Florid reactive periostitis ossificans of the distal ulna.

: Florid reactive periostitis is the term used to describe a benign disease characterized by aggressive periosteal reaction and benign soft-tissue inflammation. Although it is considered rare, there are numerous reports in the literature that refer to this disease with different names such as parosteal fasciitis, fasciitis ossificans, benign fibro-osseous pseudotumor, pseudomalignant osseous tumor of soft tissue, and bizarre parosteal osteochondromatous proliferation. As a result, the nomenclature is confusing, and some authors have placed florid reactive periostitis ossificans into the heterogeneous group of pseudomalignant osseous tumors of soft tissue or proliferative periosteal processes, whereas other authors place this entity in the myositis ossificans group. In the same manner, florid reactive periostitis has been considered to be a previous stage of bizarre parosteal osteochondromatous proliferations. This article presents a case of florid reactive periostitis ossificans of the distal ulna in a 13-year-old boy. The patient presented with a painful lesion in the distal ulna, and plain radiographs suggested the presence of a quickly growing periosteal lesion with associated calcification and soft tissue mass. Histologically, the appearance was that of reactive periostitis. The clinical, radiological, and histologic features of florid reactive periostitis are described.