A case of implantation dermatosis that formed a tumor

A 51-year-old man visited our hospital complaining of a tumor located above his lip. He had been hit on his upper left lip by a chopstick holder 2 months previously. The lesion turned into a tumor and gradually enlarged. The tumor was well circumscribed, smooth and covered with reddish, partially milk-white skin. During surgery to remove the tumor, a piece of a chopstick was found in the subcutaneous tissue, and a diagnosis of implantation dermatosis (ID) was made. On histology, the tumor appeared as an abscess that had increased fibroblasts, small vessels and a large number of neutrophils. In the Japanese published work, we found 86 cases of ID; three were similar to our case and had been clinically diagnosed as adnexal tumors. There were also six cases that showed abscess formation similar to our case on histology. In a survey of the published work from other countries, there were 44 ID cases. There were no common features found among the cases reported in the published work.