小さな表面型大腸上皮性腫瘍の病理学的特徴―表面型（Ⅱa型）の判定基準を中心に

Pathological Characteristics of Small Superficial Type Epithetial Neoplasia of the Large Intestine with Special Reference to Its Macroscopic Criteria

要旨　従来当教室で用いてきた大腸上皮性腫瘍の肉眼型分類（旧分類）で，表面型（Flat型）と判定された病変の肉眼的特徴は“長径と高さの比≧3，かつ表面平坦（球形度≦1.2）”であり，その判定は，病変の“形”に注目して主観的に行われてきた．今回，客観的判定基準として，隆起性病変の中で3mm以下の高さのものをⅡa型と定義し，肉眼型の再分類（新分類）を行った，両肉眼型分類間で，表面型病変の出現頻度，担癌率を比較検討し，以下の結果が得られた．腺腫で，5mm以下で，旧分類のFlat型病変は22.4％，新分類Ⅱa型病変は91.3％を占めた．純粋癌では5mmより大10mm以下で，旧分類Flat型病変が58.8％，新分類Ila型病変が88.3％を占めた．5mm以下の病変の担癌率は，旧分類Flat型病変では，他の肉眼型と有意差はなく，新分類Ⅱa型病変ではI型病変より有意に低かった．5mmより大10mm以下では，旧分類Flat型病変はIp型より有意に高い担癌率を示し，Ⅱa型はⅠ型と有意差はなかった．肉眼型と担癌率との相関の点で，新旧分類の優劣はみられなかったものの，新分類では表面型の腺腫の初期形態，純粋癌の肉眼形態，の位置付けが明確となった．判定基準の客観性の観点からも，今後，大腸上皮性腫瘍の肉眼型分類を，高さの絶対値を基に行い，3mm以下の高さをⅡa型の判定基準とすることを提唱したい．

　The classification of the superficial type (flat type) neoplasias has been decided subjectively according to the gross configurations of the lesions. The macroscopic characteristics of flat-type neoplasias by our previous macroscopic classification proved to be as follows: -“Size/height≧3 and flat surface (sphericity≦1.2)”. We defined the superficial type (Ⅱa type) neoplasia as those showing the macroscopic height of more than 3 mm (proposed macroscopic classification), and we reclassified 421 epithelial neoplasias, less than 10 mm in diameter, of the large intestine.

　We made a comparison of the incidence and the malignancy rate of the superficial type neoplasias lying between the two macroscopic classifications. The incidence of f lat type adenoma less than 5 mm was 22.4%, and the incidence of Ⅱa type was 91.3%. The incidence of flat type pure carcinoma between 5 to 10 mm was 58.8%, and the (incidence of) Ⅱa type between 5 to 10 mm was 88.3%. The Flat type showed a malignancy rate not significantly different to Is and Ip type in sizes less than 5 mm, and significantly higher than Ip type in sizes between 5 to 10 mm. The Ⅱa type showed a malignancy rate significantly less than that of I type in sizes less than 5 mm, and not significantly different among those between 5 to 10 mm in size.

　From the results, we concluded that the proposed classification better explains the initial macroscopic manifestations of adenomas, and characteristics of pure carcinomas. So we proposed the macroscopic criterion of the superficial (Ⅱa type) type as those with a height of less than 3 mm.