Answer for BIR CoW 12 Nov 2023
Parosteal Osteosarcoma
Findings
An exophytic lesion with dense osteoid matrix is seen arising from the cortical surface of lateral aspect of proximal tibial metaphysis. A thin lucent line is seen separating the lesion from the adjacent cortex.
Discussion
Osteosarcoma is a malignant tumor of connective tissue that produces osteoid matrix. The current WHO classification of OS of bone includes eight categories: conventional, telangiectatic, small cell, low-grade central, secondary, parosteal, periosteal, and high-grade surface. Juxtacortical OS is now classified into three main subtypes— parosteal, periosteal, and high-grade surface. Parosteal OS is the most common type of juxtacortical OS. The tumor occurs in the metaphyses of long bones , and the posterior aspect of the distal femur is the most frequent site. The prognosis for parosteal OS is better than that for conventional OS. Anatomically, parosteal OS originates from the outer fibrous layer of the periosteum and is usually low grade. Imaging- Radiography - the classic appearance is a lobulated and exophytic mass with central dense ossification adjacent to the bone . A cleavage plane separating the tumor and adjacent normal cortex ,known as the string sign has been reported in 30% . This cleavage plane corresponds histologically to the periosteum interposed between the cortex and the tumor mass. Cortical thickening with a relative lack of aggressive periosteal reaction is often apparent, due to focal expansion of the inner portion of the tumor and fusion with the cortex.
Differential Diagnosis:
Osteochondroma
Periosteal osteosarcoma
Myositis ossificans
Periosteal chondroma
References:
Yarmish, G., Klein, M. J., Landa, J., Lefkowitz, R. A., & Hwang, S. (2010). Imaging Characteristics of Primary Osteosarcoma: Nonconventional Subtypes. RadioGraphics, 30(6), 1653–1672. doi:10.1148/rg.306105524.
Findings
An exophytic lesion with dense osteoid matrix is seen arising from the cortical surface of lateral aspect of proximal tibial metaphysis. A thin lucent line is seen separating the lesion from the adjacent cortex.
Discussion
Osteosarcoma is a malignant tumor of connective tissue that produces osteoid matrix. The current WHO classification of OS of bone includes eight categories: conventional, telangiectatic, small cell, low-grade central, secondary, parosteal, periosteal, and high-grade surface. Juxtacortical OS is now classified into three main subtypes— parosteal, periosteal, and high-grade surface. Parosteal OS is the most common type of juxtacortical OS. The tumor occurs in the metaphyses of long bones , and the posterior aspect of the distal femur is the most frequent site. The prognosis for parosteal OS is better than that for conventional OS. Anatomically, parosteal OS originates from the outer fibrous layer of the periosteum and is usually low grade. Imaging- Radiography - the classic appearance is a lobulated and exophytic mass with central dense ossification adjacent to the bone . A cleavage plane separating the tumor and adjacent normal cortex ,known as the string sign has been reported in 30% . This cleavage plane corresponds histologically to the periosteum interposed between the cortex and the tumor mass. Cortical thickening with a relative lack of aggressive periosteal reaction is often apparent, due to focal expansion of the inner portion of the tumor and fusion with the cortex.
Differential Diagnosis:
Osteochondroma
Periosteal osteosarcoma
Myositis ossificans
Periosteal chondroma
References:
Yarmish, G., Klein, M. J., Landa, J., Lefkowitz, R. A., & Hwang, S. (2010). Imaging Characteristics of Primary Osteosarcoma: Nonconventional Subtypes. RadioGraphics, 30(6), 1653–1672. doi:10.1148/rg.306105524.
Note:
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!