Juxtacortical Osteosarcoma

Epidemiology

 

Uncommon

- 4% OS

 

Females more common 

- similar to GCT

 

NHx

 

Less aggressive locally

- less metastasis

- size / location & duration of symptoms don't correlate with outcome

 

Arise from cortex of bone / periosteum

- parosteal 

- periosteal

- high grade juxtacortical

 

Parosteal Osteosarcoma

 

Epidemiology

 

Comprise most of the 4%

Older (20-40)

Females

 

NHx

 

Lower grade

 

May dedifferentiate (late) into high grade lesion

 

Location

 

Arises from periosteal surface

- in the soft tissues adjacent to the periosteum 

 

Most common in posteromedial distal femur 

- popliteal Fossa

 

Also tibia & humerus

 

Slow indolent growth with eventual invasion of the underlying bone

 

Clinical

 

Painless block to knee flexion

 

X-ray

 

Parosteal Osteosarcoma XrayParosteal Osteosarcoma Xray Lateral

 

May look like osteochondroma

- large lobulated broad-based lesion

- mature bone arising from cortex

- underlying cortex may be thickened

- 25% invade periosteum

- lesion dense with bony pattern

 

"String Sign"

- wraps around bone with intervening periosteum

- gives well-defined radiolucent line

- thin radiolucent line between lesion & cortex

 

CT / DDx from Osteochondroma

 

1. Parosteal OS 

- attached to cortex growing into ST

- normal cortex intact

 

Parosteal Osteosarcoma CT0001Parosteal Osteosarcoma CT0002

 

2. Osteochondroma

- cortex of bone becomes cortex of osteochondroma

- there is modelling of cortex into the tumour

- medullary canal confluent with Exostosis

- posterior femur rare

 

DDx

 

NB Cortical tumours of posterior femur should be considered malignant

 

Osteochondroma

 

Myositis Ossificans

- more mature in periphery

- "like an agg"

- not attached to bone

 

Classic OS

 

Periosteal Chondroma

 

Osteoma

 

Subperiosteal Haematoma

 

MRI

 

Parosteal Osteosarcoma MRI0001Parosteal Osteosarcoma MRI0002

 

Pathology

 

Low grade

 

Regularly arranged bone

- background of spindle cells & fibrous tissue

- may have cartilage cap

- can encircle bone

 

Management

 

Wide Resection

 

Margins

- 7cm proximal & 5cm distally 

- femur: resect posterior capsule & condyles with lesion

 

Parosteal OS Resection0001Parosteal OS Resection0002

 

Prognosis

 

80% cure with surgery alone

 

Periosteal Osteosarcoma

 

Epidemiology

 

Rare +++

15-25

 

Location

 

Diaphysis of major long bones

- typically anterior proximal tibia

- humerus

 

Periosteal Osteosarcoma Anterior Tibia

 

NHx

 

"Peri is a rare bad boy"

- higher grade

 

Pathology

 

AKA High grade juxtacortical chondroblastic OS

- classically shows cartilage +++ 

- c.f. parosteal OS

 

X-ray

 

Punched out lesion

- calcified mass

- in a saucer shaped defect in the cortex

 

MRI

 

Periosteal Osteosarcoma MRI

 

Management

 

Wide resection with neoadjuvant & adjuvant chemotherapy

- DXRT stop local recurrence

 

Periosteal Osteosarcoma Wide Resection0001Periosteal Osteosarcoma Wide Resection0002