Colonoscopy: An Increased Detection Yield?

The Emerging Concept of Nonpolypoid Colorectal Neoplasia

The frequent occurrence of flat or nonpolypoid neoplastic colorectal lesions has been reported recently in the Japanese literature, and also now in Western countries. In the large series collected by S. Kudo [1] [2] [3] at the Akita Red Cross Hospital in Japan, 45 % of early neoplastic lesions detected at colonoscopy were found to have a nonpolypoid morphology. The figure was only slightly lower (32 %) in the revisited results of the National Polyp Study in the USA [4]. In Japan, nonpolypoid lesions (adenoma or cancer) are classified as variants of superficial lesions of types 0-II, i. e. superficially elevated (0-II a), completely flat and flush with the surrounding mucosa (0-II b) or superficially depressed without frank ulcer (0-II c). In mixed types, both depression and elevation are present (II a + II c or II c + II a). Depressed lesions represent less than 5 % of all early neoplastic colorectal lesions.

There is no doubt that the endoscopic detection of nonpolypoid lesions will increase the yield of colonoscopy. The question is whether nonpolypoid lesions are important precursors of advanced cancer. In fact, most of these lesions have a weak evolutive potential: false-negative results for nondepressed and nonpolypoid lesions have no serious consequences. In contrast, depressed nonpolypoid lesions are highly evolutive, even when their size is small. False-negative findings for depressed lesions have severe repercussions, because these lesions often progress to advanced cancer. It is now considered that up to 40 % of advanced cancer cases arise from depressed lesions.

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