Osteonecrosis of the jaw

Core idea: Exposed, non-healing jaw bone with chronic infection and necrosis, classically in patients on Bisphosphonate/denosumab or after radiotherapy.

Typical setting

• Older patient, malignancy or osteoporosis.
• History of:
  • IV bisphosphonate or denosumab (MRONJ), or
  • Head & neck RT (osteoradionecrosis).
• Trigger: recent dental extraction or chronic dental disease.
• Clue in request: “non-healing socket”, “exposed bone”, “persistent pain/swelling”.

Imaging features

Radiograph / OPG

• Often subtle / late:
  • Mixed lytic–sclerotic change in alveolar bone.
  • Poorly defined marrow lucency.
  • Irregular lamina dura, loss of normal trabecular pattern.
  • ± Sequestra (dense, dead bone fragment).
  • ± Pathological fracture.

CT

• Best for extent and sequestra.
• Findings:
  • Cortical destruction, patchy lysis, “moth-eaten” areas.
  • Sclerosis and cortical thickening of adjacent bone.
  • Sequestrum: dense, devascularised fragment with surrounding lucent rim.
  • Involucrum: thickened, sclerotic reactive bone.
  • Fistulae / sinus tracts, adjacent collections.
  • Mandible > maxilla (molar region, mylohyoid line).

MRI

• Marrow:
  • BME signal: Low T1, high STIR/T2 in active inflammatory phase.
  • Sclerotic signal: low signal on all sequences in chronic phase
• Soft tissue:
  • Mucosal thickening, soft tissue phlegmon/abscess, muscle oedema.
  • Helps exclude tumour recurrence in post-RT patients.

Nuclear medicine

• Bone scan: focal increased uptake in active disease, may be photopenic in fully necrotic sequestra.
• SPECT-CT: useful to confirm sequestra, guide surgery.

Key imaging differentials

• Osteoradionecrosis – similar imaging; history of RT field is decisive.
• Chronic osteomyelitis – may be indistinguishable clinically; drug/RT history helps.
• Recurrent tumour (H&N SCC) – mass-like soft tissue, nodal disease, PET-avid tissue.