中心前回の手の領域に発生したhigh grade astrocytomaの1例

A Case of High Grade Astrocytoma Arising in the Hand Area of Precentral Gyrus

要旨　症例は23歳男性で，左中心前回の手の領域に発生した小病変により，右小指の筋力低下から始まり，環指，次いで中，示，母指の順に大脳皮質一次運動野のhomunculusにしたがって知覚低下を伴わない進行性の運動麻痺を示した。病変はmagnetic resonance imaging（MRI）のT1強調画像で低信号域，T2強調画像で高信号域を示し，gadolinium増強効果は陰性であった。脳血管撮影，thallium scintigramでは異常を認めず，proton magnetoresonance spectroscopy（P-MRS）でN-acetylaspartateの低下とcholineの上昇を，diffusion-weighted image（DWI）でapparent diffusion coefficient（ADC）値の低下を認めた。ナビゲーション下開頭生検術によりhigh grade astrocytomaと診断した。悪性神経膠腫初期の小病変において，術前のP-MRSやDWIを併用したmulti-modalityの画像診断が有用であった。

Abstract

　A 23-year-old man presented with the right upper monoparesis. The right little finger paresis was apparent at first, and ring finger two weeks later, and middle, index, thumb were simultaneously four weeks later. Then the monoparesis gradually progressed to the proximal upper limb. Magnetic resonance imaging showed a small lesion at the knob of the left precentral gyrus. The lesion was low-intensity on T1-, and high-intensity on T2-weighted images, and clearly detected on high-intensity on FLAIR images, but showed no enhancement by gadolinium-diethylenetriamine pentaacetic acid （Gd-DTPA）. Angiography and thallium scintigraphy showed no remarkable findings. Proton MR spectroscopy demonstrated lower N-acetylaspartate （NAA） and higher choline （Cho） level compared to the contralateral cortico-subcortical area. Diffusion weighted images demonstrated low apparent diffusion coefficient （ADC） value and high intensity on b＝1,000. To clarify the diagnosis of the lesion, we performed open biopsy by using the neuronavigation system to detect the lesion accurately and minimize the biopsy. Histological examination revealed an high grade astrocytoma with high MIB-1 index over 30％. The progressive symptoms were due to highly infiltrative and proliferative nature of the tumor arising in the focal hand area of the primary motor cortex, according to the homunculus. We discuss herein the neuroimagings of the case that was considered to be in the initial stage of a malignant tumor.

（Received : February 17, 2005）