早期大腸癌の深達度診断におけるEUSの有用性―通常内視鏡診断との比較：EUSを重要視する立場から

Usefulness of Endoscopic Ultrasonography (EUS) Compared with Colonoscopy for Diagnosing the Depth of Invasion of Early Colorectal Carcinomas

要旨　EUSを施行した早期大腸癌99病変を対象に，EUSの深達度診断能を通常内視鏡（CS）診断と比較した．EUSによる病変描出率は83.8％，描出例での深達度正診率は88.0％であった．EUS描出例でのCSによる深達度正診率は80.7％とEUSより低率であった．形態別の正診率は隆起型，表面隆起型では差はなく，陥凹型でのみEUSがCSに比し高率であった．CSで誤診した15病変中10病変をEUSで正診しえた．その10病変のうちCSで深達度を過大評価し，EUSで正診しえた病変は全例表面型で，逆にCSで過小評価しEUSで浸潤をとらえることにより正診した病変は全例隆起型であった．深達度正診率からみると陥凹型でのみEUSの併用がより正確な深達度診断につながると言えるが，隆起型でも表面構造が保たれた病変ではCS，拡大内視鏡での深達度診断が困難な場合があり，EUSの併用がより有効であると考える．

　We compared the usefulness of endoscopic ultrasonography (EUS) for diagnosis of early colorectal carci-noma with that of colonoscopy (CS). The subjects consisted of 99 lesions. Evaluation by EUS was possible in 83.8% (83/99). The diagnostic accuracy rate of EUS was higher than that of CS (88.0% vs 80.7%). The diagnostic accuracy rate of EUS for protruding and flat elevated lesions was almost the same as that of CS, but the diagnostic accuracy rate of EUS for depressed lesions was higher than that of CS. 10 out of 15 lesions misdiagnosed by CS were properly diagnosed by EUS. All of the lesions overdiagnosed by CS were flat elevated lesions and all of the lesions underdiagnosed by CS were protruding lesions. As for the accuracy rate, combination of EUS with CS was useful for evaluation and diagnosis of tumor invasion especially in depressed lesions. However, EUS is also more helpful for the diagnosis of protruding lesions with regular surface structure, because it is sometimes difficult to diagnose the depth of invasion of these lesions by CS or magnified colonoscopy.