What do ground glass opacities on a chest computed tomography (CT) scan indicate?

Ground Glass Opacities on Chest CT: Clinical Significance and Differential Diagnosis

Ground glass opacities (GGOs) on chest CT scans indicate partial filling of air spaces or interstitial thickening of lung tissues that requires prompt clinical correlation to determine the underlying cause and appropriate treatment. 1

Definition and Characteristics

• GGOs are characterized by hazy increased lung attenuation with preservation of bronchial and vascular margins, distinguishing them from consolidation where bronchovascular structures are obscured 2
• They represent areas of increased density in the lungs while still allowing visualization of underlying vessels and bronchial walls 3

Pathophysiological Mechanisms

GGOs can result from several processes:

• Partial filling of air spaces
• Inflammatory or fibrotic interstitial thickening
• Increased capillary blood volume
• Interstitial or alveolar processes 2

Common Etiologies

GGOs are non-specific findings that can indicate various conditions:

Infectious Causes

• COVID-19 pneumonia (bilateral, peripheral, patchy GGOs) 3
• Pneumocystis pneumonia
• Cytomegalovirus pneumonia
• Influenza and other viral pneumonias 4

Non-infectious Inflammatory Conditions

• Hypersensitivity pneumonitis
• Drug-induced lung injury
• Cryptogenic organizing pneumonia (COP) 1
• Nonspecific interstitial pneumonia (NSIP)
• Acute interstitial pneumonia (AIP) 1

Vascular/Circulatory Causes

• Pulmonary edema
• Pulmonary hemorrhage
• Pulmonary infarction 4

Neoplastic Processes

• Early adenocarcinoma or adenocarcinoma in situ
• Lymphoma
• Metastatic disease 5

Other Causes

• Alveolar proteinosis
• Radiation pneumonitis
• Vaping-associated lung injury 4
• Asbestosis 1

Clinical Significance and Evaluation

Diagnostic Approach

1. Pattern and Distribution Assessment:

   • Peripheral vs. central
   • Focal vs. diffuse
   • Upper vs. lower lung predominance
   • Associated findings (nodules, reticulation, consolidation)

2. Clinical Correlation:

   • Acute vs. chronic presentation
   • Presence of fever, cough, dyspnea
   • Exposure history (occupational, medication, travel)
   • Immunocompromised status

3. Further Imaging Considerations:

   • High-resolution CT (HRCT) is the gold standard for detailed evaluation 1
   • Expiratory scans may help differentiate infiltrative processes from mosaic attenuation due to airway disease 2
   • Follow-up imaging to assess progression or resolution

Prognostic Implications

• GGOs may represent active and potentially treatable disease 6
• In idiopathic pulmonary fibrosis and other interstitial lung diseases, GGOs may indicate early, potentially reversible disease 1
• In the context of COVID-19, the extent of GGOs correlates with disease severity 3
• When associated with fibrosis, GGOs may indicate more advanced disease with poorer prognosis 1

Management Considerations

• Diagnosis often requires correlation with clinical data and sometimes lung biopsy
• Treatment targets the underlying cause
• Serial imaging is important to monitor disease progression or response to therapy
• In COVID-19, GGOs may persist for months after acute infection, with approximately 60% of patients showing abnormalities at 3 months 3
• In cases of suspected malignancy, persistent GGOs may warrant surgical intervention for definitive diagnosis 5

Common Pitfalls

• Physiologic dependent atelectasis can mimic GGOs, particularly in dependent lung regions
• Expiratory artifacts can create apparent GGOs
• Mosaic attenuation from vascular or airway disease can be mistaken for infiltrative GGOs 2, 7
• Overinterpretation of minimal or isolated GGOs without clinical correlation

Ground glass opacities represent an important radiological finding that warrants careful evaluation and appropriate clinical correlation to guide diagnosis and management decisions, with potential significant implications for patient morbidity and mortality.