軟部腫瘤―骨化性筋炎と肉腫

Diagnostic imaging of myositis ossificans and calcified or ossified sarcoma

軟部組織病変では，しばしば石灰化や骨化を有する場合がある。腫瘍壊死や脂肪壊死に伴う骨化・石灰化は種々の悪性・良性腫瘍で認められる非特異的所見で，必ずしも診断に有用とはいえない^1）。一方，特徴的な骨化・石灰化のパターンが診断確定の重要なポイントとなる病変もあり，その代表が骨化性筋炎である。本稿では，骨化性筋炎を中心に，骨化・石灰化が診断の決め手となる軟部腫瘍について説明する。

Soft tissue lesions often contain bone or cartilage matrix. The identification of ossification or calcification in a soft tissue lesion is important because it can narrow the differential diagnosis or be suggestive of a certain diagnosis. Myositis ossificans is a self-limiting, reactive, bone-forming process of soft tissue in patients with or without a history of trauma. On radiographs and CT, mature stage of myositis ossificans typically present as a round calcified lesion with a radiolucent center. However, in earlier stages, the peripheral calcification may not be well visualized, leading to misdiagnosis. MR findings of myositis ossificans are often nonspecific, because calcification or ossification is not reliably identified. This article focuses on myositis ossificans and describe soft tissue lesions in which presence of ossification or calcification can be a key for the diagnosis.