Positron emission tomography（PET）による髄膜腫の循環代謝の評価

POSITRON EMISSION TOMOGRAPHY (PET) STUDY IN PATIENTS WITH MENINGIOMAS

　髄膜腫5例の腫瘍部，近接部および遠隔部の循環と酸素・糖代謝量をPETで測定し，年齢の相応した正常人およびグリオーマ例と比較検討した。腫瘍部のrCBF・rCBVは近接部および対側灰白質と比較して有意に高値であり（それぞれP＜O．01，P＜0.05），脳血管撮影およびCT所見を定量評価した。腫瘍部のrOEFは対側灰白質と比較して低下し，需要以上の血流がみられた。rCMRO²は対側灰白質と同程度でグリオーマと比較してrCMRO²／rCMRG1比が高く，髄膜腫では嫌気性解糖が少ないと考えられた。髄膜腫近接部における循環代謝は対側灰白質に比較して低下していたが，rOEFは0.51±0.13で，対側灰白質とほぼ同様の値であった。一方，グリオーマではrOEFが0.44±0.12と低下しており，髄膜腫と異なった動態を示した。対側灰白質のrCBF，rCMRO²およびrCMRG1はグリオーマと同様に正常人と比較して低下しており，rOEFの上昇から頭蓋内圧亢進に起因した病態が考えられた。

Regional hemocirculation and metabolism were evaluated in five patients with meningiomas using positron emission tomography (PET). Histological diagnoses were : two cases of meningotheliomatous type, one hemangiopericytic type, one fibroblastic type, and one transitional type. Regional cerebral blood flow (rCBF), blood volume (rCBV), oxygen extraction fraction (rOEF), and metabolic rates of oxygen (rCMRO₂) and glucose (rCMRG1) were measured with ¹⁵O₂, C¹⁵O.¹⁵O₂, and 18F-fluoro- deoxyglucose tracers. For the quantitative analysis, regions of interest were delineated on tumors, the peritumoral region, and the contralateral graymatter in comparison with age-corresponding 5 malignant gliomas and 5 normal volunteers. Tu-mor hemocirculatory parameters (rCBF : 57.2±. 22.6 ml/100 ml/min, rCBV : 7.95± 3.27 ml/100 ml, mean + SD, n= 5) were markedly higher than those of the contralateral gray matter (p ＜O.05 by a Student-t test). The high values were consistent with angiographic findings of tumor staining and with abundant tumor vessels demonstrated by pathological examination. rCMRO₂ was 2.15± 0.80 ml/100 ml/min, which were comparable to those of the contralateral gray matter. Tumor rCMRG1 showed 4.76±2.37 mg/100 ml/min ; the values of two cases were similar to the respective gray matter. The raised metabolic rate (rCMRO₂/ rCMRG1) therefore suggests rather aerobic gly-colysis as compared with gliomas. Low rOEF (0.26± 0.16) reveals an excessive blood flow be-yond oxygen demand of the tumor. In the peri-tumoral regions, rCBF and metabolism fell slightly but rOEF reached a level similar to the contra-lateral gray matter, possibly due to hemocirculatory stasis caused by intracranial hypertension ; in contrast, an unmatched reduction of rCBF and rCMRO₂ implies tumor cells infiltration in gliomas.

PET can provide us in vivo quantitative know-ledge of hemocirculatory and metabolic perturba-tion in patients with meningiomas.