MSK tumors

Question 1

Parosteal vs periosteal osteosarc:
Location (epi, meta, dia)?
Forms mature bone?
Prognosis?

Answer 1

Parosteal: metaphyseal (posterior distal femur is classic); mature bone centrally with surrounding osteoid matrix; slow growing, low grade, better prognosis

Periosteal: diaphyseal; less mature bone; worse than parosteal, better than conventional OS

Question 2

Buzzword
String sign: radiolucent line separating tumor from cortex
What tumor?

Answer 2

Parosteal osteosarcoma

Question 3

Osseous tumor with fluid-fluid levels…

ddx?

Answer 3

Telangiectatic osteosarcoma
Aneurysmal bone cyst
Giant cell tumor

Question 4

Enchondroma vs chondrosaroma

Factors favoring chondrosarcoma?

Answer 4

• Cortical destruction
• Scalloping >2/3 cortex
• > 5cm size
• “Changing matrix”

Question 5

Ewings sarcoma vs osteosarcoma

Which affects surrounding soft tissues and which is restricted to bone?

Answer 5

Ewings = bone only

Osteo = bone and soft tissues

Question 6

Where do you find chordomas? (3 places)

Answer 6

Sacrum > clivus > vertebral bodies (C2)

Question 7

What lesions like the Epiphysis? (mnemonic hint: epiphysis = “evil”)

Answer 7

AIG the “evil” Company (AIGC):

• Aneurysmal bone cysts (ABC) (usually metaphyseal)
• Infection
• Giant cell
• Chondroblastoma (child) or Clear Cell Chondrosarcoma (adult)

Question 8

Most common lucent lesions in adult (>40)?

Answer 8

Mets
Myeloma
INFECTION

Question 9

Where would you find an adamantinoma? (2 places)

Answer 9

• Mandible

- Tibial shaft

Question 10

Where would you find a solitary bone cyst? (4 places)

Answer 10

• Proximal humerus
• Proximal femur
• Iliac bone
• Calcaneus

Question 11

Tumor of the epiphysis in a young patient?

Answer 11

Infection

Chondroblastoma

Question 12

Malignant epiphyseal tumor?

Answer 12

Clear cell chondrosarcoma

Question 13

Oval lytic lesion centered WITHIN dense cortical bone, +/- central sclerotic nidus?

Answer 13

Osteoid osteoma
Benign
Painful

Question 14

3 common locations for osteoid osteoma

Answer 14

Femur
Tibia
Spine

Question 15

Punched-out lytic calvarial lesions, beveled edges, kid

Answer 15

Langerhans cell histiocytosis

Question 16

TRIAD:

1. Diabetes insipidus
2. Proptosis/exophthalmos
3. Lytic bone lesions

Answer 16

Hand-Schuller-Christian

• Multifocal histiocytic disorder (like LCH)

Question 17

• Permeative lytic lesion
• Diaphysis or metadiaphysis of long bones
• Lamellated periosteal reaction (“onion-skin”)

Answer 17

Ewing sarcoma

Question 18

Most common sarcoma in children/adolescents?

Answer 18

Osteosarcoma

…then Ewing sarcoma

Question 19

Differentiate osteosarcoma from Ewing sarcoma

• Location?
• Periosteal reaction?
• Matrix?

Answer 19

• Location? OS = metaphysis; ES = metadiaphysis… not that helpful
• Both permeative/aggressive
• OS = INTERRUPTED periosteal reaction; ES = ONION SKIN
• OS = OSTEOID MATRIX; ES = NO matrix

Question 20

How common is Ewing sarcoma in African Americans?

Answer 20

NOT… not at all.

9x more common in caucasians. If stem says AA pt, consider anything else.

Question 21

Non-ossifying fibroma:

• Location (epi/meta/dia)?
• Most common bones?
• Appearance?

Answer 21

• Metaphysis, can grow to the metadiaphysis
• Distal femur, tibia most commonly
• Cortically-based, bubbly lytic appearance with thin sclerotic margins
• Will eventually heal/involute, becoming sclerotic, then completely resolve

Question 22

1. NOF aka?

2. Tiny NOF (<3cm) = ____?

Answer 22

1. Fibroxanthoma

2. Tiny non-ossifying fibroma (<3cm) = benign fibrous cortical defect (BFCD)