What does scattered ground opacities in the right middle and bilateral lobes on a chest radiograph or computed tomography (CT) scan indicate?

Scattered Ground Glass Opacities in Right Middle and Bilateral Lobes: Interpretation and Clinical Significance

Scattered ground glass opacities (GGOs) in the right middle and bilateral lobes represent areas of increased lung density where vessels and bronchial walls remain visible, and may indicate various pathological processes including infection, inflammation, early interstitial lung disease, drug-related pneumonitis, or pulmonary edema. 1, 2

Definition and Radiographic Characteristics

• Ground glass opacity (GGO) appears as a diffuse homogeneous increase in lung density on high-resolution computed tomography (HRCT), where vessels and bronchial walls remain visible 2
• GGOs represent partial filling of airspaces, thickening of the interstitium, partial collapse of alveoli, increased capillary blood volume, or a combination of these factors 1
• When evaluating GGOs, it's important to note their distribution pattern (diffuse, patchy, peripheral, basal) and associated findings such as reticular opacities or traction bronchiectasis 1

Common Causes of Scattered Ground Glass Opacities

Inflammatory and Infectious Processes

• Various interstitial pneumonia patterns including organizing pneumonia (OP), diffuse alveolar damage (DAD), and nonspecific interstitial pneumonia (NSIP) can present with GGOs 3, 1
• Infectious etiologies such as viral pneumonia, Pneumocystis pneumonia, and mycobacterial infections commonly present with GGOs 2

Drug-Related Pneumonitis

• Drug-related pneumonitis from molecular targeting agents and immune checkpoint inhibitors can present with various interstitial pneumonia patterns with GGOs 3
• Multiple CT patterns can be seen with drug-related pneumonitis, including NSIP, organizing pneumonia (OP), hypersensitivity pneumonitis (HP), and simple pulmonary eosinophilia 3

Interstitial Lung Diseases

• Early interstitial lung disease may present with scattered GGOs before progression to more fibrotic changes 3, 1
• Nonspecific interstitial pneumonia (NSIP) frequently presents with GGOs without basal or peripheral predominance 2
• Hypersensitivity pneumonitis can show poorly defined small centrilobular nodules and bilateral GGOs 3, 1

Other Causes

• Pulmonary edema can present with hazy opacities and may have a dependent distribution 1, 2
• Alveolar hemorrhage can present with bilateral patchy GGOs in middle and lower lung zones 1

Clinical Significance and Approach

• The extent of GGOs on CT correlates with physiologic impairment and can help predict response to treatment 2
• When GGOs occur with reticular lines and traction bronchiectasis/bronchiolectasis, they indicate lung fibrosis 2
• Isolated GGOs without fibrotic features are usually associated with inflammatory cells in the alveolar septum or lumen (alveolitis) 2

Diagnostic Approach

• Determine if GGOs are associated with other radiographic findings, such as reticular abnormalities, traction bronchiectasis, or honeycombing, which suggest fibrotic process 4
• Consider specific patterns that suggest particular diagnoses:
  • Peripheral or peribronchovascular distribution may suggest organizing pneumonia pattern 4
  • "Three-density pattern" (hypoattenuating, normal, and hyperattenuating lobules in close proximity) is highly specific for fibrotic hypersensitivity pneumonitis 1
• Evaluate for potential drug exposures, as many medications can cause drug-related pneumonitis with GGO patterns 3
• Consider clinical context including duration of symptoms, smoking history, and occupational exposures 5

Management Recommendations

• Follow-up chest CT scan is typically recommended to monitor for progression or resolution of GGOs 4
• For interstitial lung abnormalities (ILAs), follow-up imaging in 2-3 years is often appropriate 4
• If drug-related pneumonitis is suspected, consider discontinuation of the offending agent 3
• Dependent GGOs should be confirmed with prone imaging to rule out atelectasis 4

Clinical Pitfalls and Caveats

• GGOs in dependent lung regions on supine imaging may represent atelectasis rather than true pathology 4
• Subtle GGOs may represent early disease that could progress if not appropriately managed, highlighting the importance of follow-up 4
• The diagnosis of drug-related pneumonitis is based on a combination of clinical, radiologic, and sometimes histologic findings in a patient who has received a drug known or suspected to cause the abnormalities 3