pure MSK

Question 1

Osteochondroma demographys

Answer 1

most common benign bone lesion
usually <20 year olds
can present with mass effect, #, malignant Tx
multiple - MHE

Question 2

osteochondroma features

Answer 2

exophytic pedunculated or sessile bone projection capped by cartilage
- cortical and medullary components
- grow away joint
- thickness of cap

DDX: bone spur (grows towards joint), periosteal lesion, BPOP/NORA (reactive lesion)

Question 3

osteochondroma complication

Answer 3

cosmetic deformity
#
vascular/neuro compromise
bursal formation
malignant transformation (<1% solitary osteochondromas, 2-5% for HME)

Question 4

sign of osteochondroma malignant Tx

Answer 4

continued growth after skeletal maturity
pain

Question 5

intramedullary chondroid lesion DDx

Answer 5

enchondroma vs low grade chondrosarc

Question 6

enchondroma features

Answer 6

benign hyaline cartilage producing tumor of medullary bone
child->adults, peak 10-30yo.
phalanges and long bones.
well defined, lucent defect
central > eccentic, may be expansile
variable chondroid matrix (not in phlanges)

Question 7

cartilage lesions on MR?

Answer 7

lobulated, high signal, enhancement accentuates lobules

Question 8

why should you not Bx an asymptomatic enchondroma?

Answer 8

because histologically it is the same as low grade chondrosarc!

Question 9

what features favor low grade chondrosarc over enchondroma?

Answer 9

• older age, male, PAIN
• cartilage lesion in FLAT and Epiphysis (clear cell CS)
• > 5-6cm in diameter
• endosteal scalloping >2/3 cortex or >2/3 length
• periosteal rxn, fracture, soft tissue mass

Question 10

cartilagenous bone lesions DDx

Answer 10

enchondroma
chondroblastoma
chondromyxoid fibroma
osteochondroma
chondrosarcoma

Question 11

chondromyxoid fibroma

Answer 11

extremely rare
metaphysis (upper tib, femur)
- lobulated, ovoid, eccentric. sclerotic rim 80%, often expansile. no periosteal rxn, uncommon to have calcified matrix

Question 12

chondroblastoma

Answer 12

young patients (10-20)
epiphysis or apophysis, long bone, eccentric beside physis.
- lytic, narrow TZ, cortex scalloping/thinning, expansile, metadiaphyseal periosteal rxn
- may breach cortex
- may have joint effusion

Question 13

enchondroma vs bone infarct

Answer 13

enchondroma: internal matrix, non-sclerotic borders, may have endosteal scalloping
BI: well defined sclerotic serpiginous border. no endosteal scalloping

Question 14

multiple enchondromas

Answer 14

Maffucci - ME + hemangioma
Ollier’s

Question 15

GCT features

Answer 15

‘benign’, locally aggressive neoplasm of osteoclast-like giant cells - 15-25% recurrence post rx. 1-6% lung ‘mets’
mature bones, 20-30yo MC,
epiphysis of long bones, sacrum, apophyses (MC neoplasm of patella)
- ABUTS ARTICULAR SURFACE, eccentric.
- Non sclerotic border
- expansile, destruction, soft tissue component

Question 16

ddx GCT

Answer 16

ABC (no soft tissue component)
chondroblastoma (OPEN physis, sclerotic margin, matrix)
myeloma/ mets
chondrosarc
telangiectatic OS

Question 17

fluid-fluid levels in GCT ?

Answer 17

GCT with secondary ABC !
- ABCs are usually much more expansile than GCT, and older patients

Question 18

GCT classic description?

Answer 18

eccentric, expansile, lytic lesion in the epiphysis extending to the articular surface without a scerotic rim, in a skeletally mature patient

Question 19

ABC features

Answer 19

benign expansile lucent lesion <30 yo.
primary or secondary (NOF, GCT, chondroblastoma, osteoblastoma)
- very expansile
- eccentric (SBC is central!)
- metaphysis/epiphysis/apophysis location, spine
- fluid-fluid levels

Question 20

fluid-fluid levels in a bone lesion

Answer 20

ABC, telangiectatic OS, SBC if #, GCT+ABC

Question 21

secondary ABCs develop in?

Answer 21

NOF, GCT, chondroblastoma, osteoblastoma

Question 22

sign of a secondary ABC?

Answer 22

expansile lesion with fluid-fluid levels in a soft tissue lesion

Question 23

lytic epiphyseal lesion/physis in peds DDx

Answer 23

chondroblastoma
osteomyelitis
GCT (but this is CLOSED growth plate)

Question 24

chondroblastoma features

Answer 24

epiphysis but if large, can extend into MP. Eccentric.
sharp margins. thin sclerotic im.
matrix in 25-40%
can have surrounding inflammation

Question 25

osteomyelitis epiphysis features

Answer 25

ill-defined irregular margins, if abscess, peripheral enhancement/central portion does NOT enhance

Question 26

chondroblastoma DDx

Answer 26

GCT (if closed growth plate, but not a lot of BM and soft tissue edema)
ABC
clear cell chondrosarc on XR (closed physis)

Question 27

benign bone lesions with lots of soft tissue edema?

Answer 27

osteoid osteoma
osteoblastoma
chondroblastoma

Question 28

osteoid osteoma definition

Answer 28

b enign bone tumor characterized by central nidus of osteoid, osteoblasts and variable amounts of fibrovascular stroma. nidus surrounded by dense, reactive bone

Question 29

osteoid osteoma features

Answer 29

10-11% of benign BTs
M>F, 10-25yo.
intensely vascular, ++BM and ST edema
metaphysis/diaphysis, femur neck/posterior elements
often intracortical.
lucent nidus, dense sclerotic surrounding bone –> hard to see on MR - CT better- oval/round areas of low density.
central nidus enhances strongly

Question 30

which is larger, NOF or FCD?

Answer 30

> 2cm length is FCD, >2cm NOF