後頭蓋窩巨大脳石症の1例

A Huge Idiopathic Brain Stone in the Posterior Fossa

I．はじめに

　従来より頭蓋内異常石灰化巣に関する報告は数多くなされているが，石灰化の原因疾患が明らかにされることが通常である．一方，石灰化巣の病因が病理学的にも不明である場合にはidiopathic brain stoneと診断せざるを得ないが，かかる例の報告は極めてまれである．今回われわれは，病理組織学的にいわゆるidiopathic brain stoneと診断した後頭蓋窩巨大石灰化腫瘤の1例を経験したので，若干の文献的考察を加え報告する．

We report a case of idiopathic brain stone occurring in the posterior fossa. A 72-year-old woman with a huge calcified mass in the posterior fossa on plain cra-niogram was referred to us. She had suffered from in-tractable tinnitus and mild cerebellar ataxia for twenty years. CT scan revealed a dense bony mass in the post-erior fossa. Angiogram only showed an avascular huge mass in the posterior fossa. MRI clearly revealed the shape, heterogenous composition and anatomical rela-tion to the surrounding structure of the mass. The mass was totally removed uneventfully under ABR and SEP monitoring. The patient was discharged with improve-ment of subjective symptoms. The mass was histologi-cally diagnosed as an idiopathic brain stone because its components were mainly calcified tissues and collagen fiber of unknown etiology; no viable cells were found in any of the specimens. Idiopathic brain stones are very rare and only eight cases have been reported in the literature. The etiology and clinicl symptoms of this condition are briefly discussed.