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Codman triangle

MSKRadiograph / CT

A triangular ossified cuff of elevated periosteum at the margin of a bone lesion, where new bone forms only at the edge of the raised periosteum.

What it means

Aggressive periosteal reaction, indicating a fast-growing bone lesion.

Mechanism

A rapidly expanding lesion lifts the periosteum so quickly that new bone ossifies only at the peripheral angle, forming the triangular cuff.

Associated conditions

  • Osteosarcoma
  • Ewing sarcoma
  • Osteomyelitis
  • Subperiosteal haematoma

Pearls

  • A Codman triangle indicates an aggressive process but is not specific for malignancy.
  • Infection and trauma can occasionally produce the same appearance.

References

  • Radiopaedia: Codman triangle

For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.