早期胃癌のEUS診断―機種による差はあるのか

Endosonographic Images of Early Gastric Carcinoma: From the Viewpoint of Instruments

要旨　内視鏡的超音波断層法（EUS）を用いた胃癌深達度診断では，機器の改良によって詳細で明瞭な断層像の観察が可能となっている．すなわち，振動子の高周波数化や観測装置の改善は病変超音波像をより組織ルーペ像に近い形で表示できるようになった．従来，無エコーに近い低エコー層として内部エコーの評価に限界のあった画像も低エコー実質層として表現できるようになっている．この描出能は内視鏡治療の対象となる早期病変診断の客観的な情報として活用できるであろう．しかしながら，機器の改善に対し，自験例における癌深達度判定は改善の一途をたどっているとは言えない．診断基準の改訂を求めるのも1つの方法だが，連続像による診断や，分解能の高い画像の自動解析など新しい解析手法の開発が求められる．

　Endosonographic diagnosis of the depth of early gastric carcinoma invasion was evaluated from the viewpoint of instruments. Based on the advances of technology, ultrasound endoscopes and monitor units have been improved rapidly leading to a higher accuracy rate of diagnosis of depth of carcinoma invasion and beautiful pictures. Some factors, such as frequency of scanner, width of scanner, and monitor unit influence the images. EUS pictures obtained by various types of ultrasound endoscopes and monitor units have become beautiful and precise, depending on the frequency of the scanner.

　Accuracy rate of the diagnosis of depth of carcinoma invasion obtained by instruments at each period are almost the same, around 80％. The causes of misdiagnosis are the lack of skill in maniplating the ultrasound endoscopes or lack of experience in interpreting EUS images or the lesions being conplicated with ulcerative fibrosis. This means that the accuracy rate concerning the depth of carcinoma invasion does not necessarily depend on advanced instruments which can produce beautiful images.

　For obtaining a higher accuracy rate, trials to make new criteria for judging the depth of carcinoma invasion or obtaining serial images of the lesion, or instruments with high powered auto-analytic ability are desirable.