Ground-glass opacification

Last revised by Rohit Sharma on 3 Apr 2024

Ground-glass opacification/opacity (GGO) is a descriptive term referring to an area of increased attenuation in the lung on computed tomography (CT) with preserved bronchial and vascular markings. It is a non-specific sign with a wide etiology including infection, chronic interstitial disease and acute alveolar disease.

Ground glass opacification is also used in chest radiography to refer to a region of hazy lung radiopacity, often fairly diffuse, in which the edges of the pulmonary vessels may be difficult to appreciate 7.

The use of the term ground glass derives from the industrial technique in glassmaking whereby the surface of normal glass is roughened by grinding it.

Ground-glass opacities have a broad etiology:

  • normal expiration

  • partial filling of air spaces

  • partial collapse of alveoli

  • interstitial thickening

  • inflammation

  • edema

  • hemorrhage

  • fibrosis

  • lepidic proliferation of neoplasm

Broadly speaking, the differential for ground-glass opacification can be split into 5:

  • infectious processes (opportunistic vs non-opportunistic)

  • chronic interstitial diseases

  • acute alveolar diseases

  • other causes

To narrow down the differential diagnosis, following points may be of help 8:

Is the GGO pathological?

  • if the membranous posterior wall of the trachea bows anteriorly, the scan has been performed in expiration and lung attenuation will be increased.

  • dependent atelectasis is a common normal finding. If the extent is greater than normal, prone imaging can differentiate normal from abnormal

  • if mosaic attenuation pattern is present, attenuation measurements help to distinguish normal from abnormal

What is the time course of the GGO?

  • acute GGO lasts only days or weeks. In this setting, imaging is less important as the most common causes of acute GGO (infection, edema, hemorrhage, ARDS, and non-fibrotic hypersensitivity pneumonitis) may have overlapping and non-specific features. The clinical features are the key to diagnosis

  • chronic GGO may remain relatively unchanged for many weeks and even years. In these case the spatial distribution and additional imaging findings are important

  • recurring GGO (e.g., hemorrhages in vasculitis), is a potential pitfall when assessing the time course

  • recent bronchoalveolar lavage may alter the attenuation in both directions (i.e., increasing attenuation through remaining fluid, and decreasing attenuation after treating pulmonary alveolar proteinosis)

What is the spatial distribution?

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