Clinical, Radiologic, and Pathologic Spectrum of Myositis Ossificans and Related Lesions: A Unifying Concept
Myositis ossificans (MO) is a designation that encompasses a heterogeneous group of lesions, all of which demonstrate heterotopic ossification. In addition to classic-appearing MO, the following are closely related entities osteoma cutis, a mature-appearing, localized ossification within the skin and subcutis associated with a variety of precipitating factors (i.e., trauma, neoplasm); florid reactive periostitis (fi-bro-osseous pseudotumor of the digits), a fibroblastic and osteocartilaginous prolif-erative lesion of the fingers and toes, especially the proximal phalanx, often associated radiographically with a laminated periosteal reaction; bizarre parosteal osteochon-dromatous proliferation (Nora's lesion), a hypercellular cartilage-capped exostosis surrounding an irregular mixture of bone and reactive fibrous tissue, most often arising from the juxtacortical surfaces of the middle and proximal phalanges of the hands and feet; Dupuytren's subungual exostosis, a fibrocartilage to hyaline cartilage exostotic proliferation morphologically resembling bizarre parosteal osteochondromatous proliferation but anatomically characterized by subungual distal phalangeal origin. As considerable clinical and histomorphologic overlap exists between MO and these: related entities and nosologic distinction appears to be based largely on anatomic and radiographic relationships, we propose the unifying term pseudomalignant heterotopic ossifications. These benign heterotopic ossifications must be distinguished from extraskeletal osteosarcoma.