未分化型胃粘膜内癌の術前診断―X線診断

Diagnosis of Undifferentiated-type Early Gastric Carcinoma by X-ray

要旨　胃癌治療ガイドラインによると，未分化型胃癌は内視鏡治療の適応ではないものの，Gotodaらの報告をもとに，リンパ節転移の可能性が低いとされる2cm以下で潰瘍のない粘膜内癌は適応拡大として内視鏡治療が行われているのが現状である．治療適応の決定に必要な，深達度と潰瘍合併および腫瘍径の術前X線診断は厳密な正確さが要求されることから，未分化型癌の病理組織学的な浸潤や進展形式の特徴を踏まえ診断する必要がある．未分化型癌は腫瘍径20mmで約半数が，また潰瘍を合併した40％強がSM浸潤であることから，比較的小さくても浸潤および潰瘍合併に留意し，精密検査や読影をすることが重要である．一方で，非癌の被蓋上皮を残しつつ粘膜内を側方に進展する病変は，IIb類似もしくは随伴IIbの形態を示し，これらはごく微細なX線所見であり，診断が困難な場合がある．さらに，背景粘膜が中間帯や萎縮領域に存在する病変は，胃小区模様の差としてとらえにくいことや，混在型癌は境界範囲が不明瞭となりやすい傾向があることなどから，範囲・進展診断には細心の注意が必要である．

　Abstract Endoscopic surgery is not commonly indicated for cases of undifferentiated carcinoma according to the Japan Gastric Cancer Association guidelines. However, mucosal carcinomas＜2 cm in diameter with no ulceration, which are thought to have very low risk of lymph node metastasis, are treated endoscopically as an extended indication in accordance with the report of Gotoda et al.（2000）. On x-ray examination, accurate evaluation of size and depth of carcinoma as well as ulcerationtaking into consideration the features of histopathological invasion or extension for undifferentiated carcinoma are required to determine indication for endoscopic operation. As approximately half of all undifferentiated carcinomas are ≧2 cm in diameter and also more than 40% of carcinomas with ulceration show submucosal invasion, precise assessment and interpretation regarding invasion or ulceration are indispensable for even small undifferentiated carcinomas. On the other hand, cases of type IIb disease or that accompanied by type IIb lesions, which are characteristically intramucosal laterally spreading and spare the non-carcinomatous surface epithelium, are difficult to recognize on xray examination. Moreover, it is essential to accurately estimate the tumor borders and progression of carcinoma because lesions in the intermediate zone or atrophic mucosa are difficult to discriminate against the background of the gastric area, and mixed type lesions tend to have obscure borders.