高周波超音波細径プローブ検査でsm浸潤距離を誤診した大腸sm癌の1例

Submucosal Colon Cancer in which Submucosal Invasion Depth was Misdiagnosed by High-frequency Ultrasound Probes, Report of a Case

要旨　患者は76歳，女性．下部消化管内視鏡検査でS状結腸に径1.5cmの無茎性隆起を認めた．隆起表面に易出血性の陥凹面を認めたことからsm浸潤癌を疑い高周波超音波細径プローブ検査（HFUP）を行った．HFUPで病変は第1層から第3層深部に達する低エコー領域として描出され，内部エコーは不均一で最深部および辺縁部にcystic echoを示す部分が認められた．深達度sm³，sm垂直浸潤距離2,600μm，一部にmucinous componentを有する浸潤癌と診断した．病理組織学的には，大部分が粘膜内にとどまる高分化型腺癌で，ごく一部でsm微小浸潤を認めるのみであった（sm垂直浸潤距離100μm）．粘膜下層に著明な血管増生および線維化を認めたことから，HFUPではこれらの組織所見を癌浸潤と見誤ったものと考えられた．今後，内視鏡治療の適応基準をsm垂直浸潤距離1,000μmへと拡大するにあたって，より精度の高い深達度診断が要求されるなか，本症例のように線維化を伴う例にどのように対応していくかが今後の課題であると考えられた．

　In a 76-year-old woman, colonoscopy revealed a sessile tumor of the sigmoid colon with a depression on its surface. By using high-frequency ultrasound probes (HFUP), a hypoechoic and heterogeneous mass, which extended to the submucosal layer, was detected. Furthermore, anechoic areas were also shown around the mass by HFUP, leading to the suspicion that the tumor with its mucinous component had invaded the submucosal layer massively. The submucosal invasion (sm-invasion) distance on HFUP was evaluated as 2,600μm. A sigmoidectomy was performed. Pathologically, the tumor was a well differentiated adenocarcinoma with minute sm-invasion (sm-invasion distance on the histological specimen was evaluated as 100μm). Fibrosis and abundant vessels were found in the submucosal layer of the specimen, suggesting that these pathological characteristics had caused the misdiagnosis of sm-invasion distance on HFUP. For accurately evaluating sm-invasion distance of colorectal cancers by HFUP, it is necessary to discriminate between submucosal fibrosis and tumor invasion.

　1) Third Department of Internal Medicine, Asahikawa Medical College, Asahikawa, Japan