Abstract
CT colonography, which consists of helical scanning with multi detector CT (MDCT) that uses volume data, was performed for small (less than 20mm diameter) and invasive colorectal cancers. 11 patients underwent the study after total colonoscopy as preoperative examination confirming one lesion in each patient (types : IIa＋IIc ; 4, type2 ; 4, IIa ; 1, IIc ; 1, Isp ; 1) . The type IIa lesion, so called laterally spreading tumor (LST) , coexisted with advanced cancer.
All patients could undergo CT scanning immediately after colonoscopy. A complete 3-dimension image examination lasted about 15 minutes in all cases and there were no complications. All elevated lesions such as type2, IIa＋IIc, and Isp were visible regardless of size with CT colonography. However, superficial type tumor and depressed type tumor were undetectable.
CT colonography was considered to be a useful non-invasive examination to detect colorectal elevated lesions in a short time. In USA, the procedure has been recently introduced for screening of colorectal cancer as a replacement of colonoscopy. The idea is based on a widely known concept of the adenoma-carcinoma sequence. In Japan, CT colonography is being used to reinforce the endoscopic and radiologic diagnosis. Presently, CT colonography is not considered as ideal procedure for screening in Japan because it is unable to detect superficial and depressed type tumors. However, once CT scanning is performed we can gain enough information about the lesion such as accurate location, direct invasion to the surrounding organs, presence of lymph node metastasis and distant metastasis. Marking with clip during endoscopy, the location of superficial or depressed type tumors also will be evident.
As a preoperative examination along with colonoscopy, CT colonography might replace the barium enema examination.
