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Bird’s nest sign (lungs)

Last revised by Dr Himanshu Mishra on 15 Jul 2021

The bird’s nest sign refers to the appearance created by a reverse halo sign with associated irregular and intersecting areas of stranding or irregular lines within the area of ground-glass opacity 1.

Both bird's nest sign and reverse halo signs are suggestive of invasive pulmonary fungal infection (e.g., angioinvasive aspergillus or mucormycosis) in susceptible patient populations 1-4.

Differential diagnosis

The reverse halo and bird’s nest signs are not specific for invasive fungal disease and may also be seen in other conditions, including 1:

Mucormycosis vs aspergillosis

It is important to distinguish mucormycosis from aspergillosis because the treatments can differ (voriconazole is not effective against mucormycosis), and because appropriate early treatment of mucormycosis may improve the outcome.

Imaging features that favor mucormycosis over aspergillus infection in a neutropenic patient are 1-4:

It is to be noted that there has been a rise of mucormycosis in the second wave of the COVID-19 pandemic in India attributed to uncontrolled diabetes and overzealous use of steroids.

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Cases and figures

  • Pulmonary mucormycosis complicating COVID-19 pneumonia
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