From the Guidelines
Ground glass opacities (GGOs) are most commonly caused by infections, such as COVID-19, as well as interstitial lung diseases, pulmonary edema, and malignancies, with the specific cause often determined by the pattern and distribution of the opacities on imaging, as well as clinical context and associated findings. The causes of GGOs can be broadly categorized into infectious, inflammatory, and neoplastic etiologies. Infectious causes include viral pneumonias like COVID-19, influenza, and cytomegalovirus, as reported by Yoon et al. 1. Inflammatory causes encompass interstitial lung diseases such as idiopathic pulmonary fibrosis, hypersensitivity pneumonitis, and sarcoidosis, as discussed in the American Thoracic Society guidelines 1. Neoplastic causes include malignancies like adenocarcinoma and lymphoma. Other causes of GGOs include drug-induced lung injury, radiation pneumonitis, and autoimmune conditions like rheumatoid arthritis and systemic lupus erythematosus.
Some key points to consider in the diagnosis of GGOs include:
- The pattern and distribution of the opacities on imaging, with peripheral distribution suggesting COVID-19 and upper lobe predominance indicating hypersensitivity pneumonitis 1
- Clinical context, including symptoms, exposure history, and timing of onset, as emphasized in the management of immune-related adverse events in patients treated with immune checkpoint inhibitor therapy 1
- The role of transbronchial biopsy in assisting to rule out other etiologies like lymphangitic spread of tumor or infection, as discussed in the context of ICPi pneumonitis 1
- The treatment of patients with symptomatic ICPi pneumonitis with corticosteroids as an initial treatment, based on several studies that report clinical improvement in > 80% of cases 1
In terms of specific imaging findings, GGOs appear as hazy areas of increased lung opacity that do not obscure underlying bronchial structures or vascular margins, unlike consolidation. The presence of ground glass opacity on CT often regresses on treatment in patients who have histologic desquamative interstitial pneumonitis (DIP), but may not decrease as readily in those with histologic usual interstitial pneumonia (UIP) 1. An area of ground glass opacity may progress to reticular opacity or honeycombing on follow-up evaluation 1.
Overall, the diagnosis and management of GGOs require a comprehensive approach that takes into account the patient's clinical presentation, imaging findings, and associated conditions, as well as the potential for underlying malignancy or other serious conditions. The most recent and highest quality study, as reported by De Simone et al. 1, highlights the importance of chest CT examination in the initial diagnosis and evaluation of the severity of COVID-19 pneumonia, which is a common cause of GGOs.
From the Research
Causes of Ground Glass Opacities
- Ground glass opacities (GGOs) are characterized by areas of hazy increased attenuation of the lung with preservation of bronchial and vascular margins 2
- GGOs can correlate with several pathogenic processes, such as partial filling of air spaces, inflammatory or fibrotic interstitial thickening, and increased capillary blood volume 2
- Infiltrative GGO can represent either interstitial or alveolar processes, and can be caused by a variety of pulmonary processes, including infections, inflammation, and fibrosis 2, 3
- COVID-19 pneumonia has been linked to the development of interstitial lung disease and pulmonary fibrosis, with some patients displaying fibrotic-like patterns on chest computed tomography shortly after infection 4, 5, 6
- The severity of acute COVID-19 disease has been linked to an increased risk of residual imaging and functional abnormalities, including pulmonary fibrosis 4, 6
- Risk factors for pulmonary fibrosis post-COVID-19 include increased erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and lactate dehydrogenase (LDH), as well as the duration of hospitalization and the severity of pneumonia 6