Ⅱa型の内視鏡診断

Endoscopic Diagnosis of Ⅱa Type Early Gastric Carcinoma: Protruding Type of Early Gastric Carcinoma

はじめに

　胃の隆起性病変は，レントゲンおよび胃カメラの進歩にともなって近年数多く発見され，生検の導入により術前診断が組織のレベルで可能となってきた．その結果，いたずらに癌をおそれて手術をすることが少なくなってきたことはよろこばしいことである．ここでは，今まで経験してきた胃隆起性病変の中で主としてⅡa型について内視鏡診断を中心に検討してみたいと思う．Ⅱa型早期癌の症例を検討するにあたって，Ⅰ型早期癌と，どの線で区別するかということと，Ⅱa＋Ⅱc型早期癌をどのようにとりあつかうかということが問題になる．

　Ⅱaの定義は粘膜の厚さの約2～3倍の高さをもつ隆起性早期癌とされており，それ以上のものをⅠ型早期癌と定めている．このことからⅡa型というと「小さい」というイメージと「扁平である」というイメージが浮かんでくる．したがって，大きくて扁平であるものに遭遇すると，どちらに入れようかとまどうことがある，しかし，その区分は各人各様で，あまり神経質になる必要もないと思うので，適当にとりあつかうことにした．次のⅡa＋Ⅱc型であるが，潰瘍性病変の存在が認められるものを除外して，Ⅱaから生じたのではないかと思われるⅡa＋Ⅱcを検討の対象として組入れることとした．Ⅱa＋Ⅱcの成因については，①Ⅱb→minute Ⅱa＋Ⅱc→Ⅱa＋Ⅱc，②Ⅱa→Ⅱb＋Ⅱc ③Ⅱb→minute Ⅱc→Ⅱa＋Ⅱcの経路が，内視鏡的な経過観察から認められており，また，佐野はこのⅡa＋Ⅱc型の組織学的分類をこころみ，Initial lesionとして①flat polyp ②Ⅱb ③潰瘍あるⅡcの三群に分け①をadenomatous type ②を更に二つに分けdepressed typeと潰瘍のないsubmucosal typeとし，前者はⅡaのたかまりが癌で示されているもの，後者は粘膜を癌が下からもち上げているものとしている．③は潰瘍のあるsubmucosal typeである．実際，その発生経過を推定することは困難であるが，潰瘍の合併しているものは除外してⅡa＋Ⅱc型も検討することにした．

　したがって，ここに検索の対象としてあげたのは，粘膜下腫瘍26例28個，腺腫性ポリープ127例187個，Ⅰ型早期癌52例55個，Ⅱa型早期癌21例27個，Ⅱa＋Ⅱc型早期癌23例23個である．

　Two ways of classification have been tried for protruding lesions of the stomach according to their configurations as seen in the profile and frontal views. The profile views of protruding lesions have been divided into four types: (1) gently sloping, (2) sessile, (3) subpedunculated and (4) pedunculated types. The frontal views have been classified into nine types. They are (1) round, (2) gourd-like, (3) mulberry-like, (4) elliptical, (5) club-like, (6) serpentine, (7) roundish, (8)irregu1ar-shaped and (9) centrally depressed types. Details of profile view have already been published (Stomach and Intestine, 2).

　In the latter classification, round and elliptical types were mostly benign; in the gourd-like type was atypical epithelium often seen. The mulberryshaped type was frequently of Ⅱa, and the club-like and serpentine types were often of I. The irregularshaped and centrally depressed types were seen in the malignant protruding lesions.

　Some features of Ⅱa type early gastric carcinoma are: (1) in most instances it is a fiat, broad-based plateau-like elevation sharply circumscribed against surrounding areas, (2) belonging to sessile type in the first classification and to either mulberry-shaped, irregular-shapecl or centrally depressed type according to the second. (3) The surface is uneven and irregular, sometimes granular and sometimes nodular, with its color mostly pale White or grayish white. Although erosion or bleeding is seldom seen on its surface, either can be seen in a having submucosal invasion where central depression is also apt to occur. (4) Differentiation from ATP depends on the size, type and surface irregularity. The Ⅱa must be taken into account when a lesion is more than 2cm in diameter, of irregular shape, or when the surface of the mucosa is small nodular, or further, when protrusions are of varying sizes and irregular-shaped. The Ⅱa must also be suspected when erosions are seen or when the center of elevation tends to be depressed. (5) It is often seen in the mucosa of atrophic gastritis associated with intestinal metaplasia; more often observed in older people. The gastric juice shows either hypoacidity or anacidity even when the stomach is stimulated with gastrin. The Ⅱa often appears as multiple lesions. This fact must always be borne in mind in the endoscopic examination of early gastric carcinoma.