Ground-glass opacity

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High-resolution CT: increase in density in areas of ground glass and air trapping in lower lobes in patients with hypersensitivity pneumonitis.

In radiology, ground glass opacity (GGO) is a nonspecific finding on computed tomography (CT) scans that indicates a partial filling of air spaces in the lungs by exudate or transudate, as well as interstitial thickening or partial collapse of lung alveoli.

Differential diagnosis[edit]

The differential diagnosis of the many causes of GGO includes pulmonary edema, infections (including cytomegalovirus and Pneumocystis jirovecii pneumonia), various noninfectious interstitial lung diseases (such as hypersensitivity pneumonitis, Hamman-Rich syndrome), diffuse alveolar hemorrhage, and cryptogenic organizing pneumonia.[1]

Reversed halo sign[edit]

Reversed halo sign.

A reversed halo sign is a central ground-glass opacity surrounded by denser consolidation. Criteria include that the consolidation should form more than three-fourths of a circle and be at least 2 mm thick.[2] It is suggestive of bronchiolitis obliterans organizing pneumonia (BOOP),[3] but is only seen in about 20% of individuals with this condition.[2] It can also be present in infectious diseases such as paracoccidioidomycosis, tuberculosis, zygomycosis, and aspergillosis, as well as in granulomatosis with polyangiitis, lymphomatoid granulomatosis, and sarcoidosis.[4]


  1. ^ Jannette Collins, MD; Eric J. Stern, MD (1998). "Ground glass opacity on CT scanning of the chest: What does it mean?" (PDF). Applied Radiology. Retrieved 2012-02-01. 
  2. ^ a b Radswiki; et al. "Reversed halo sign (lungs)". Radiopaedia. Retrieved 2018-01-02. 
  3. ^ Brett M. Elicker, W. Richard Webb (2012). Fundamentals of High-Resolution Lung CT: Common Findings, Common Patterns, Common Diseases, and Differential Diagnosis. Lippincott Williams & Wilkins. ISBN 9781469824796. 
  4. ^ Page 256 in: D Karthikeyan (2013). High Resolution Computed Tomography of the Lungs: A Practical Guide. JP Medical Ltd. ISBN 9789350904084. 

External links[edit]