神経膠腫が疑われる無症候性FLAIR高信号病変の自然経過

Natural History of Patients with Asymptomatic FLAIR High-signal Lesions Suspected of Lower-grade Gliomas

Ⅰ．はじめに

　近年，脳ドックなどのスクリーニング頭部MRIの普及により，神経膠腫が疑われる無症候性のFLAIR高信号病変が発見される機会が増えてきている．『脳ドックのガイドライン2019』¹⁴⁾では，神経膠腫を疑わせる病変が発見された場合，PET/CTなどの追加検査を行い，神経膠腫が強く疑われる場合は，手術により組織診断を確定させることが推奨されている．また，疑診例にはgadolinium（Gd）造影MRIを行い，さらに2，3カ月後に再検査を行い，脳梗塞との鑑別をすることも推奨されている．しかしながら，Gd造影効果のない無症候性のFLAIR高信号病変の自然歴は不明な点が多く，短期間に悪性転化する症例の報告もあり，その治療方針やfollow up間隔・期間などについては一定の見解が得られていない^4,20,21)．

　神経膠腫が疑われるFLAIR高信号病変に対する当科の方針は，症候性であれば精査の後に摘出術あるいは生検術を行い，一方，無症候性であれば画像経過観察を行い，経過観察中に病変の増大を認めるか，症候性となった場合には手術を施行している．

　今回，当科における無症候性のFLAIR高信号病変の自然経過を報告し，症候性病変との比較，およびその治療方針やfollow up間隔などにつき検討を行った．

　The distribution of MRI scans has increased the chance of diagnosing asymptomatic FLAIR high-signal lesions. Herein, we retrospectively analyzed 14 asymptomatic FLAIR high-signal lesions to evaluate their natural course. Fifteen symptomatic（epilepsy）patients with FLAIR high-signal lesions were also analyzed as controls. As a result, all symptomatic patients underwent surgery and were diagnosed with lower-grade gliomas（n＝14）and a dysembryoplastic neuroepithelial tumor（n＝1). Among the 14 lower-grade gliomas, 11 gliomas were isocitrate dehydrogenase（IDH）-mutant. As previously reported, these results showed that FLAIR high-signal lesions with epilepsy are closely associated with IDH-mutant gliomas. On the other hand, 12 of the 14 asymptomatic patients showed no changes in the size of the lesion and symptoms during the follow-up period. Only 2 patients（14.3%）revealed increased lesions within 38 and 25 months, who were diagnosed with high-grade gliomas. Although there was no difference in the apparent diffusion coefficient value between asymptomatic and symptomatic lesions, low-intensity T1WI on MRI might be useful to discriminate lower-grade gliomas from non-tumor lesions.

　In conclusion, there is no need for immediate surgery for true asymptomatic lesions；however, we must undergo routine follow-up MRI scans.