大腸腫瘍性病変の肉眼形態分類

Macroscopic Classification of Early Colorectal Carcinoma

要旨　早期大腸癌の肉眼形態分類は，早期胃癌との整合性を考えて規約されてきたが，内視鏡やpit pattern診断などの診断学の進歩とともに陥凹型早期癌，顆粒集簇様病変やLSTなど新しいカテゴリーの症例の発見，Ⅲ型病変が認められない現状，臨床に反映されないなど矛盾が指摘されている．そこでわれわれはシンプルかつ臨床的に意味のある分類として発育進展の視点から考えた．すなわち腺腫由来の隆起型病変とde novoの陥凹型病変とに分け，更に隆起型

病変は発育方向の違いでprotruded type，LSTを含めたflat typeに分けた．また陥凹型病変は浸潤様式で形態が異なるが，連続性を考えた．以上よりprotruded type，LSTを含めたflat type，depressed typeの3つに大きく分類することを提唱し，その分類が臨床的にも妥当である点について説明した．

　Macroscopic classification of early colorectal carcinoma, which based on the definition of early gastric carcinoma, was defined in 1977. After development of modern endoscopic diagnosis, we were able to gather much data about macroscopic features, for example depressed type of lesion, granular lesion, LST et al. On the other hand, despite the fact that this classification included type Ⅲ lesions such as gastric carcinomas, we have never been able to discover one yet.

　We would like to point out some inconsistencies in this “classical” classification and we consider that a new one is called for. Consequently we wish to propose a new macroscopic classification from the viewpoint of growth and development ; protruded type, flat type and depressed type. 1) Protruded types, which originate as adenoma and grow upwards, include sessile and pedunculated lesions (Is, Isp, and Ip) . They indicate mainly type ⅢL and Ⅳ in pit pattern diagnosis. Cancer rate among them is 10.3%, and invading rate is 2.0%. Therefore the majority of them are adenoma. 2) Flat types include small lesions (Ⅱa, Ⅱb, and Ⅱa ＋ dep) and laterally spreading tumors (LST), and their elevation is very low. They originate in adenoma, but LST especially spread laterally. They indicate type ⅢL and Ⅳ pit pattern and are thus similar to protruded type. 3) Depressed types (Ⅱc, Ⅱc ＋ Ⅱa, Ⅱa ＋ Ⅱc and Ⅰs ＋ Ⅱc), which originate in de novo cancer, grow downwards. Cancer rate and invading rate of this type is higher than that of other types. Type Ⅱc and Ⅱc ＋ Ⅱa change into type Ⅱa ＋ Ⅱc and Ⅰs ＋ Ⅱc according to the degree of their invading volume.

　Consequertly, we considered that the macroscopic classification of early colorectal carcinoma should signify a characteristic of the lesion. As our classification is simple, it is our view that it deserves serious considiration.