Pulmonary nodule CT

Pulmonary Nodule Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Halo Sign

• The halo sign refers to a zone of ground-glass attenuation surrounding a pulmonary nodule or mass on CT images.
• The presence of a halo of ground-glass opacity or ground-glass attenuation is usually associated with hemorrhagic nodules.
• In severely neutropenic patients, the halo sign is highly suggestive of infection by an angioinvasive fungus, most commonly Aspergillus.
• Vascular invasion by this fungus results in thrombosis of small- to medium-sized vessels, which causes ischemic necrosis.
• At pathologic examination, the nodules represent foci of infarction, and the halo of ground-glass attenuation results from alveolar hemorrhage.
• Although it is less common, the halo sign may also be observed in nonhemorrhagic nodules, in which case either tumor cells or inflammatory infiltrate account for the halo of ground-glass attenuation.