Age / Sex : 16 / M

Periosteal osteosarcoma

Discussion

Findings:

Lateral radiograph of femur shows perpendicular periosteal reaction and Codman’s triangle in anterior aspect of the distal diaphysis. MR images show a well defined, broad-based, juxtacortical soft tissue mass and bone marrow edema. On axial MR images, soft tissue mass surrounds approximately two-thirds of the cortical circumference. Rays of low signal intensity on sagittal and axial T2WI and Gd enhanced T1WI correspond to perpendicular periosteal reaction.

Differential Diagnosis:

Periosteal osteosarcoma

High-grade surface osteosarcoma

Parosteal osteosarcoma

Diagnosis:  

Periosteal osteosarcoma

Discussion:

Periosteal osteosarcomas often show a distinctive imaging appearance—that of a diaphyseal lesion involving the femur or tibia(>85%) with cortical thickening that is extrinsically eroded (scalloped) by a broad-based soft-tissue mass attached to the cortex. Periosteal reaction (perpendicular to the long axis of the affected bone) extends into the soft-tissue mass, and additional areas of mineralization are frequently seen on radiographs. Rarely Codman’s triangle is seen. CT and MR imaging also show these features and reveal the extent of the soft-tissue mass. Periosteal osteosarcoma surrounds about 50% (30~90%) of circumference of the cortex. CT and MR imaging also reflect the largely chondroid tissue seen pathologically, which shows low attenuation at CT and high signal intensity at T2-weighted MR imaging. MR imaging commonly reveals foci of marrow edema in the region of the tumor. However, medullary invasion is rare and should only be suggested when the marrow replacement is in continuity with the surface soft-tissue component. Marrow signal abnormality that is not contiguous with the remainder of the tumor represents reactive change, and distinction of this abnormality from medullary invasion is important for determining the extent of tumor resection. Most patients with periosteal osteosarcoma are 10-20 years of age, similar to conventional osteosarcoma.       

Juxtacortical or surface osteosarcoma refers to osteosarcoma originating from the surface of bone. It is primarily associated with the periosteum, with variable medullary canal involvement. Juxtacortical or surface osteosarcoma is classified into three main subtypes—parosteal, periosteal, and high-grade surface osteosarcoma. Periosteal osteosarcoma is the 2^nd most common type(1.5% of all osteosarcoma) after parosteal osteosarcoma(5% of all osteosarcoma).

The differential diagnosis of periosteal osteosarcoma includes parosteal osteosarcoma, high-grade surface osteosarcoma, periosteal (or juxtacortical) chondrosarcoma, and periosteal Ewing sarcoma,. Parosteal osteosarcoma characteristically affects older patients (in the late 3rd or 4th decade of life), involves the metaphysis (particularly the posterior part of the distal portion of the femur) without perpendicular periosteal reaction, and is initially attached to the bone by a narrow stalk. High-grade surface osteosarcoma is often the most difficult lesion to distinguish from periosteal osteosarcoma because both are usually diaphyseal and show a perpendicular periosteal reaction. Compared with periosteal osteosarcoma, high-grade osteosarcomas usually surround a much higher percentage of the bone circumference, are more likely to invade the medullary canal, and do not consist of a high-water-content soft-tissue mass that shows low attenuation at CT, very high signal intensity on T2-weighted MR images, and/or peripheral and septal enhancement resulting from the presence of a cartilaginous component. Periosteal  chondrosarcoma (in 2nd to 4th decade of life) most commonly occurs in the metaphysis and often shows extensive osteoid and chondroid mineralization. In addition, although cortical scalloping and thickening are frequent, perpendicular periosteal reaction is usually not apparent. Ewing sarcoma is only rarely periosteal (3% of cases) without medullary involvement but can closely simulate periosteal osteosarcoma in terms of patient demographics, lesion location, and radiologic appearance. However, mineralization within the soft-tissue component, perpendicular periosteal reaction (before chemotherapy), and low attenuation in the soft-tissue component at CT and very high signal intensity of the component on T2-weighted MR images are not typical features of periosteal Ewing sarcoma.

References:

1. Yarmish G, Klein MJ, Landa J, Lefkowitz RA, Hwang S. Imaging characteristics of primary osteosarcoma: nonconventional subtypes. Radiographics. 2010; 30:1653-1672.


2. Murphy MD, Jelinek JS, Temple HT,  Flemming DJ, Gannon FH. Imaging of periosteal osteosarcoma: Radiologic-pathologic comparison. Radiology 2004; 233:129-138


3. Chaabane S, Bouaziz MC, Drissi C, Abid L, Ladeb MF. Periosteal chondrosarcoma. AJR 2009; 192:W1-W6