Radiographic Patterns and Causes of Ground Glass Opacities

Inflammatory and Infectious Processes

Various interstitial pneumonia patterns including organizing pneumonia (OP), diffuse alveolar damage (DAD), nonspecific interstitial pneumonia (NSIP), hypersensitivity pneumonitis (HP), and pulmonary eosinophilia can present as ground glass opacities (GGOs). 1, 2

Expansion of connective tissue space around conducting airways, accompanying vessels, and interlobular septa occurs in hydrostatic edema. 1
Radiographic findings of pulmonary edema include hazy opacities, Kerley lines, and sometimes a batwing appearance in hydrostatic edema. 2

Idiopathic pulmonary fibrosis (IPF) may show GGOs, though extensive ground glass opacity (>30% of lung involvement) should prompt consideration of diagnoses other than IPF. 4, 5, 6
Desquamative interstitial pneumonitis (DIP) typically presents with extensive GGOs. 5
Respiratory bronchiolitis-interstitial lung disease shows GGOs often with centrilobular nodules. 7
Nonspecific interstitial pneumonia (NSIP) frequently presents with GGOs without basal or peripheral predominance. 6

Drug-related pneumonitis from molecular targeting agents and immune checkpoint inhibitors can present as various interstitial pneumonia patterns with GGOs. 1
Radiation pneumonitis typically shows GGOs within the radiation portal or roughly within the area of high-dose radiation. 2
GGOs may appear 3-12 weeks after radiation exposure. 1

Alveolar hemorrhage can present with bilateral patchy GGOs in middle and lower lung zones. 2

When evaluating GGOs, clinicians should consider the distribution pattern (diffuse, patchy, peripheral, basal, etc.). 8
Associated findings such as reticular opacities, honeycombing, traction bronchiectasis, and centrilobular nodules are important to note when evaluating GGOs. 9, 10
When GGOs occur with reticular lines and traction bronchiectasis/bronchiolectasis, they indicate lung fibrosis. 4
Isolated GGOs without fibrotic features are usually associated with inflammatory cells in the alveolar septum or lumen (alveolitis). 4
The extent of GGOs on CT correlates with physiologic impairment and can help predict response to treatment. 6
GGOs may progress to reticular opacity or honeycombing on follow-up evaluation in fibrotic processes. 6
The "three-density pattern" (hypoattenuating, normal, and hyperattenuating lobules in close proximity) is highly specific for fibrotic hypersensitivity pneumonitis. 10