三次元超音波内視鏡による胃癌深達度診断―特にSM1胃癌の診断能について

Diagnosis of Gastric Cancer Invasion with Three-dimensional Endoscopic Ultrasonography, Especially in Cases with "SM1" Invasion

要旨　超音波内視鏡は，それまでの粘膜表面からの深達度診断から，断層像による深達度診断をもたらした．一方，胃癌の内視鏡治療に関しては，近年のITナイフ，Hookナイフ，Flexナイフなどの機器の開発と粘膜切除の適応拡大という機運と相まって，粘膜下層剥離術（ESD）が急速に臨床の場で広まっている．この適応決定において粘膜下層への500μmの浸潤の診断は，臨床上重要な問題である．これに対して連続断層面が自動的に撮影可能な三次元超音波内視鏡3D-EUSによる胃癌深達度診断成績は，潰瘍非合併群において，SM浸潤500μm以下群では56.7％（17/30），500～1,000μm群は77.8％（21/27），1,000～2,000μm群は86.7％（26/30），2,000＜μm群は91.4％（32/35）で，全体では78.7％（96/122）と500μmを超えると80％前後以上の成績であり，臨床上の要求をある程度満足できており，内視鏡治療術前の検査として施行されるべきと考えられた．しかしながら，潰瘍，あるいは潰瘍線維化合併例においては，線維化内への微小浸潤の診断は困難であり，今後の新しい診断技術の開発を待たざるを得ないのが現状である．

　Endoscopic ultrasonography has introduced diagnosis based on transactional image to evaluate gastric cancer invasion after endoscopic diagnosis based on changes of mucosal findings. Concerning endosopic treatment of gastric cancer, IT knife, Hook knife, and Flex knife etc., which have been invented recently, have resulted in increasing endoscopic submucosal dissection for gastric cancer treatment and has widened the indication for endoscopic therapy. In order to indicate candidates for endoscopic treatment, it is clinically important to diagnose more or less than 500μm of submucosal invasion (SM1). Using 3D-EUS, it is practicable to diagnose small invasion of more than 500μm to the submucosa with consecutive transactional radial images and reconstructive linear images. The diagnostic accuracy of 3D-EUS is 56.7％ (17/30) in 0 IIc, IIa＋IIc, IIa, and I cases with submucosal invasion less than 500μm, 77.8％ (21/27) in 500～1,000μm cases, 86.7％ (26/30) in 1,000～2,000μm cases, and 91.4％ (32/35) in 2,000＜μm cases. Therefore examination of gastric cancer invasion with 3D-EUS is recommended before endoscopic treatment is undertaken. However differentiation between tiny gastric cancer invasion of ulcer fibrosis and ulcer fibrosis alone has been problematic, so we have to invent another new technique to enable differentiation between such lesions.