasma cell proliferation increases surounding osteolytic activity.
Usually older patients (40s-80s)
Plasmacytomas can precede clinical or haematologic evidence by 3 years

Question 24

Multiple myeloma - imaging (5)

Answer 24

Usually discrete margins, can be solitary or multiple.
Vertbral body destruction with sparing of posterior elements is classic.
Bone scan often negative.
Skeletal survey is better, MRI is most sensitive.
MM can manifest as diffuse osteopenia

Question 25

Plasmacytoma (4)

Answer 25

Discrete, solitary mass of neoplastic monoclonal plasma cells in bone or soft tissue.
Associated with latent systemic disease in most cses.
Can be considered singular counterpart of multiple myeloma.
Geographic lytic area, sometimes with expansile remodelling
Mini Brain Appearance - plasmacytoma in vertebral body

Question 26

POEMS (7)

Answer 26

Myeloma with sclerotic mets
Rare medical syndrome with plasma cell proliferation (myeloma) with neuropathy and organomegaly
- Polyneuropathy
- Organomegaly
- Endocrinopathy
- Monoclonal Gammopathy
- Skin changes

Question 27

Aneurysmal Bone Cyst (6)

Answer 27

Aneurysmal lesions of bone with thin walled, blood filled spaces (fluid-fluid level on MRI).
Usually <30YO.
May develop them following trauma.
Location: Tibia > vertebrae > femur > humerus
Primary or secondary, associated with another tumour (classicallyl GCT)
Commonly associated with other benign lesions

Question 28

Lucent lesion in posterior elements - DDx (3)

Answer 28

Osteoblastoma
ABC
TB

Question 29

Solitary (Unicameral) bone cyst (6)

Answer 29

Usually <30
More common in tubular bones (usually humerus or femur)
“Always located centrally”
Imaging
- 1) Fracture through it in the humerus w/fallen fragment sign
- 2) Lucent lesion in the calcaneus (probably w/fallen fragment sign)
Fallen fragment sign: Bone fragment in the dependent portion of lucent bone lesion is pathognomonic of solitary bone cyst.

Question 30

Brown tumour (4)

Answer 30

Associated with hyperparathyroidism.
Brown tumour represents localised accumulation of giant cells and fibrous tissues.
Lytic or sclerotic lesions with other findings of hyperparathyroidism (subperiosteal bone resorption, classically on side of finger, edge of clavicle or under a rib)
They resorb and can become totally sclerotic/healed when hyperparathyroid is treated.

Question 31

Chondroblastoma (4)

Answer 31

Seen in kids
1) Epiphysis of tibia on teenager or 2) in an epiphyseal equivalent.
Epiphyseal equivalents:
- Patella, Calcaneus, Carpal bones
- Apophyses (Greater and lesser trochanter, tuberosities, etc)

Question 32

Chondroblastoma - features (8)

Answer 32

Thin sclerotic rim.
Extension across physeal plate
Periostitis
Location: Femur > humerus > tibia.
May show marrow oedema and soft tissue oedema on MRI.
One of few bony lesions often NOT T2 bright.
Tend to reoccur afte rresection.
Chondroblastomas of the hip tend to favor the GT more than femoral epiphysis.

Question 33

Chondromyxoid fibroma (4)

Answer 33

Least common benign cartilage lesion.
Usually <30yo.
Osteolytic, elongated in shape, eccentrically located, metaphyseal lesion with cortical expansion and bit like confugiration.
Sort of looks like NOF

Question 34

Greater trochanter - DDX (3)

Answer 34

It’s an epiphyseal equivalent and the chondroblastomas prefer it to the femoral epiphysis.
ABC, Infection and GCT happen here too
Avulsions of the gluteus (minimus and medius)

Question 35

Lesser trochanter - DDx

Answer 35

Avulsion fracture without significant clinical Hx should make you think of pathologic fracture

Question 36

Intertrichanteric region DDx (3)

Answer 36

Lipoma,
solitary bone cyst and
monoostotic fibrous dyslplasia

Question 37

Calcaneal lesions - DDx (8)

Answer 37

Solitary bone cyst
- Sharp edges, thick sclerotic edge with multiloculated appearance is helpful.
- Fallen fragment will be more in the bottom if shown (but fractures of the calcaneus are less common)
Pseudocyst
- Variation in normal trabecular pattern, creates a central triangular radiolucent area
- Persistence of thin trabeculae and visible nutrient foramen, along with classic location, are helpful signs of this
Interosseous lipoma
- Fat density on CT or MRI
- Central fragment, stuck in the middle of the fat
- Calcification & fat necrosis occurs about 50% in the real world
Epiphyseal equivalent
- therefore ABC, infection, GCT and Chondroblastoma can occur here, tend to be more posterior calcaneus
Geode can mimim cystic lesion in older people with arthritis

Question 38

No periostitis or pain - DDx (4)

Answer 38

Fibrous dysplasia
Enchondroma
NF
Solitary Bone Cyst (unless fractured)

Question 39

Multiple lesions DDx (5)

Answer 39

Fibrous dysplasia
EG
Enchondroma
Mets/myeloma
Hyperparathyroidism

Question 40

Liposclerosing myxofibroma (3)

Answer 40

Characteristic location: Intertrochanteric region of femur
Geographic lytic lesion with sclerotic margin
10% undergo malignant degeneration so needs following

Question 41

Osteochondroma (5)

Answer 41

Most common benign tumour.
Can be radiation induced, making them the only benign skeletal tumour associated with radiation.
Small risk of malignant transformation (cartilage cap >1.5cm is concerning)
Point away from joint
Bone marrow flows freely into the lesion

Question 42

Multiple hereditary exostosis (2)

Answer 42

AD, multiple osteochondromas.
Increased risk of malignant transformation.

Question 43

Trevor disease (Dysplasia Epiphysealis Hemimelica (DEH)) (3)

Answer 43

Osteochondromas develop in epiphyses causing significant joint deformity (commonest in ankel and knee).
Can see in young children.
Osteochondroma looks like irregular mass.
Tend to be treated with surgical excision.

Question 44

Supracondylar spur (4)

Answer 44

aka avian spur.
Normal variant.
Osseous process, usually does nothing but can compress the median nerve if the ligament of Struthers smashes it.
Points towards joint (unlike osteochondroma)

Question 45

Periosteal chondroma (3)

Answer 45

aka Juxta-cortical chondroma
Lesion in finger of child
Rare, of cartilaginous origin,
Saucerization of the adjacent cortex with sclerotic periosteal reaction can be seen.

Question 46

Osteofibrous dysplasia (3)

Answer 46

Benign lesion in tibia or fibula in children.
looks like NOF but centered in the anterior tibia
Associated anterior tibial bowing.
Can occur with adamantinoma, 2 cannot be differentiated with imaging