Radiographic diagnosis of early colorectal cancer, with special reference to the superficial type of invasive carcinoma.

The possibility of radiographically diagnosing carcinoma with submucosal involvement (invasive carcinoma) is discussed based on 119 invasive carcinomas of the large bowel that had been treated surgically and colonoscopically over a period of 9 years (1989-1997) at the Cancer Institute Hospital in Tokyo. Of these lesions, 38 were superficial-type invasive carcinoma, accounting for 31.9% (38/119) of all invasive colorectal carcinomas, including 36 lesions (94.7%, 36/38) of types IIa and IIa + IIc and 2 lesions (5.3%, 2/38) of type IIc + IIa. No pure type IIc was seen. The radiographic images obtained were correlated with macroscopic findings and analyzed in terms of visualization of the lesion's contour, central depression, converging folds, and basal indentation. A definitive diagnosis of superficial invasive carcinoma can be made radiographically if a lesion measures 10 mm and reveals moderate to severe basal indentation in a complete or nearly complete profile radiographic image. Attention should be paid to the presence of superficial-type advanced carcinomas measuring 10 mm or less, which is not infrequently experienced in Japan. Polypoid invasive carcinoma can be definitively diagnosed in the same way with much more certainty than can the superficial type because few polypoid advanced carcinomas are less than 20 mm. The size and the radiographic sign of the basal indentation are the most important indicators for the diagnosis of invasive carcinoma.