転移性脊椎腫瘍との鑑別を要した無症候性椎体骨折を伴ったsynovial cystの1症例

A Synovial Cyst Accompanied by Asymptomatic Lumbar Vertebral Fracture Requiring Differentiation from Spinal Metastasis

Ⅰ．はじめに

　腰椎synovial cystは，椎間関節や腰椎分離部から生じ，腰痛，下肢痛などの原因となることがある^1,4,8)．高齢者では，脊椎圧迫骨折を高頻度に生じるが，骨粗鬆症による圧迫骨折と癌転移による圧迫骨折との鑑別が重要である．今回，L5椎体に高度なfluorodeoxyglucose（FDG）集積を認め，転移性脊椎腫瘍を疑ったが，臨床経過，病理学的検査から無症候性腰椎圧迫骨折を合併した腰椎分離部synovial cystと診断した症例を経験したので報告する．

　We experienced a case with a synovial cyst accompanied by asymptomatic lumbar vertebral fracture that required differentiation from spinal metastasis. An 82-year-old man suffered from right leg and anal pain. Computed tomography（CT）showed L5 spondylolysis. Magnetic resonance images（MRI）revealed an intra spinal cyst and acute lumbar vertebral fracture of L5 vertebral body. The surrounding area of the cyst presented contrast enhancement, and the extradural mass compressed the dural sac. Bone scintigraphy with 99m technetium-MDP demonstrated intense uptake on the right first, fourth, fifth, and seventh ribs and L2, L3, and L5 vertebra. The F-18 fluorodeoxyglucose positron emission tomography（FDG-PET）image demonstrated an increased radiotracer uptake in the L5 vertebra（standardized uptake value（SUV）max＝3.5). Spinal metastasis was suspected. Because of the cauda equina compression syndrome, it was surgically removed. Intraoperatively, a well-demarcated extradural cyst was found and compressed the dural sac markedly. The cyst capsule was thin and contained clear, thin fluid with no signs of bleeding. The histological diagnosis was a synovial cyst. His neurological symptoms improved after the surgery. The synovial cyst may enlarge after asymptomatic vertebral fractures.