1H-MRSにおける定量解析が放射線壊死とanaplastic oligodendrogliomaの再発の鑑別に有効だった1例

Usefulness of Quantitative 1H-MR Spectroscopy for the Differentiation between Radiation Necrosis and Recurrence of Anaplastic Oligodendroglioma

Ⅰ．はじめに

　脳疾患の存在および形態的診断には，X-ray Computed Tomography（X線CT）やMagnetic Resonance Imaging（MRI）がその優れた空間分解能やコントラスト分解能により有用であるが，それらは腫瘍の活性度など，代謝情報や機能的情報に関しては多くを提供してはいない．Magnetic Resonance Spectroscopy（MRS）は，信号強度は低いが特異的な代謝物そのものからの信号が利用され，生体中の生化学情報を非侵襲的に検出して，種々の病態解析を行うことが可能な臨床上有用な診断ツールである．MRSの対象核種は数多く存在するが，臨床レベルで用いられているのは水素原子核（¹H）を対象とした¹H-MRSであり，¹H-MRSは脳梗塞^1,9)や脳腫瘍^5,19,24)の診断における有用性が報告されている．われわれは，これまでに¹H-MRSによる脳内代謝物の定量手法を確立し，脳腫瘍の悪性度評価を中心に検討を重ねてきた^14,17)．

　放射線壊死と腫瘍再発の鑑別は，脳腫瘍における治療方針を決定する上で重要な問題であるが，画像診断では困難な場合が多い．今回われわれは，放射線壊死とanaplastic oligodendrogliomaの再発の鑑別において¹H-MRSによる脳内代謝物の定量解析が有用であった症例を経験したので報告する．

　We report a case,in which quantitative ¹H-MR spectroscopy (MRS) was useful for the differentiation between radiation necrosis and a recurrent tumor. The present case is a 44-year-old man who underwent the subtotal removal of a mass lesion in the left frontal lobe. The histological diagnosis was anaplastic oligodendroglioma (WHO grade Ⅲ). Postoperatively,a fractionated radiotherapy (total 64Gy) and chemotherapy were performed. MRI after the radiotherapy showed no contrast enhancing lesion. MRI,5 years after the radiotherapy,showed a growing enhancing lesion and a T1 hypointensity lesion without enhancement,both of which indicated a recurrent tumor. MR spectroscopy was performed for the differential diagnosis of these lesions. The spectrum was acquired by the point resolved spectroscopy (PRESS) method by TR/TE＝2,000 ms/68 ms,136 ms,and 272 ms and evaluated with peak pattern and quantification value of metabolite. MRS of the enhancing lesion demonstrated a decrease of the Choline-containing compounds (Cho) concentration,disappearance of N-acetylaspartate (NAA),decrease of Creatine/ Phosphocreatine (t-Cr) and presence of Lipids (Lip) and Lactate (Lac),all of which are characteristic finding of a radiation necrosis. The histological diagnosis of this lesion showed evidence also of radiation necrosis. On the other hand,MRS of the T1 hypointensity lesion without enhancement showed,a marked high peak of the Cho concentration,which is characteristic for a recurrent tumor. The histological findings of this lesion showed a diffuse proliferation of recurrent tumor cells. Quantitative ¹H-MRS is a useful tool for the differentiation between radiation necrosis and recurrent tumors.