Unusual Osseous Metaplasia in Colonic Polyp: Two Case Reports and Review of the Literature

Background: Osseous metaplasia occurring within the gastrointestinal tract is a rare phenomenon. Only a few of cases have been documented that osseous metaplasia can occur in colorectal polyps, although its underlying pathogenesis has not yet been elucidated. Methods: Two cases of osseous metaplasia within inflammatory and adenomatous polyps of colon, respectively. The clinical and histological features of this lesion, as well as suggested mechanisms for its pathogenesis are discussed. Results: Under the histological examination, both cases demonstrate the typical normal-looking osseous trabeculae rimmed by a layer of scattered osteoblasts in the stroma of inflammatory polyp or tubular adenoma of colon. To the best of our knowledge, they are possible the first cases of osseous metaplasia in colorectal polyps in Chinese. Conclusion: Although it has not been found to have any significance in clinical treatment and prognostic evaluation, our data suggest that persistent inflammatory process and/or pluripotent stromal cells in polyps might contribute to the formation of osseous metaplasia in colonrectal neoplastic and non-neoplastic polyps.