Periosteal Reaction

• Mineralized periosteal reaction = signal void on all sequences
• Subperiosteal tissue = isointense T1, hyperintense T2, enhances with gadolinium

Classification by Pattern (and Aggressiveness)

Fig. 40.4 - Types of periosteal reaction. (A) Solid - cortical thickening at medial femoral metaphysis (osteoid osteoma). (B) CT showing the nidus. (C) Multilaminated - humerus in sarcoma. (D) Codman triangle - Ewing sarcoma of humerus. (E) Sunburst spiculation - surface osteosarcoma. (F) Hair-on-end - proximal ulna sarcoma.

1. Solid (Non-aggressive)

• Appearance: Thick, uniform, well-formed single layer of new bone fused to the cortex
• Mechanism: Slow, successive deposition of compact lamellar bone; periosteal layers fuse over time
• Indicates: Slow-growing, chronic, non-aggressive process
• Causes: Stress fractures, medial tibial stress syndrome (shin splints), adductor insertion avulsion syndrome, osteoid osteoma, grade 2 chondrosarcoma
• Note: A solid reaction does not guarantee benignity

2. Lamellated / Multilaminated ("Onion-Skin") (Intermediate aggression)

• Appearance: Multiple parallel layers of periosteal new bone, like concentric rings of an onion
• Mechanism: Periodic or episodic growth causes successive lifting of the periosteum with new bone laid down in each cycle
• Indicates: Intermediate aggressiveness - subperiosteal extension of tumour, infection, or haematoma

Fig. 1.15 - Lamellar (onion-skin) periosteal reaction in an aneurysmal bone cyst of the fibula (arrows) - Imaging Anatomy, Vol. 3

• Classic causes: Ewing sarcoma (most classic), acute osteomyelitis, some benign masses (aneurysmal bone cyst)

3. Codman Triangle (Aggressive)

• Appearance: A triangular shell of reactive periosteal bone at the margin of the lesion, where the periosteum has been lifted and interrupted by the rapidly growing process. It represents the edge of subperiosteal tumour extension in the longitudinal direction.
• Mechanism: Tumour grows so fast it breaks through the periosteum, leaving a triangular residual shell at the proximal/distal limit
• Indicates: Rapidly evolving, aggressive process
• Classic causes: Osteosarcoma (most classic), Ewing sarcoma; not specific to any one tumour

4. Spiculated - Sunburst / Hair-on-End (Most aggressive)

• Appearance:
  • Sunburst: coarse, diverging spicules radiating outward from the cortex
  • Hair-on-end: fine, parallel vertical spicules perpendicular to the cortex
• Mechanism: The periosteum is elevated and disrupted by the pathologic process; osteogenesis occurs in the subperiosteal space perpendicular to the cortex, creating radial spicules
• Indicates: Most aggressive, rapidly evolving process
• Classic causes: High-grade osteosarcoma (sunburst), Ewing sarcoma, occasionally sickle cell disease / thalassemia (hair-on-end in diploe of skull)

Fig. 1.16 - Spiculated periosteal reaction in metastatic colon cancer to the right scapula

Summary Table

Other Contexts

• Osteomyelitis: periosteal reaction (often lamellated) accompanies osteolysis; MRI is optimal for demonstrating both periosteal reaction and bone marrow changes, and helps differentiate from infarction
• Sickle cell disease: osteolysis + periosteal reaction are early findings of bone infection
• Thyroid acropachy: solid periosteal reaction of the hands/feet in autoimmune thyroid disease (clubbing + digital swelling)
• Fracture healing: exuberant periosteal callus can mimic periosteal reaction
• Aseptic loosening (orthopaedic implants): outer cortical periosteal reaction along a stem tilted in the medullary canal suggests aseptic loosening