Interstitial Infiltrate on Chest XRay

Aka: Interstitial Infiltrate on Chest XRay, Interstitial Infiltrate, Interstitial Marking, Pulmonary Infiltrate, Reticular Interstitial Infiltrate, Honeycomb Interstitial Infiltrate, Nodular Interstitial Infiltrate, Linear Interstitial Infiltrate, Kerley Lines, Kerley A Lines, Kerley B Lines, Kerley's Lines

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II. Pathophysiology

  1. Interstitial Infiltrates occur within the connective tissue surrounding the air spaces
  2. Lung interstitial space is only visible in disease state (highlighted by fluid, fibrosis or tumor)
  3. Pulmonary vessels are still visible but with fuzzy margins ("trees in fog")
  4. Contrast with Alveolar Infiltrates which occur within the air spaces (Bronchioles, alveoli) and obscure the vessels
  5. Interstitial Infiltrates may be linear (e.g. Kerley B Lines), reticular (web-like) or nodular

III. Approach

  1. Distinguish Interstitial Infiltrate pattern from Alveolar Infiltrate pattern to identify primary process
  2. Findings more suggestive of interstial infiltrate (contrasted with Alveolar Infiltrate)
    1. Diffuse infiltrate
    2. Follow distribution of pulmonary vessels
    3. Lung base appears more radiodense than apex

IV. Types: Linear Interstitial Infiltrates (Kerley A and B Lines)

  1. General: Interlobular thickened septae or congested Lymphatics
    1. Pulmonary Edema (most common, e.g. Left Congestive Heart Failure)
    2. Mitral Stenosis
    3. Lymphangitic carcinoma
    4. Lymphoma
    5. Mycoplasma pneumonia or Viral Pneumonia
    6. Sarcoidosis
    7. Idiopathic Pulmonary Fibrosis
    8. Hemosiderosis (late findings)
  2. Kerley A Lines
    1. Long (2-6 cm), linear upper lobe white lines radiating out from the hilum (central lung)
    2. Oriented perpendicular to pleura
  3. Kerley B Lines
    1. Short (1-2 cm) linear horizontal white lines in periphery, perpendicular to the pleura
    2. Lines are of water density in the interlobular septa and are always in contact with pleura
    3. Occur near costophrenic angles of lower lobes
    4. Causes
      1. Pulmonary Edema (e.g. Congestive Heart Failure)
      2. Lymphatic carcinomatosis

V. Types: Reticular Interstitial Infiltrate

  1. Spider web network of lines anywhere in lung
  2. Overlapping short linear and curved white lines
  3. Irregular distribution (may be patchy or diffuse) and typically bilateral
  4. Typically caused by reversible Interstitial Lung Disease
    1. Viral Pneumonia
    2. Mycoplasma pneumonia
    3. Sarcoidosis
    4. Hypersensitivity pneumonitis

VI. Types: Peripheral Reticular Interstitial Infiltrate (honeycomb)

  1. Honeycomb appearance in the peripheral lung spaces (bibasilar and lateral lung, sparing the perihilar and apical regions)
  2. Honeycombs represent patchwork of lines surrounding small cystic lung spaces
  3. Typically caused by advanced, irreversible Interstitial Lung Disease
    1. Interstitial Pneumonia
    2. Fibrosing alveolitis
    3. Asbestosis

VII. Types: Nodular Interstitial Infiltrate

  1. Discrete, round small, similarly sized densities (<1 cm)
  2. Localized to upper and middle lobes (typically spares the lower lobes)
  3. Causes
    1. Sarcoidosis
    2. Langerhan Cell Histiocytosis
    3. Silicosis
    4. Coal Worker's Lung
    5. Miliary Tuberculosis
      1. Numerous pellet sized white Nodules (Miliary pattern)

VIII. Types: Reticulo-Nodular Interstitial Infiltrate

  1. Combination of both the reticular and nodular patterns

IX. References

  1. Collins and Stern (2008) Chest Radiology, Lippincott Williams Wilkins, Philadelphia, p. 34-5
  2. Ouellette and Tetreault (2015) Clinical Radiology, Medmaster, Miami, p. 4-25

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