脳白質の血管―その構築と形態について

Architecture and morphology of the blood vessels in the cerebral white matter.

I．はじめに

　臓器としての脳がもつ著しい特異性に関連していると思われるが，これまでその脳を養う血管に関する研究は枚挙にいとまがない。それらは正常と病的状態を扱い，また形態，機能，代謝などの多くの面を検討している。したがって，これらの中には，当然「脳白質の血管」に焦点を当てた研究が数多くあるに違いない，と思われてくる。しかし実際には，そのような研究論文はきわめて少ないことに驚かされる。それは，神経細胞の存在する大脳皮質を含む灰白質とミエリンに囲まれた軸索の存在する脳白質との間の基礎的研究対象としての興味の差の現われかもしれない。一方，脳白質を侵す病態（多発性硬化症，leukodystrophyなど）のもつ特殊性とも関係しているかとも思われる。

　本稿では，しかしながら，「脳白質の血管」，ここでは大脳白質の血管，についてこれまでの形態学的研究を可能な限りまとめてみたい。

We reviewed the architecture and morphology of the blood vessels in the cerebral white matter, since these aspects have received little attention in previous studies.

With regard to the architecture of the cerebral medullary arteries, the studies of Kawahara (1960), Van den Bergh (1969) and De Reuck (1971) are considered to be important in helping to clarify the mode of blood supply to the cerebral white matter. There were no significant differences in ultra-structural features between the arterioles and capillaries encountered in the cerebral white matter and those in the cerebral grey matter, although it is clearly evident at the light microscopic level that the density of the former is much lower than that of the latter. It is known that cerebral blood vessels receive dual sympathetic and parasympathetic innervation, which may play an important role in neuro-genie control of cerebral blood flow. However, such knowledge has been obtained exclusively from observations of the cerebral major arteries and pial arteries as well as the arterioles and capillaries in the cerebral grey matter. It is still uncertain whether the blood vessels in the cerebral white matter also receive such innervation. Senile morphological changes in human medullary arteries have recently been studied intensively by Furuta et al. (1991). According to them, sclerotic change involving fibro-hyaline thickening of the wall is a prominent feature in the cerebral medullary arteries, especially those in the deep white matter, but is not evident in arteries of the basal ganglia and thalamus, or the cerebral cortex. Thus, specific processes related to aging may occur in the cerebral medullary arteries.