Age / Sex : 15 / F

Chief complaint : Right upper arm pain and swelling (3 weeks ago)

What is your impression?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Yoo Hye Jin, Seoul National University Hospital

Discussion

Answer:  

PERIOSTEAL OSTEOSARCOMA  

Findings:

X-ray: A broad-based surface soft-tissue mass in the diaphysis of the right midshaft of humerus involving the lateral cortex with perpendicular or sunburst pattern periosteal reaction.

MRI: Periosteal soft tissue mass with internal calcification in the diaphysis of the right midshaft of humerus involving the lateral cortex.

- appears hyperintense on T2 sequence, which represents its chondroid matrix.

- with periosteal hypointense portion on both T1 and T2 sequences, suggesting periosteal bone formation

- with heterogeneous contrast enhancement.

- no cortical or intramedullary bone involvement.

Differential Diagnosis:

Central osteosarcoma, Parosteal osteosarcoma

Discussion:

It is the second most common type of surface osteosarcoma after parosteal osteosarcoma and accounts for 1.5% of all osteosarcoma cases. It affects a slightly older age group (10-20 years).

Periosteal osteosarcoma arises from the inner layer of periosteum (parosteal osteosarcoma arises from outer layer) and contain large amount of cartilaginous matrix. Histologic grade of this tumor is higher than parosteal osteosarcoma and lower than conventional osteosarcomas, so it is considered as an intermediate grade osteosarcoma (grade 2). It predominantly contains chondroid matrix. It usually arises from cortex, being attached to underlying cortex at origin, but intramedullary extension is rare.

A central osteosarcoma is a central destructive lesion with varying amounts of osteoid matrix, is radiographically discernable. The tumor is aggressive with poorly defined matrix and damaged cortex. In parosteal osteosarcoma, a radiolucent zone between tumor and the bone of origin indicates a void between tumor mass, outgrowing its pedicle and cortex of the normal bone. The medullary cavity is violated and daughter mass is frequently observed. There is a mushrooming mass attached with a thick pedicle, which circumvents the shaft of origin and often invades the medullary cavity.

A periosteal osteosarcoma is of intermediate grade with prognosis being better than conventional osteosarcoma, but not as good as parosteal osteosarcoma (which is usually low grade).

References:

Radiology 2004; 233 (1): 129-038. Imaging of Periosteal Osteosarcoma: Radiologic-Pathologic Comparison

Int J Clin Exp Med. 2015; 8(1): 37–44. Periosteal osteosarcoma: a review of clinical evidence