─早期胃癌の診断の基本─超音波内視鏡診断

Endoscopic Ultrasonographic Diagnosis of Early Gastric Cancer

要旨●超音波内視鏡検査（EUS）では正常胃壁は5層に描出され，消化管内腔より第1〜2層が粘膜層，第3層が粘膜下層，第4層が固有筋層，第5層が漿膜下層と漿膜層である．潰瘍瘢痕（ulcer scar ; UL）0型早期胃癌では第3層の画然とした破壊を認めるものはSM深部浸潤癌と診断する．UL1型早期胃癌では，腫瘍とULのエコーレベルはほぼ同一のため診断は困難で，いくつかの分類が提唱されている．ESDの普及と高齢化の進行により，癌の深達度診断だけでなくESDによる一括完全切除が可能かどうかという診断もEUSに求められている．第3層の描出不能距離が5mmを超えると，標本の挫滅・切り込みが起こりやすく，ESDの技術的難易度は極めて高く，治療法の選択には慎重な判断が求められる．

　EUS（endoscopic ultrasonography）depicts the normal gastric wall as a five-layer structure. The first and second layers are regarded as the mucosal layer, the third as the submucosal layer, the fourth as the proper muscle, and the fifth as the subserosal layer and serosa when the third layer has been obviously destroyed, early gastric cancers without ulcerous changes are diagnosed as those with massive submucosal invasion. Diagnosis of depth of invasion of cancers with ulcerous changes is still difficult because the echoic levels of the tumor and the ulcerous changes are almost the same, although several classifications have been proposed. Diagnosing whether complete en-bloc resection is possible via EUS has been necessary because of the aging of the population and the prevalence of ESD. When the length is >5mm, in which case EUS cannot clearly depict the submucosal layer, en-bloc resection by ESD is very difficult and careful judgment is necessary when deciding a treatment plan.