Colorectal counterpart of gastric depressed adenoma. A comparison with flat and polypoid adenomas with special reference to the development of pericryptal fibroblasts.

The histological features of 28 depressed adenomas (DAs) were compared with those of 40 flat adenomas (FAs) without a central depression and those of 29 polypoid adenomas (PAs), with special reference to the development of pericryptal fibroblasts (PCFs), using immunohistochemical staining for muscle-specific actin (HHF-35). The DAs were composed of a crowded collection of adenomatous tubules with smaller diameters than those of the PAs. With regard to PCF development, the DAs had poorly developed PCFs; PCF (-), (+), and (++) numbered 12 (43%), 16 (57%), and 0 (0%), respectively. On the other hand, the nondepressed adenomas (PAs and FAs) had well-developed PCF; PCF (-), (+), and (++) numbered 5 (7%), 35 (51%), and 29 (42%), respectively. In addition, the number of PCFs seemed to decrease in the sequence of PAs, followed by FAs and DAs. According to our results, the DAs had a characteristic histological architecture together with poorly developed PCFs features, which distinguished them from the PAs. In conclusion, the depressed adenomas were considered a subtype of the flat adenomas. The depletion of PCFs seems to correlate with the depressed growth of the adenoma.