Myositis Ossificans

**Semantic type:** Neoplastic Process

**Definition:** A self-limited benign neoplasm characterized by a zonal architecture. It is composed of spindle cells oriented randomly or in short intersecting fascicles. Peripherally, the spindle cells merge with osteoblasts that rim and populate ill-defined trabeculae and sheets of unmineralized woven bone, which is surrounded by well-formed trabecular and cortical-type bone that remodels into lamellar bone. Treatment is usually simple excision. Prognosis is excellent; recurrence is uncommon. (WHO 2020)