What is the workup for ground glass infiltration on a chest high-resolution computed tomography (HRCT) scan?

Workup for Ground Glass Infiltration on Chest HRCT

The comprehensive workup for ground glass infiltration on HRCT should include clinical evaluation, pulmonary function testing, laboratory studies, and in some cases, lung biopsy to determine the underlying cause, as ground glass opacities represent a nonspecific finding that can indicate various pathologies ranging from inflammation to early fibrosis.

Understanding Ground Glass Opacities (GGO)

• Ground glass opacity refers to a diffuse homogeneous increase in lung density on HRCT where vessels and bronchial walls remain visible 1, 2
• When GGO occurs with reticular lines and traction bronchiectasis/bronchiolectasis, it indicates lung fibrosis 1, 3
• Isolated GGO without fibrotic features usually suggests inflammatory cells in the alveolar septum or alveolar lumen (alveolitis) 1
• GGO may progress to reticular opacity or honeycombing on follow-up evaluation in fibrotic processes 1, 3

Initial Clinical Assessment

• Evaluate duration of symptoms (acute vs. chronic) to narrow differential diagnosis 4
• Assess for exposure history (occupational, environmental, bird exposure) which is crucial for diagnosing conditions like hypersensitivity pneumonitis 1
• Document smoking history, as this affects the differential diagnosis and may be associated with respiratory bronchiolitis-interstitial lung disease 3
• Review medication history for potential drug-induced pneumonitis 3

HRCT Pattern Analysis

• Determine distribution pattern of GGO (diffuse, patchy, peripheral, basal) 3:

  • Peripheral and basal predominance suggests IPF 1
  • Diffuse distribution without basal predominance may indicate NSIP or hypersensitivity pneumonitis 1, 3
  • Patchy distribution may suggest organizing pneumonia 3

• Identify associated radiographic features 1:

  • Reticular abnormalities and honeycombing suggest fibrotic disease 1
  • Centrilobular nodules with GGO suggest hypersensitivity pneumonitis 1
  • Mosaic attenuation and air-trapping strongly suggest hypersensitivity pneumonitis 1
  • "Three-density pattern" (hypoattenuating, normal, and hyperattenuating lobules in close proximity) is highly specific for fibrotic hypersensitivity pneumonitis 3

Pulmonary Function Testing

• Perform complete pulmonary function tests including 1:

  • Spirometry to assess for restrictive pattern (reduced vital capacity with preserved FEV1/FVC ratio)
  • Lung volumes by body plethysmography (reduced TLC)
  • Diffusing capacity (DLCO), which is often reduced and may precede abnormalities in lung volume
  • Arterial blood gases to assess for hypoxemia

• Exercise testing may reveal 1:

  • Increased minute ventilation primarily through increased respiratory frequency
  • Elevated VD/VT ratio (may indicate pulmonary vascular disease)

Laboratory Studies

• Complete blood count to assess for systemic inflammation 5
• Specific serologies based on clinical suspicion:
  • Antinuclear antibodies, rheumatoid factor, and other autoimmune markers for connective tissue diseases 1
  • Precipitating antibodies for suspected hypersensitivity pneumonitis 1
  • Infectious disease workup if infection is suspected 3

Additional Diagnostic Procedures

• Bronchoalveolar lavage (BAL) to evaluate cellular profile:

  • Lymphocytosis suggests hypersensitivity pneumonitis or sarcoidosis
  • Neutrophilia may indicate infection or acute inflammation
  • Eosinophilia suggests eosinophilic pneumonia

• Consider lung biopsy when diagnosis remains uncertain after non-invasive testing 1:

  • Surgical lung biopsy provides the most definitive tissue diagnosis
  • Transbronchial biopsy may be sufficient for certain conditions like sarcoidosis

Follow-up Imaging

• Serial HRCT is valuable to assess disease progression or response to therapy 1
• Side-by-side comparison of baseline and follow-up HRCT is strongly recommended to accurately assess changes 1
• Increased extent of GGO on follow-up may indicate disease progression 1
• Regression of GGO with treatment may occur in conditions like DIP 1

Common Pitfalls and Caveats

• Extensive GGO (>30% of lung involvement) should prompt consideration of diagnoses other than IPF 1
• Normal HRCT does not exclude early infiltrative lung disease, as the parenchymal infiltration may be too slight to cause CT abnormality 1
• Partial volume effects of bronchovascular bundles and chest wall can mimic GGO 6
• Motion artifacts can lead to misinterpretation of GGO 6
• GGO in patients with emphysema may be associated with increased systemic inflammation and emphysema progression 5

Multidisciplinary Approach

• Integration of clinical, radiological, and when available, pathological findings is essential for accurate diagnosis 1
• Expert chest radiologist interpretation significantly improves diagnostic accuracy 1
• The accuracy of a confident diagnosis made on HRCT by a trained observer is about 90% for conditions like IPF 1