Uncategorized

  • Etymology

    Derived from “interstitial,” referring to the connective tissue framework of the lungs, and “abnormalities,” indicating deviations from normal structure or function.

    AKA and abbreviation

    Interstitial lung abnormalities (ILAs).

    What is it?

    Interstitial lung abnormalities (ILAs) are incidental radiologic findings on CT scans that represent subtle changes in the lung interstitium. These findings may reflect:

    1. Repair from prior injury, such as inflammation, infection, or exposure-related damage.
    2. Early interstitial lung disease (ILD), which may progress to fibrosis.

    ILAs are not associated with significant respiratory symptoms at the time of diagnosis and do not meet the criteria for established ILD.

    Characterized by

    Radiologic findings of ILAs, in order from most to least common:

    1. Subpleural fibrosis: Thickening and fibrosis predominantly in the peripheral and subpleural regions.
    2. Ground-glass opacities: Diffuse hazy opacities that do not obscure underlying vascular structures.
    3. Reticular changes: Fine linear opacities forming a network-like pattern, often basal or subpleural.
    4. Bronchiolectasis: Dilated small airways caused by retraction or fibrosis in surrounding lung tissue.
    5. Traction bronchiectasis: Larger airway dilation caused by fibrotic retraction and architectural changes.
    6. Architectural distortion: Displacement or distortion of normal anatomic structures, including fissures, vessels, and bronchi.
    7. Arcade fibrosis: Fibrosis along bronchovascular bundles or arcades, commonly seen in early fibrotic diseases.
    8. Honeycombing: Cystic air spaces indicative of advanced fibrosis or progressive ILD.

    Caused by

    • Most common cause: Age-related or idiopathic changes.
    • Other causes include:
      • Infection: Subclinical viral or bacterial infections.
      • Inflammation/Immune: Early connective tissue diseases (e.g., rheumatoid arthritis, scleroderma).
      • Neoplasm: Early lymphangitic carcinomatosis (rare).
      • Mechanical Trauma: Post-radiation or surgical changes.
      • Metabolic: Pulmonary alveolar proteinosis, amyloidosis.
      • Circulatory: Pulmonary venous congestion due to heart failure.
      • Inherited/Congenital: Genetic predispositions, such as telomerase-related mutations.
      • Other: Environmental exposures (e.g., smoking, asbestosis, or silica exposure).

    Resulting in:

    • Progressive structural and functional changes in the lungs in some cases, leading to early symptoms of ILD or pulmonary fibrosis.
    • In other cases, ILAs remain stable and asymptomatic.

    Structural changes:

    • Thickening of interstitial compartments, including interlobular septa and alveolar walls.
    • Fibrosis of the subpleural and arcade regions.
    • Development of bronchiolectasis, traction bronchiectasis, and early architectural distortion.

    Pathophysiology:

    • Inflammation, injury, or genetic predisposition leads to remodeling and deposition of extracellular matrix proteins, resulting in interstitial thickening.
    • Chronic processes may progress to traction bronchiectasis, subpleural fibrosis, and honeycombing.

    Pathology:

    Histopathologic findings include early fibroblast foci, patchy interstitial thickening, and mild inflammatory infiltration in some cases.

    Diagnosis:

    • ILAs are incidental findings on chest CT scans performed for other reasons (e.g., cancer screening or trauma evaluation).
    • Symptoms are typically absent or minimal at the time of discovery.

    Clinical:

    • Symptoms: Typically asymptomatic but may progress to dyspnea or cough in advancing cases.
    • Signs: Rarely detected clinically; crackles may appear in progressive cases.

    Radiology:

    • CXR:
      • Often normal; subtle findings may include faint reticular patterns or subpleural thickening.
    • CT (High-Resolution CT):
      • Subpleural fibrosis and reticular changes.
      • Ground-glass opacities and early honeycombing in fibrotic cases.
      • Bronchiolectasis and traction bronchiectasis due to fibrotic retraction.
      • Architectural distortion, particularly in subpleural and basal regions.
    • Associated Findings:
      • Coexisting emphysema or nodules in smokers.
      • Arcade fibrosis along bronchovascular bundles.

    Labs:

    • Autoimmune markers: Evaluate for early connective tissue diseases.
    • Genetic testing: For familial or inherited predispositions (e.g., telomerase mutations).

    Management:

    • Observation: Regular follow-up imaging to monitor progression.
    • Lifestyle interventions: Smoking cessation and environmental exposure reduction.
    • Specialist referral: Pulmonology evaluation if ILAs progress or symptoms develop.
    • Treatment: Targeted therapy for underlying conditions (e.g., antifibrotics, immunosuppressants).

    Radiology Detail:

    • CXR:
      • Findings: Subtle or absent findings; occasionally reticular changes or subpleural thickening.
      • Associated Findings: Coexisting emphysema in smokers.
    • CT:
      • Parts: Interlobular septa, alveolar walls, bronchovascular bundles, subpleural regions.
      • Size: Segmental, subsegmental, or lobar involvement.
      • Shape: Reticular, nodular, or ground-glass opacities.
      • Position: Basal and subpleural predominance.
      • Character: Subtle fibrosis and architectural distortion.
      • Time: Stable or slowly progressive.
      • Associated Findings: Traction bronchiectasis, bronchiolectasis, and honeycombing.
    • Other relevant Imaging Modalities:
      • MRI: Rarely used; findings are nonspecific.
      • PET-CT: May show mild metabolic activity in inflammation or neoplasm.

    Pulmonary function tests (PFTs):

    • Often normal initially.
    • May reveal early restrictive changes in progressive cases.

    Recommendations:

    • Regular monitoring: Repeat CT imaging in 6?12 months to assess progression.
    • Multidisciplinary approach: Coordinate care with radiology, pulmonology, and rheumatology when needed.
    • Early intervention: Treat contributing factors such as smoking or autoimmune diseases.

    Key Points and Pearls:

    • ILAs represent subtle interstitial changes and can be a precursor to ILD or reflect prior lung injury.
    • Subpleural fibrosis, reticular changes, and ground-glass opacities are hallmark findings.
    • High-resolution CT is essential for accurate characterization.
    • Early architectural distortion, traction bronchiectasis, and bronchiolectasis are signs of progression.
    • Careful follow-up is needed to prevent progression to advanced fibrotic disease.