2.MSK - Bone Tumours

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)

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

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)

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

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

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

Answer 14

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

Question 15

Chordoma trivia

Answer 15

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