3）超音波内視鏡による深達度診断

Endoscopic Ultrasonography, an Accurate Imaging Technique for the Diagnosis of Early Colorectal Cancer

要旨　早期大腸癌の精密画像診断法の中で，超音波内視鏡（EUS）は腫瘍を垂直断層像として描出でき，深達度を客観的に評価できる．早期大腸癌の中でpM癌やpSM-slight癌は，内視鏡的摘除の適応である．しかしpSM-massive癌は，リンパ節郭清を伴う外科手術が必要である．自験579病変でのEUSによる鑑別診断正診率は，90％と良好であった．特に通常内視鏡で深達度診断に迷う場合は，EUSを併用することが有用であると考える．しかし腫瘍の存在部位などによっては，EUSにより描出困難な場合がある．そこで3次元EUSが実用化され，診断精度の向上のみならず，描出困難病変の克服にも役立っている．早期大腸癌に対するEUS診断は解決すべき問題点も多いが，客観的な深達度診断法として重要な役割を担っている．

　EUS（endoscopic ultrasonography）, an accurate imaging technique for the diagnosis of early colorectal cancer, can provide vertical cross-sectional images and allows the depth of tumor invasion to be objectively evaluated. Among early colorectal cancers, endoscopic resection is indicated for the treatment of cancers confined to the mucosa（pM）or slightly invading the submucosa（pSM）on histopathological examination. However, colorectal cancer with massive invasion in the submucosa（pSM-massive）requires surgery with lymph-node dissection. Among 579 lesions that we studied by EUS, the rate of correct differential diagnosis was as high as 90%. In particular, when the depth of tumor invasion cannot be readily determined by conventional endoscopy, EUS should be concurrently performed. However, imaging of tumors was sometimes difficult with conventional EUS equipment, depending on location and other factors. Therefore, three-dimensional EUS has been developed, contributing not only to improved diagnostic accuracy, but also to overcoming the difficult-to-image lesions. Many problems remain in the diagnosis of early colorectal cancer by EUS. However, EUS plays an important role in assessing the depth of tumor invasion.