実験的小脳腫瘍—その超微像とmedulloblastomaの組織由来の検討

ELECTRON MICROSCOPE STUDY OF THE MEDULLOBLASTOMA AND THE EXPERIMENTAL CEREBELLAR GLIOMAS:With Special Referance to the Origin of Medulloblastoma

I．はじめに

　medulloblastomaは子供の小脳に発生する悪性の膠腫で，1925年Bailey and Cuohing^1）はこの腫瘍をmedul—loblastomaと命名するとともにこの腫瘍はspongioblastとneuroblastの2つの方向に分化する能力をもつ未分化な膠細胞"medulloblast"の腫瘍であると考えたが，この腫瘍の組織由来は今日でもまだあきらかにされていない。この腫瘍がObersteinerの外顆粒層細胞に，あるいは第4脳室壁を形成する後髄帆内に残存する未分化細胞の迷芽から発生するという考えが行なわれているほかに，この腫瘍の構成細胞の形態，組織構成が網膜や副腎に原発するneuroblastomaとまつたく類似する点から，この腫瘍がneuroblastomaであるという考えもある。いずれにしてもこの腫瘍が未分化な神経組織の腫瘍であるという点ではおおかたの意見は一致しているが，最近実験病理学者のなかにこの腫瘍が小脳皮質顆粒層の成熟神経細胞の腫瘍，neuroblastomaであるという説も提起されるようになり，この腫瘍の本態特に組織由来はますます不明確となつている。そこで数年来行なつてきた膠腫の実験的研究によつて得られた実験膠腫のなかで小脳発生腫瘍について病理組織学的，電子顕微鏡学的に検索するとともに，medulloblastomaの超微像を検索対照し，medulloblastomaの組織由来特に小脳顆粒層由来説について検討を加えた。

The origin and nature of medulloblastoma is still uncertain. Up to this time two main sources have been proposed as its origin. Some embryologists postulated an origin in fetal granular layer of Ober-steiner, while others in the remnants of embryonal cellular proliferation at the posterior velum. Electron microscope studies of medulloblastoma and experimen-tal induction of cerebellar tumors were made in order to inquire into this problem.

Twenty-nine tumors were obtained out of a total of 137 mice and rats which had received implanta-tion of carcinogenic chemical. The histological ap-pearance of the tumors in majority of cases closely resemble that of glioblastoma in man. There was no incidence of the tumor with the histology sugges-tive of human medulloblastoma. Electron microscope study was made on the experimental cerebellar tumors to supplement histological observations. The ultra-structural details of experimental gliomas were most mimic of glioblastoma in man.

To contrast and compare experimatal gliomas with gliomas in man, electron microscope observations of human medulloblastoma were made in 3 cases. They were made up of closely placed cells with relatively uniform fine cellular details. The nuclei were rounded. The cytoplasm was rather scant in relation to nuclear volume. They contained a consid-erbl number of RNA granules, scattered ergastoplasmic sacs and small mitochondria. The monotony of the ultrastructure of medulloblastoma is standing out in sharp contrast to divergent ultrastructure of individual tumor constituents of experimental gliomas. No tumors produced presents the fine structure equated withthat of medullobla stoma. The present study holds no proof that medulloblastoma is derived from the adult granule cells of the cerebellar cortex.