微細構造よりみた松果体腫瘍の組織発生

ULTRASTRUCTURAL STUDY OF PINEALOMA IN VIEW OF ITS HISTOGENESIS

I．はじめに

　松果体部に発生し，組織学上大型上皮様細胞と小型リンパ球様細胞よりなる，いわゆる"two-cell pattern"を示す松果体腫瘍は，その組織像の特異さにより他の原発性脳腫瘍と明らかに様相を異にし，組織発生に関して多くの論議を呼んできた。

　さらにectopic pinealoma （異所性松果体腫瘍）という腫瘍形の存在は，組織発生論をさらに複雑かつ解明困難なものにしてきた。

The tumor, originating from the pineal gland, isusually composed of large cells with clear cytoplasmsand small ones with hyperchromatic nuclei, and iscalled "pinealoma with two-cell pattern". Thehistogenesis of pinealoma has widely been discussed,but remains in question. To analyze the histo-genesis of pinealoma, the author studied the ultra-structure of 13 cases of tumors, which histologicallyrevealed "two-cell pattern" pinealomas.

Results:

1. On a series of electron-microscopic pictures, dif-ferentiation of large cells was definitely observedin various stages. According to these findings,large cells were divided into the following fivegroups.

A: Undifferentiated cells.

B: Differentiated cells.

I: Cells similar to the pineal primordium de-rived from the diencephalic roof of the thirdventricle in developmental stage. Structuralfeatures of this stage are the basement-membrane, the junctional complex, and themicrovilli.

II: Cells similar to the pineal bud.

III: Cells which have structural features of pinealphotoreceptor cells in low vertebrates.

IV: Cells which have structural features ofmammalian pineal parenchymal cells, such as the club-shaped cell process, the micro-tubule and the smooth endoplasmic reticulum.

With the ultrastructural characteristics of largecells, it can be conjectured that the large cellcomponent of pinealoma originates from the pinealparenchymal cells.

2. Small cells in pinealomas are identified as lympho-cytes and plasma cells. The lymphocytes show auniform stage of differentiation, but the plasmacells show various stages of differentiation expressedin the patterns of the endoplasmic reticulum.There is a perivascular accumulation of lympho-cytes and plasma cells. These findings are similarto those of the lymph-node after the injection ofthe antigen. Therefore, the following conclusionappears to be justified : the proliferation of lympho-cytes and plasma cells is an expression of theimmunological response in pinealomas.

3. The melatonin synthesizing enzymes, HIOMTand SAT, which are active in normal maturedpineal parenchymal cells, were examined in threecases, but were not detected. This finding suggeststhat tumor cells, which have more or less immatureor undifferentiated components under ultrastructuralstudy, can not produce the melatonin.