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Halo sign

ChestCT

A pulmonary nodule or mass is surrounded by a rim of ground-glass opacity, like a halo.

What it means

Perilesional haemorrhage, classically around an angioinvasive fungal infection in the immunocompromised host.

Mechanism

Vascular invasion causes infarction and haemorrhage into alveoli around the central necrotic nodule, producing the ground-glass rim.

Associated conditions

  • Invasive pulmonary aspergillosis
  • Other angioinvasive fungi (mucormycosis)
  • Haemorrhagic metastases
  • Granulomatosis with polyangiitis

Pearls

  • In a neutropenic patient the halo sign strongly suggests early invasive aspergillosis.
  • It is an early finding that may later evolve into the air crescent sign.

References

  • Radiopaedia: CT halo sign

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.