Parosteal Osteosarcoma

 

Parosteal 1Parosteal 2

 

Natural history

 

Low grade parosteal osteosarcoma

- less aggressive locally

- low incidence of metastasis

 

Epidemiology

 

Uncommon - 4% of osteosarcoma

 

Females more common

 

Natural History

 

Rajakulasingam et al Skeletal Radiol 2021

- 71 patients

- 43 femur, 14 tibia most common

- 60% low grade, 40% dedifferentiated high grade

- no metastasis seen at presentation on bone scan / CT chest / whole body MRI

- 10% (7 patients) with dedifferentiated tumor had lung metastasis later

- 6/7 had local recurrence

 

Location

 

Arises from periosteal surface of bone

 

Most common in posteromedial distal femur / popliteal fossa

 

Also tibia & humerus

 

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

 

"String Sign"

- wraps around bone with intervening periosteum

- well-defined radiolucent line between lesion & cortex

 

Parosteal OS tibia

 

parosteal tibia 1Parosteal tibia 2

 

CT

 

Can be used to differentiate from osteochondroma

 

1. Parosteal OS 

- attached to cortex growing into soft tissue

- normal cortex intact

 

Parosteal Osteosarcoma CT0001Parosteal Osteosarcoma CT0002

Parosteal osteosarcoma distal femur

 

Parosteal OS CT 1Parosteal OS CT 2

Parosteal Osteosarcoma distal femur

 

Parosteal tibia CTParosteal tibia CT

Parosteal Osteosarcoma proximal tibia

 

2. Osteochondroma

- cortex of bone becomes cortex of osteochondroma

- medullary canal confluent with osteochondroma

- posterior femur rare

 

Osteochondroma humerus

Osteochondroma humerus

 

Differential diagnosis

 

# Cortical tumors of posterior femur should be considered malignant #

 

Osteochondroma

 

Osteoid Osteoma

 

Osteoid osteoma

Osteoid Osteoma anterior tibia

 

Heterotopic ossification

- not attached to bone

 

Heterotopic ossification

Heterotopic ossification quadriceps following trauma

 

MRI

 

Parosteal Osteosarcoma MRI0002Parosteal OS MRI 2

Parosteal osteosarcoma posterior distal femur

 

Parosteal OS tibia MRI

Parosteal osteosarcoma anterior tibia

 

Parosteal tibia MRI 2Parosteal tibia MRI

Parosteal osteosarcoma posterior tibia

 

Pathology

 

Gross

 

Attached to cortex

Does not penetrate medullary cavity

 

Histology

 

Low grade

- irregular bony trabeculae and bland-appearing spindle cells within the fibrous stromal tissue

- atypical cells and atypical mitoses are not present

- may have cartilage cap

 

Can dedifferentiate with much poorer prognosis

 

Management

 

Wide Resection

 

A. Hemicortical resection and posterior hemicortical allograft reconstruction

- no chemotherapy if low grade

 

Parosteal OS 4Parosteal OS 6Parosteal OS 5

 

Parosteal OS tibia wide resection 1Parosteal OS tibia wide resection 2

 

B. Dedifferentiated parosteal Osteosarcoma

 

Parosteal tibia resect 1Parosteal tibia resection

 

Prognosis

 

Factors

- dedifferentiation

- local recurrence / importance of wide resection

- no obvious advantage with chemotherapy

 

Survival

- 96% 20 year survival for low grade

 

Results

 

Prognosis

 

Ruengwanichayakun et al Hum Pathol

- 147 low grade parosteal OA

- 5 year survival 96%

- 10 year survival 96%

- dedifferentiated parosteal OS 5 year survival 65%

 

Han et al J Surg Oncol 2008

- 21 patients with 9 year follow up

- 95% survival

- two patients with tumor positive surgical margins on histology

- both had local recurrence, one with recurrence and metastasis

 

Laitinen et al Bone Joint J 2015

- 80 patients with parosteal osteosarcoma

- local recurrence poor prognosis for survival

- importance of wide surgical margins

 

Jamshidi et al Orthop Traumatol Surg Res 2022

- 30 patients with low grade parosteal OS

- 14 cases tumor adhered to neurovascular bundle, 16 without

- all patients treated with resection / limb salvage

- 2 local recurrences in each group

 

Functional outcome

 

Deijkers et al JBJS Br 2002

- hemicortical resection and hemicortical allograft reconstruction

- 22 cases (6 parosteal, 6 peripheral chondrosarcoma, 10 adamantinoma)

- all allografts incorporated

- 6/22 (27%) patients had a fracture of the remaining host hemicortex

- good excellent functional outcome in 21/22 patients

 

Bus et al JBJS Am 2015

- hemicortical resection and hemicortical allograft reconstruction

- 111 cases (18 parosteal, 37 adamantinoma)

- 18% host bone fracture

- 7% nonunion

- 7% infection

- 3% allograft fracture