Age / Sex : 23 / F

Chief complaint: Slow growing upper arm mass

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한개만 보내주시기 바라오며, 복수의 답안을 보내주시는 분은 정답이 포함되어 있더라도 부득이 semi-correct answer로 처리토록 하겠습니다.)

Courtesy: 이성문 (Lee, Sung Moon), 계명의대 동산의료원(Dongsan Hospital, Keimyung University)

Parosteal osteosarcoma

Discussion

Findings:

1.     Lobulated and exophytic mass with central dense ossification adjacent to bone

2.     Radiolucent cleavage plane between tumor and adjacent cortex (string sign)

3.     Unmineralized peripheral soft tissue mass

4.     Lack of aggressive periosteal reaction

Differential Diagnosis:

1.     Periosteal (Juxtacortical) chondroma/chondrosarcoma
- chondroid mineralization
- cortical saucerization because it originates from deep layer of periosteum
 (inner germinative layer)
- periosteal reaction

2.     Periosteal osteosarcoma
- originated from inner germinative layer of periosteum
- periosteal reaction
- no string sign
- relatively rare intramedullary extension

Diagnosis:  

Parosteal osteosarcoma

Discussion:

1.     Juxtacortical osteosarcoma
1) parosteal OSA
2) periosteal OSA
3) high-grade surface OSA

2.     Parosteal OSA
1) 5% of all osteosarcoma
2) 2^nd to 4^th decades of life
3) Originated from outer fibrous layer of the periosteum
4) Central dense ossification, and peripheral nonmineralized soft tissue mass
5) Cleavage between tumor and adjacent cortex (String sign) – interposed periosteum
6) Lack of aggressive periosteal reaction (due to outer layer origin)
7) Frequent intramedullary invasion in both low-grade and high-grade lesions

References:

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