Sub-classification of type VI pit patterns in colorectal tumors: relation to the depth of tumor invasion

We analyzed pit patterns of colorectal tumors with magnifying colonoscopy, focusing on the relationship between the VI pattern sub-classification and the depth of tumor invasion. The VI pattern was divided into the well-demarcated and poorly demarcated subtypes. The percentage of tumors with a depth of invasion of over 1,000 µm was in the order of non-V types (type I-IV) < type VI < type VN. Most well-demarcated VI lesions (80.8%) showed a depth of invasion of <1,000 µm compared to only 21.1% of poorly demarcated VI lesions. Both the frequency of degeneration or prolapse of the epithelial lining and the frequency of desmoplastic reaction occurred in the order of non-V types < type VI < type VN, while the degree of histological differentiation and the frequency of residual muscularis mucosae occurred in the order of non-V types > type VI > type VN. Furthermore, the poorly demarcated VI subtype showed a higher frequency of epithelial lining degeneration or prolapse and a lower frequency of residual muscularis mucosae than the well-demarcated VI subtype. Tumors with a depth of invasion of >1,000 µm showed a higher frequency of epithelial lining degeneration or prolapse, a lower degree of histological differentiation, a higher frequency of desmoplastic reaction, and a lower frequency of residual muscularis mucosae than did tumors with <1,000 µm of invasion. These results suggest that VI pit pattern sub-classification is a useful indicator of the depth of colorectal tumor invasion and treatment selection. A prospective study on this subject would be useful.