経過観察中に著明な増大を認めて切除された脱分化を伴う後腹膜脂肪肉腫の1例

Dedifferentiated retroperitoneal liposarcoma showing a marked enlargement which was resected after follow-up：a case report

後腹膜脂肪肉腫は後腹膜悪性腫瘍の約51～62％を占め，解剖学的に症状が出現しにくいため巨大化して腹部腫瘤や腹部膨満感などの出現を契機に発見されることが多い。一方で，初発時からの自然経過が画像的に捉えられる症例は貴重とも言える。今回我々は腎周囲の非特異的脂肪織濃度上昇の増強として初発し，15カ月の経過中に腫瘤の発生と著明な増大を認めたため手術され，脱分化を伴った後腹膜高分化脂肪肉腫と診断された1例を経験したので，若干の文献的考察を加えて報告する。

A 79-year-old man underwent abdominal computed tomography（CT）as part of his periodic medical examination, and diffuse soft tissue attenuations were revealed in the right perirenal space. After 9 months, a cystic tumor developed in that same space. The tumor showed a marked enlargement, and a nodular lesion appeared 6 months later. The main tumor showed a mucinous cystic signal pattern, and the nodular lesion showed strong diffusion restriction on magnetic resonance imaging（MRI）. The lesions were then resected and were histologically assessed as comprising dedifferentiated liposarcoma together with well-differentiated liposarcoma. Herein, we report a case of dedifferentiated retroperitoneal liposarcoma, which was found as a cystic tumor and revealed a marked enlargement on assessment.