ヒト下垂体における扁平上皮細胞巣（squamous cell nest）の電顕的研究

AN ULTRASTRUCTURAL STUDY ON SQUAMOUS CELL NESTS OF HUMAN PITUITARY

　抄録　ヒト下垂体隆起部にしばしば見出される扁平上皮細胞巣を電顕的に検索した。材料は59歳女性の，乳癌による疼痛に対する下垂体切除術から得られた。扁平上皮細胞巣は完全に基底膜で囲まれ，種々の扁平上皮細胞から成るが，時に腺性下垂体実質細胞を含む。扁平上皮細胞は基底細胞層の細胞と棘細胞層の細胞とに分けられる。前者（基細胞と総称）の多くは切れこみの強い核膜，tonofibril，よく発達したdesmosomeを持つ。後者はこれらに加えて細胞間橋を有する事が特長で，前者から分化してきたものである。扁平上皮細胞巣に接して腺性下垂体を構成するacinusがあり，それは分泌顆粒を持つ腺性下垂体実質細胞と少数のstellate cellおよびまれにfollicular cellから成る。基細胞と腺性下垂体実質細胞との間の中間型は認められなかったので，基細胞が既存の腺性下垂体実質細胞のdirect metaplasiaによって生じたものであるとは言えない。一方基細胞とstellate cellの形態的類似性，stellate cellを含む腺性下垂体実質細胞が構成するacinusと扁平上皮細胞巣との密接な位置関係，および扁平上皮細胞巣が年齢と共にふえるというこれまでの報告と合わせて，基細胞はstellate cellに由来するものと考えられる。

The squamous cell nests which appear to have developed in the base of pars tuberalis are studiedelectron microscopically. A fresh pituitary was obtained from a 59-year-old white woman, who underwent hypophysectomy to reduce the pain due to the breast cancer.

Each squamous cell nest was completely enclosed by the basal lamina, consisted of squamous cells, and sometimes contained adenohypophyseal paren-chymal cells. The squamous cells were classified into cells in the basal layer and those in the spinous layer with intercellular bridges. Most of the former cells (B cells) possessed a nuclear mem-brane of strong interdigitation, well-developed desmosomes and tonofibrils. Adjacent to the squamous cell nests, there were acini which con-sisted of adenohypophyseal parenchymal cells, a few agranulated stellate cells, follicular cells inrare cases.

As no transitional types between the B cells and the adenohypophyseal parenchymal cells were observed, B cells may not be said that they have been formed through the direct metaplasia of existing adenohypophyseal parenchymal cells. In view of the morphological similarities of the earliest B cells to the stellate cells, of the close positional relationship between the squamous cell nests and the acini and between the adenohypo-physeal parenchymal cells and the squamous cells, and of the past reports that squamous cell nests increase in number with aging, B cells appear to originate from the stellate cells.