Soft tissue

Fibroblastic / myofibroblastic

Myositis ossificans

Topic Completed: 1 June 2013

Minor changes: 20 January 2021

Copyright: 2002-2022,, Inc.

PubMed Search: Myositis ossificans [title] soft tissue

Daniel Wimmer, M.D.
Jerad M. Gardner, M.D.
Page views in 2021: 11,196
Page views in 2022 to date: 608
Cite this page: Wimmer D. Myositis ossificans. website. Accessed January 19th, 2022.
Definition / general
  • Focal intramuscular lesion composed of cellular fibrous tissue and metaplastic bone
  • Also called benign fibro-osseous lesion or heterotopic ossification (perhaps more accurate terms since may not necessarily involve muscle or inflammation)
  • In subcutis, called panniculitis ossificans; in fascia or tendons, called fasciitis ossificans
  • Various forms: circumscripta (localized, either traumatic or atraumatic) or progressiva (also called fibrodysplasia ossificans progressiva, an autosomal dominant inherited disorder with progressive crippling ossification involving muscle groups over time, eMedicine)
  • Related entities:
    • Fibro-osseous pseudotumor of digits: similar entity to myositis ossificans but more superficial and distal; affects fingers of older adults with occupations that require repetitive manual use (Ann Diagn Pathol 2008;12:21), less likely to contain fibrinous material (Int J Surg Pathol 2003;11:187)
    • Panniculitis ossificans: similar histologic features but involves subcutis rather than muscle
  • Usually physically active young males with rapid growth of mass
  • 60 - 75% have history of trauma in prior 4 - 6 week
  • May also occur after elective surgery, severe burns, neurological injury
  • Upper extremity flexors, quadriceps, thigh adductors, gluteal muscles, soft tissues of hand
Radiology description
  • Xray: periosteal reaction with eggshell calcification at periphery 3 - 6 weeks after injury; recommended to review Xrays before diagnosis
Case reports
  • Excision, although may regress without treatment; rarely recurs if incompletely excised
Clinical images

Contributed by Mark R. Wick, M.D.

CT scan (left two) and MRI (right two)

Images hosted on other servers:

Various images

Gross description
  • Well circumscribed, soft center, gritty periphery, usually 3 - 5 cm (but may be as large as 15 cm)
Gross images

Case #449, contributed by Sajna V.M. Kutty, M.D.

Case #449

Images hosted on other servers:

Bone fragment from abdominal wall

Microscopic (histologic) description
  • Cellular stroma with new bone, atypia and mitotic figures, rarely cartilage; zonation often present, although zones may be poorly demarcated
  • Early lesions (3 weeks): inner cellular zone resembling nodular fasciitis with short fascicles or haphazard fibroblasts that are uniform with faint eosinophilic cytoplasm, tapering processes, vesicular or finely granular nuclei and variable nucleoli, usually numerous mitotic figures but none atypical; stroma is vascular, myxoid or edematous with extravasated red blood cells, fibrin, scattered inflammatory cells and osteoclast-like giant cells; if highly cellular, may mimick sarcoma such as osteosarcoma; intermediate zone has osteoblasts depositing woven bone, and outer zone has mineralized trabeculae
  • Later: bone matures with formation of marrow and myofibroblasts are less prominent
Microscopic (histologic) images

Case #449, contributed by Sajna V.M. Kutty, M.D.

Case #449

Contributed by Mark R. Wick, M.D.

AFIP images

Fibroblastic and myofibroblastic cells in center of lesion resemble nodular fasciitis, with nuclear uniformity

Osteoid is broader than in osteosarcoma

Osteoid undergoing mineralization

Mature bone at periphery, fibrous tissue resembling nodular fasciitis at center, osteoid in between

Osteoblasts have
large nuclei with

Nuclei are
enlarged but
not pleomorphic

Images hosted on other servers:

Various images of thigh lesion

Cytology images

Images hosted on other servers:

Hip mass with FNA

Positive stains
  • Fibroblasts and myofibroblasts express vimentin and variable actin and desmin, osteoclasts express vimentin
Electron microscopy description
  • Fibroblasts and myofibroblasts have dilated rough endoplasmic reticulum and aggregates of cytoplasmic filaments variably associated with dense bodies; osteoblasts have numerous mitochondria and abundant dilated rough ER
Molecular / cytogenetics description
Differential diagnosis
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