5) 拡大内視鏡による腫瘍の組織型診断

Histopathological Diagnosis of Gastric Tumors by Magnifying Endoscopy

要旨　胃癌はその組織型により発育進展の様相や生物学的悪性度が異なるため，検査や治療法の選択を行ううえで組織型診断は非常に重要である．組織型診断を行ううえで，通常内視鏡観察による肉眼型や色調が重要だが，通常内視鏡観察のみでは組織型の判断を誤ることもある．ズーム式拡大内視鏡やNBIが開発され，微細な表面構造や血管構造の観察が可能となった．表面構造と微細血管パターンの変化は，腫瘍・非腫瘍の鑑別や腫瘍の進展範囲診断に加え，組織型診断の一助となる．高～中分化型腺癌では，表面構造として密に増生したpit patternや絨毛様構造を呈し，微細血管パターンとしてnetworkを形成する口径不同，走行不整な血管増生を認める．分化度が悪くなるに従い構造の不整が増しnetworkは崩れてくる．一方，低分化型腺癌では，表面構造は無構造を呈し，微細血管パターンはnetworkを形成せず細かく縮れた異常血管が増生する．ただし，拡大内視鏡による所見は，肉眼型や表面びらんの有無により異なるため，通常内視鏡診断を含めた総合的診断が重要となる．

　Histopathological diagnosis is essential for appropriate planning of the course of treatment or further examinations required for gastric cancer patients, as the malignant potential or direction of development are mainly determined by histopathological types. Although macroscopic findings, such as color or appearance of the lesions, obtained by conventional endoscopy are important, histological evaluations by these methods may be difficult and carry a risk of misdiagnosis.

　The development of zoom endoscopy or narrow band imaging (NBI) has enabled close observation of the surface structures or vascular patterns. The findings of alternation of surface structures or vascular patterns allow differentiation between cancer and non-cancer tissue, can distinguish the borders of the carcinoma lesion, and facilitate histological estimation.

　Well-differentiated carcinoma shows a pattern of dense pits or villous appearance on the surface, increased vessels of varied diameter, or an irregular vascular network. As the carcinoma progresses, structural irregularities increase and lead to loss of the vascular network. On the other hand, poorly differentiated carcinoma has no definite structure on its surface and produces thin abnormal vessels without forming a vascular network.

　Thorough inspection by conventional endoscopy is required, because the findings of magnifying endoscopy vary with the macroscopic pattern of the tumor or surface erosion on or around the tumor.