いわゆる"arachnoidal sarcoma of the cerebellum"（desmoplastic medulloblastoma）—組織由来，およびclassical medulloblastomaとの臨床的比較

SO-CALLED ARACHNOIDAL SARCOMA OF THE CEREBELLUM ITS HISTOGENESIS AND CLINICAL COMPARISON WITH CLASSICAL MEDULLOBLASTOMA

Ｉ．緒言

　1939年，FoersterとGagelが^8），　medulloblastomaとよく似てはいるが，これと異なる小脳原発の悪性腫瘍として，"das umschriebene Arachnoidealsarkom desKleinhirns"の3症例を報告して以来，同様な腫瘍を"（circumscribed） arachnoidal sarcoma of the cerebel—lum"^12）16）"circumscribed sarcoma of the cerebellum"11），"cerebellar sarcoma"^27），"arachnoidal sarcoma"^29），などとして報告され，この腫瘍の独立した存在は広く認められてきた。これに対し1964年になり，RubinsteinとNorthfieldは^19），この腫瘍は"desmoplastic medul—loblastoma"と呼ぶべきmedulloblastomaの一亜型であるとした。以後，この腫瘍のmedulloblastoma説に同意する報告もでてきたが^{3,4,7,10,24,26）}，最近でも髄膜腫の亜型である可能性を主張する報告や^22），sarcomaに分類する成書もあり^29），いまだ最終的な結論は出ていないと考えられる。

　著者らは，九州大学医学部脳神経外科，および九州中央病院脳神経外科において，いわゆる"arachnoidalsarcoma of the cerebellum"の3症例を経験した。この腫瘍の組織由来について，組織学的，電子顕微鏡的に検索し，またこの腫瘍と従来のmedulloblastomaとを臨床的事項について比較検討する。

Three cases of cerebellar tumor named "arach-noidal sarcoma of the cerebellum" or "desmoplastic medulloblastoma" were reported. Histologically, this tumor is characterized by islands of cells sur-rounded by and delineated from the rest of the tumor cells. In the island, there are no reticulin fibers, while the tumor tissue surrounding the islands demonstrated an elaborate network of reti-culin fibers. The tumor cells in the island are essentially identical with the cells of classical medulloblastoma under light as well as electron microscope. By electron microscopic observation, each group of the tumor cells was encircled and separated from the connective tissue element by a basement membrane. From these findings, the tumor called "arachnoidal sarcoma of the cerebel-lum" or "desmoplastic medulloblastoma" should be of neuroectodermal origin.

This tumor was discussed from clinical stand point comparing with classical medulloblastoma. The authors did not find any difference between this tumor and the classical medulloblastoma in age distribution, location, tendency to encapsulation and in consistency. The prognosis of both tumors was thought to be better in adults than children, and desmoplastic medulloblastoma seemed to have a slightly favorable prognosis than the classical medulloblastoma.