胃癌の超音波内視鏡診断

Endoscopic Ultrasonographic Diagnosis of the Depth of Invasion of Gastric Cancer

　胃癌の超音波内視鏡による深達度診断について述べた．早期胃癌のうちUL(－)病巣では，第3層の画然とした破壊を認めるものはSM癌と診断する．UL(＋)病巣では，UL-II，III，IVの潰瘍・潰瘍瘢痕と同様のEUS像を示すものをM癌と診断する．一方，先細り状に収束するSM層先端が画然と断裂，あるいは胃壁が肥厚するものはSM癌と診断されている．UL(＋)病変では，M癌の診断基準はかなりコンセンサスが得られているが，SM癌の診断解釈が多少各者で異なる．進行胃癌は境界明瞭な腫瘤を形成する腫瘤型と，腫瘍境界が不明瞭で，第3，4層の肥厚が主体をなす壁肥厚型に大別される．進行胃癌では胃壁の基本層構造のうち，第4～5層の破壊の程度により深達度を診断する．さらにEUSは内視鏡でSM2～MPと診断された病巣において，①陥凹型早期胃癌で内視鏡による深読みを補正する，②IIc様進行胃癌で内視鏡による浅読みを補正するのに有用である．

　EUS is efficacious for diagnosing the depth of cancerous invasion.

　In early gastric cancer without ulcers or ulcer scars, involvement of the third layer is interpreted as submucosal invasion. In early cancer associated with ulcers or ulcer scars, the tumor echo is usually associated with a fan-shaped hypoechoic shadow and tapering interruption of the third layer. Destruction of the tapering submucosal layer or thickening of the wall is interpreted as submucosal cancer.

　The advanced cancers are divided into two types based on EUS findings. In the mass-forming type, cancer was detected as a mass with a clear margin with concomitant destruction of the layered structure. In the wall-thickening type, the layered structure remained relatively intact and remarkable thickening of the gastric wall is noted. The depth of invasion is diagnosed according to the degree of destruction of the fourth or the fifth layer.

　EUS is useful for depressed type early cancer lesions, whose depth of cancerous invasion is endoscopically diagnosed as SM2～MP, to correct the depth of invasion to M～SM1．

　EUS is useful for IIc-like advanced cancer lesions, whose depth of cancerous invasion is endoscopically diagnosed as SM2～MP, to correct the depth of invasion to SS～.