CT colonographyの現状と展望―大腸ポリープ・癌の描出

CT Colonography : Screening and Staging for Colorectal Carcinoma

要旨　multidetector-row CT（MDCT）を利用した腸管の三次元表示法であるCT colonography（virtual colonoscopy法）での大腸癌の存在診断は表面型病変で61.5％の描出率であった．また，注腸二重造影像に近似したdouble-contrast CT colonography像での病変の側面変形像の描出率は85％であり，深達度sm_2・3癌の正診率は89.3％で，内視鏡切除のための深達度診断の指標としては有用であった．CT colonographyは，撮影時間は短時間で苦痛が少なく，体位変換が困難な患者でも検査が可能で，各種の表示法を組み合わせると，1回のスキャンで大腸癌の存在診断，病期診断をすることができ，診断・治療の効率化に有用である．

　Recently, CT colonography (Virtual colonoscopy method) has become one of the useful procedures for colorectal imaging. Though it is possible to visualize exophytic polyps and carcinomas, it is important also to be able to visualize flat lesions. In this study, 61.5% of the flat lesions are visualized retrospectively.

　Concerning the staging of colorectal cancer, to diagnose the invasive depth is important for determining a therapeutic procedure. It is especially important to diagnose massive submucosal invasive (sm_2・3) carcinomas. To diagnose indentation in the profile image of a lesion, double-contrast CT colonography (DCCT), which is similar to a double-contrast barium enema study, shows 89.3% accuracy for diagnosis of massive submucosal invasion.

　In addition, CT colonography by multiplanar-reconstruction image or maximum-intensity-projection image can diagnose lymph node metatasis more clearly at one scanning. CT colonograph might be a useful procedure for screening and staging for colorectal carcinoma.