Pediatric Myositis Ossificans

• Etiology:
  — Inflammatory pseudotumor of skeletal muscle
  — Aberration of muscle repair due to disordered satellite cell differentiation
  — Can be post-traumatic (direct trauma) or non-traumatic (burns, immobilization, neurologic dysfunction) or genetic
• Imaging:
  — Zone phenomenon with center being fibroelastic, periphery being osteoblastic, rim being calcified, surrounding edema
  — Early proliferative stage at 2-3 weeks after injury shows active vascular and cellular proliferation manifesting as soft tissue mass that may have agressive features such as intense perilesional soft tissue and marrow edema or ill-definition or periosteal reaction
  — Intermediate calcification and ossification phase at 3-7 weeks shows mass composed primarily of fibroblasts
  — Mature ossification phase at 6 or more weeks shows peripheral ring of mature ossification surrounding a central acellular core
• Imaging MRI:
  — In early phase see peripherally isointense T1 signal and hyperintense T2 signal and enhancement corresponding to peripheral osteoid matrix
  — In late phase after 8 weeks see peripherally hypointense T1 signal and hypointense T2 signal and no enhancement
• DDX:
• Complications:
• Treatment:
• Clinical:
  — Usually in adolescents and young adults, not typical in less than 10 years old
  — Post-traumatic most common type which most commonly affects extremities (quadriceps femoris and brachialis muscles)

Radiology Cases of Myositis Ossificans