小脳テントに発生したClear Cell Meningiomaの1例

A Case of Clear Cell Meningioma Originating from the Cerebellar Tentorium

I．はじめに

　Clear cell meningioma（CCM）はWHO新分類に新しい腫瘍概念として登場した髄膜腫の稀な一亜型であるが^4）その症例報告はいまだ少ない．腫瘍細胞はグリコーゲンに富みwhorl patternやstriform patternなどの配列を持たず細胞質が明るく抜けているのが特徴的である^1,9）．その臨床病理像については，脊髄硬膜内や後頭蓋窩に多く発生し，組織学的には良性ながら局所再発や浸潤性格が強いことを指摘した報告も見られる^11）．

　今回われわれは小脳テントに発生したCCMの1例を経験したので文献的考察を加え報告する．

We report herein on a case of clear cell meningioma originating from the cerebellar tentorium, surgicallytreated by occipital transtentorial approach (OTT).

A 67-year-old woman was admitted to our hospital in September, 1996, complaining of gait disturbance.MRI revealed an isointense mass on T1 and T2 Wl, clearly enhanced with gadolinium in the right uppercerebellum originating from the tentorium, A left vertebral angiogram showed tumor stain from the rightsuperior cerebellar artery. The tumor was subtotally removed by OTT on September 24,1996. Gammaknife radiosurgery was performed for regrowing tumor 6 months after surgery.

Histological examination revealed that the tumors were composed of sheets of clear, glycogen-rich cellsand lobulated by thin connective tissues, There were no malignant findings, but some tumor cells had infil-trated into the cerebellar cortex. Immunohistochemistry showed that tumor cells were positive for EMAand vimentin, but negative for keratin. MIB-1 staining index was 7.02%. From these findings, this case wasdiagnosed as a typical clear cell meningioma originating from the cerebellar tentorium.

From a review of the literature including our case, clear cell meningioma may be clinicopathologicallymalignant, so careful follow-up will be necessary.