非典型的な画像所見を呈した骨膜性骨肉腫の1例

A case of the periosteal osteosarcoma presenting atypical imaging findings

骨膜性骨肉腫は骨膜骨形成層を発生母地とする中間悪性度の表在性骨肉腫の1つであり，骨肉腫の中でも発生率が2％未満とまれである。画像所見は単純X線やCTで骨膜反応を伴う骨外腫瘤が典型的であるが，骨膜反応を認めない非典型的な画像所見を呈した骨膜性骨肉腫の症例を経験した。他の表在性骨肉腫と比較しながら，画像所見を中心に若干の文献的考察を加え報告する。

A 25-year-old woman presented with swelling of her right lower leg. There was a right tibial mass with calcification but periosteal new bone formation wasn’t seen on plain X-ray images. CT and MRI showed that the calcified mass and the center of it was continuous with the bone cortex, but its margin was separated from the bone cortex. The mass was resected and the final diagnosis was periosteal osteosarcoma, but it was difficult to distinguish between periosteal osteosarcoma and parosteal osteosarcoma by the imaging findings.