印環細胞癌が主体であった表面型早期大腸癌の1例

The Superficial Type Early Colon Cancer, Mainly Composed of Signet-ring Cell Carcinoma, Report of a Case

要旨　患者は67歳の女性．既往歴として1992年7月に膵粘液嚢胞腺癌で膵体尾部，脾合併切除術を受けている（stageⅠ）．1993年12月，検診目的で施行した大腸内視鏡検査で，盲腸前壁に表面が発赤調で，一部にわずかな褪色面を有する約15mm大の扁平な隆起性病変を認めた．注腸X線検査では病変は明らかな陥凹面を有し，一部はなだらかに隆起し，sm浸潤癌を考えた．更に細径超音波プローブ検査でも粘膜下層への中等量の浸潤所見を認め，Ⅱc＋Ⅱa型の表面型大腸sm癌と診断し，回盲部切除術を施行した．病理組織学的には，粘膜内では高分化腺癌と印環細胞癌が混在し，粘膜下層では印環細胞癌が線維化を伴って中等量浸潤していた．本症例は術前の画像診断からsm中等量浸潤との診断が可能で，更に，内視鏡的に腫瘍表面のわずかな腿色面から印環細胞癌の可能性も考えられ，興味ある症例として報告した．

　Signet-ring cell carcinoma of the colon is uncommon, and its diagnosis in the early stage is extremely rare. A 67-year-old female was given a colonoscopic examination during a general check up. A flat elevated lesion with central depression was detected on the anterior wall of the cecum. Part of the tumor showed a gradual elevation suggesting submucosal involvement, and a slightly discolored area within the reddish tumor surface. Barium enema study confirmed a type Ⅱc＋Ⅱa lesion in the cecum, and a subtle deformity of the wall underneath the tumor. High-frequency ultrasonic probe with a sonoprobe system (20 MHz, Fujinon SP-501) showed a low echoic mass in the submucosal layer just under the gradually elevated region of the tumor. With the diagnosis of type Ⅱc+Ⅱa cancer with moderat extension to submucosa, the patient underwent a surgical resection of the ileo-cecal region. On the fresh specimen, the tumor was observed 12×8 mm in size. Histopathologically, the tumor was composed of signet-ring cell carcinoma and well differentiated adenocarcinoma. Signet-ring cell carcinoma was located in the slightly discolored area within the tumor, which had been observed by colonoscopic examination, and had spread diffusely with fibrosis in the submucosal layer under the gradually elevated region of the tumor.

　This case suggests that the possibility of signet-ring cell carcinoma should be taken into account when a tumor shows a discolored area, and that ultrasonography should be applied to detect submucosal invasion.