2. MSK p194-198 (Aggressive Lesions)

Question 1

Commonest primary osseous malignancies (3)

Answer 1

1) Myeloma/plasmacytoma (27%)
2) Osteosarcoma (20%)
3) Chondrosarcoma (20%)

Question 2

Osteosarcoma - Subtypes

Answer 2

Conventional intramedullary (85%)
Paraosteal (4%)
Periosteal (1%)
Telangectatic (rare)

Question 3

Conventional Intramedullary Osteosarcoma (general info)

Answer 3

Higher grade than surface subtypes
Typically younger pt (10-20)
Typically femur (40%) and proximal tibia (15%)

Question 4

Periosteal reactions (buzzwords)

Answer 4

Sunburst - Agressive periosteal reaction, looks like sunburst
Codman triangle - New periosteum doesn’t have time to completely ossify, so only raised edge ossifies
Lamellated (onion skin) - multiple layers of parallel periosteum

Question 5

High yield trivia (osteosarcoma)

Answer 5

Osteosarcoma met to lung is classic cause of occult pneumothorax
Reverse zoning - denser matrix in centre, less dense periphery

Question 6

Risk factors for pathologic fractures (3)

Answer 6

1 - Lytic lesions
2 - Lesions >3cm in size
3 - Lesions involving >50% of cortex

Question 7

Parosteal osteosarcoma (general) (5)

Answer 7

Low grade, bulky, parosteal bone formation.
BIG tumours.
Early adult/middle age.
Commonly posterior distal femur. 90% metaphysis.
String sign: radiolucent line separating bulky tumour from cortex.

Question 8

Periosteal osteosarcoma (5)

Answer 8

Worse prognosis than parosteal, better than conventional intramedullary.
15-25YO.
More commonly diaphyseal.
Classically medial distal femur.
No marrow extension unlike parosteal (50%).

Question 9

Telangectatic Osteosarcoma (general) (4)

Answer 9

15% have narrow zone of transition.
Fluid-fluid level on MRI is classic.
T1 bright (methaemoglobin).
Tumour nodularity and enhancement differentiates from CGT and ABC

Question 10

Fluid-fluid levels DDx (3)

Answer 10

Telangectatic Osteosarcoma
Aneurysmal Bone Cyst
Giant Cell Tumour

Question 11

Chondrosarcoma (4)

Answer 11

Usually older adults (M>F)
Flat bones, proximal tubular bones, limb girdles.
Central (intramedullary) or peripheral (end of osteochondroma)
Usually low grade

Question 12

Chondroblastoma in adult

Answer 12

Clear cell chondrosarcoma

Question 13

Ewings sarcoma (3)

Answer 13

Permeative lesion in the diaphysis of child
Usually mets bone to bone
Mimic osteosarcoma due to marked sclerosis (occurs in bone only, not soft tissue like osteosarcoma)

Question 14

Chordoma (3)

Answer 14

Age 30-60, younger in clivus, older in sacrum
Very T2 bright
Sacrum > Clivus > Vertebral body

Question 15

Chordoma trivia (3)

Answer 15

Commonest primary malignancy of spine or sacrum
Most common spinal location is C2
Almost always midline

Question 16

Fibrosarcoma (4)

Answer 16

Can be primary or secondary (Pagets, infarct etc).
Lytic malignant tumours that DONT produce osteoid or chondroid matric.
Almost always lytic, may be permeative or moth eaten
NOT T2 bright (most tumours are)

Question 17

MFH (5)

Answer 17

Malignant Fibrous Histiocytoma (Now called Pleomorphic Undifferentiated Sarcoma (PUS)).
More common than fibrosarcomas, most common soft tissue sarcoma in adults.
Look radiologically similar to fibrosarcoma.
Bone infarcts can turn into MFH (Buzzword: Sarcomatous transformation of infarct)

Question 18

Synovial sarcoma - features (3)

Answer 18

Commonest in lower extremities of patients aged 20-40.
Close to (but not in) joint.
10% get secondary invasion into the joint (for multiple choice, they “never involve joint)

Question 19

Synovial sarcoma - imaging (3)

Answer 19

Triple sign
- High, medium and low signal in the same mass on T2 (usually knee)
Bowl of grapes
- Bunch of fluid-fluid levels in a mass (probably knee)
Plain film
- Soft tissue component with calcifications, least likely way to show it.

Question 20

Synovial sarcoma - trivia (6)

Answer 20

Most sarcomas don’t attach bones, these can.
Most present as painless mass, these hurt.
Soft tissue calcifications + bone erosions are highly suggestive.
Show growing & small, often lead people to call them benign.
90% have translocation of X-18.
Most common malignancy in teens/young adults of foot, ankle and lower extremity

Question 21

Ball like tumour in extremity of young adult

Answer 21

Synovial sarcoma

Question 22

Liposarcoma (4)

Answer 22

2nd commonest soft tissue sarcoma.
Common in middle aged, commonly in retroperitoneum (can also happen in extremities).
Most common type is well differentiated (least aggressive).
Fatty mass in the retroperitoneum = Liposarcoma

Question 23

Liposarcoma vs lipoma (3)

Answer 23

Imhomogenous attenuation - soft tissues masses in the fat
Infiltration of adjacent structures
Deep and big

Question 24

Myxoid liposarcoma (3)

Answer 24

Commonest liposarcoma in <20yo.
Can be T2 bright but T1 dark, not a cyst.
Needs gadolinium imaging

Question 25

Treeatment of agressive lesions (4)

Answer 25

Osteosarcoma - Chemo (to kill micro mets) then wide excision.
Ewings: Chemi and Radiation, then wide excision.
Chondrosarcoma: Usually just wide excision (low grade, main concern is local recurrence)
Giant Cell Tumour: Usually requires arthroplasty as it extends to articular surface.

Question 26

Myositis ossificans (3)

Answer 26

Circumferencial calcifications with lucent centre.
Can look scare on MRI if imaged early due to oedema and avid enhnacement.
Benign, don’t biopsy

Question 27

Avulsion injury (2)

Answer 27

Typically near pelvis, can have aggressive periosteal reaction.
Benign, don’t biopsy.

Question 28

Cortical desmoid (3)

Answer 28

Classically on posterior medial epicondyle of distal femur.
Can be hot on bone scan.
Benign, don’t biopsy.

Question 29

Synovial Herniation Pit (4)

Answer 29

Aka pitt’s pit.
Characteristic location in femoral neck.
Lytic appearing lesion.
Benign, don’t biopsy

Question 30

Bone biopsy (5)

Answer 30

D/W ortho to avoid contaminating parts not involved by tumour.
Pelvis: Avoid crossing gluteal muscles (may be needed for reconstruction).
Knee: Avoid joint space via crossing suprapatellar bursa or other communicating bursae.
Avoid crossing Quads tendon unless involved.
Shoulder: Avoid posterior 2/3 (axillary nerve courses post to anterior, therefore posterior resection will denervate antererior third)