Imaging of Interstitial Lung Diseases (ILDs) and HRCT Approach

Jul 1, 2024

Interstitial Lung Diseases (ILDs) and HRCT Approach

Introduction and Review

  • Previous Lecture Recap
    • Overview of normal anatomy and structures in a scan
    • Planes and lymph node anatomy
  • Today's Focus
    • General approach to HRCT using pattern approach
    • Specific topic: Imaging of Interstitial Lung Diseases (ILDs)

Key Concepts

  • Secondary Pulmonary Lobule
    • Smallest functional unit in thoracic imaging
    • Importance radiologically for pathologies
    • Contains centrilobular artery and respiratory bronchiole
    • Typical size: 1 to 2 cm
    • The smallest unit for all diseases
  • Interlobular Structures
    • Connective tissue, lymphatics, and veins
    • Pathologies can involve different parts: centrilobular interstitium, interlobular septa, intralobular septa, peribronchovascular bundles

Patterns in HRCT

  • Centrilobular Pattern
    • Nodule in the center of pulmonary lobule
    • Does not touch pleural surface
    • Differential diagnoses (DDx): Hypersensitivity pneumonitis, bronchitis (including infectious bronchitis, follicular bronchitis), TB
  • Interstitial Involvement
    • Interlobular septal thickening or intralobular septal thickening
    • Common causes: pulmonary edema, lymphatic diseases (e.g., sarcoidosis, silicosis, lymphangitic carcinomatosis)

Diagnosing ILDs

  • Role of CT Scans in Identifying Patterns
    • Ensure proper scan type: inspiratory vs. expiratory
    • Expiratory Scans
      • Can mislead if reported wrongly as ILDs
      • Key identifier: collapsed posterior wall of trachea
      • Not the right type for diagnosing ILDs
      • Used to identify air trapping
  • Inspiratory Scans
    • Preferred method for HRCT
    • Ensuring the scan is well-performed for accurate diagnosis
    • Avoid misdiagnosis by checking scan quality

Reporting HRCT Scans

  • Window Selection
    • Do not report ILDs on lung window
    • Use high-resolution CT reconstruction (HRCT Recon)
    • Sharp window kernels required
    • Recon can be done from the acquisition console
  • Other Practical Tips
    • When identifying ILDs, everything must be done accurately to avoid false positives
    • ILDs diagnosis should be precise with attention to specific patterns

Summary

  • ILDs diagnosis can be complex and unique to each patient
    • Recognizing different patterns and their clinical correlations is crucial
    • Proper technique and understanding of lung anatomy aids in better diagnosis of ILDs in HRCT