多骨性線維性骨異形成症に続発した肋骨骨肉腫

Osteosarcoma Secondary to Polyostotoic Fibrous Dysplasia of the Ribs

線維性骨異形成症はしばしばみられる良性骨腫瘍であり，多くは良性の経過をたどるが，まれに続発性に悪性転化することが報告されている．われわれは，全身のリンパ節腫大を伴いサルコイドーシスとの合併を認め，診断に苦慮した多骨性線維性骨異形成症に続発した骨肉腫の1例を経験したので報告する．

Sarcomatous transformation of fibrous dysplasia is extremely rare. We present the case of a 54-year-old man with multiple rib masses, multiple enlarged lymph nodes throughout the body, and multiple osteolytic lesions on computed tomography （CT）. A positron emission tomography （PET） scan showed abnormal enhancement in each. A needle biopsy of the right supraclavicular fossa lymph node revealed sarcoidosis. Considering the possibility of malignancy associated with sarcoidosis, a rib tumor resection and mediastinal lymph node biopsy were performed to confirm the diagnosis of the rib lesion. The pathology results showed that the rib mass was a low-grade central osteosarcoma and the mediastinal lymph node was sarcoidosis. The distribution of the lesions was consistent with osteosarcoma secondary to multiple fibrous bone dysplasia. As the osteosarcoma was low grade, the patient was followed up. Three years after surgery, there was no increase in residual disease.