Bone
Fibrous and Fibroosseous tumors of bone
Myositis ossificans

Author: Nat Pernick, M.D. (see Authors page)

Revised: 25 October 2016, last major update November 2014

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PubMed Search: Myositis ossificans[title]
Cite this page: Myositis ossificans. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/bonemyositisossificans.html. Accessed December 8th, 2016.
Definition / General
  • Also called benign fibroosseous lesion (better term since may not involve muscle or inflammation), myositis ossificans circumscripta, heterotopic ossification
  • Benign, solitary, reactive fibroblastic proliferation with reactive bone formation
  • 50% have history of trauma, although often trivial
  • Rapid growth
  • May occur in hand (called florid reactive periostitis, fibroosseous tumor of digits, parosteal fasciitis)
  • Rarely associated with malignancy, but may be confused with malignancy (Hum Pathol 1975;6:653)
  • Rarely is generalized, associated with skeletal anomalies of hands and feet causing immobilization and death (see fibrodysplasia ossificans progressiva)
  • Rarely occurs within the abdomen (intraabdominal heterotopic ossification); usually men, mean age 61 years, with small bowel obstruction associated with heterotopic bone formation in small bowel mesentery after abdominal surgery (Am J Surg Pathol 1999;23:1464)
  • Sites: upper extremity flexors, quadriceps, thigh adductors, gluteal muscles, soft tissues of hand; usually near a bone
Radiology Description
  • Periosteal reaction and soft tissue calcification 3-6 weeks after injury, with replacement by heterotopic bone at 10-12 weeks
Radiology Images

Images hosted on Pathout server:

Lateral foot - contributed by Dr. Mark R. Wick

Treatment
  • Excision or conservative
Case Reports
Gross Description
  • 2-5 cm, well circumscribed, soft red-brown center, gritty periphery
  • Lesion often encased in shell of bone
Micro Description
  • Cellular stroma, new bone, rarely cartilage
  • Early- highly cellular with immature fibroblasts centrally, brisk mitotic activity, focal hemorrhage, resembles nodular fasciitis or osteosarcoma
  • Later- woven bone with large, plump, crowded osteocytes and myofibroblasts; process is zonal; lamellar pattern may develop over time; more mature peripherally with osteoblastic rimming
  • At 3 weeks, inner zone resembles nodular fasciitis, intermediate zone contains osteoblasts which deposit woven bone, outer zone contains mineralized trabeculae and eggshell type calcification
  • Bone marrow eventually fills intertrabecular spaces
Micro Images

Images hosted on Pathout server:

Contributed by Dr. Mark R. Wick

Electron Microscopy Description
  • Prominent myofibroblasts
Differential Diagnosis