| [ Summary ] |
Some flat adenomas spread extensively and circumferentially along the colonic wall although they are low compared with their large diameter of more than 10mm. We call these large flat adenomas laterally spreading tumors (LSTs). These lesions were classified into granular and non-granular types. Non-granular LSTs do not have nodules. Sometimes they have ill-defined pseudodepressions, which appear after dyespraying and are considered to be the LST pseudodepressed type. Morphologically, they are different from depressed car cinomas, which have well-demarcated depressions. The rate of submucosal invasion in the LST pseudo-depressed type is 17.0%, which is quite different from that in depressed carcinomas over 10mm in size (79.7%). Therefore, it is very important to distinguish between these two types by careful observation, using dye-spraying techniques to choose suitable therapies, such as EMR or surgery, colorectal flat or depressed lesions. However, the LST pseudo-depressed type is similar to the depressed type in terms of crypt(pit) pattern, histological findings, and genetic background. Rather straight glands, which grow vertically to the muscularis mucosae and small roundish or tubular crypt patterns on the surface (type IIIs) are seen in both types of colorectal tumors. |