Asthma

Asthma
Brian C. Allen, MD
Tan-Lucien H. Mohammed, MD, FCCP
Key Facts
Terminology
  • Reactive airway disease
  • Intermittent reversible obstruction to air flow in lungs due to hyperreactivity and inflammation
Imaging Findings
  • Asthma typically involves mainly small and medium-sized bronchi
    • Air-trapping on expiratory scans most common finding
    • Bronchial wall thickening (50-90%)
    • Decreased lung attenuation (50%)
    • Mosaic lung attenuation
    • Degree of mosaic attenuation correlates with degree of asthma
  • HRCT useful to evaluate for bronchiectasis
  • Perform expiratory scans to visualize air-trapping
  • CXR: Limited role in diagnosis, important for complications of and processes that mimic asthma, alters treatment in few patients with acute asthma (5%)
Top Differential Diagnoses
  • Asthma Mimics
    • Airway Foreign Bodies
    • Cardiac asthma (edema of airway narrows lumen)
    • Recurrent Aspiration
    • Recurrent Pulmonary Embolus
    • Eosinophilic Pneumonia
    • Churg-Strauss Syndrome
    • Sarcoidosis
    • Bronchocentric Granulomatosis
    • Bronchiolitis Obliterans
    • Vocal cord dysfunction (factitious asthma)
Frontal radiograph shows a subtle diffuse increased reticular pattern in an asthmatic patient.
Axial HRCT shows a mosaic attenuation pattern consistent with air-trapping image.
TERMINOLOGY
Abbreviations and Synonyms
  • Reactive airway disease
Definitions
  • Intermittent reversible obstruction to air flow in lungs due to hyperreactivity and inflammation
  • Status asthmaticus: Medical emergency in which asthmatic attack is refractory to bronchodilator therapy
IMAGING FINDINGS
General Features
  • Best diagnostic clue
    • Air-trapping on expiratory scans
    • Bronchial wall thickening
  • Patient position/location
    • Segmental and distal bronchi
    • Nonuniform distribution through both lungs
CT Findings
  • More sensitive than chest radiography but not usually indicated
    • Used to assess for complications such as allergic bronchopulmonary aspergillosis, presence of emphysema in smokers, or to identify asthma mimics
  • Heterogeneous distribution of bronchial and lung parenchymal findings typical
  • Airways
    • Mainly small and medium-sized bronchi
    • Bronchial wall thickening (50-90%)
      • Degree of thickening correlates with severity of disease and airflow obstruction
      • Will improve with treatment
    • Bronchial artery ratio (normal approximately 1:1)
      • 75% of asthmatics (35% of bronchi) have bronchial artery ratio > 1 (but < 1.5)
    • Bronchial dilatation (30%)
      • Subsegmental bronchi larger than adjacent artery or nontapering airway morphology (typically cylindrical)
      • Bronchiectasis consider: APBA, irreversible airway remodeling, artifactual (from hypoxic vasoconstriction), or physiologic (from ventilation at large lung volumes)
    • Centrilobular micronodules or branching opacities (10-20%)
      • Finding most likely to be seen in patients with near-fatal asthma
  • Lung parenchyma
    • Decreased lung attenuation (50%)
    • Air-trapping (total volume > 1 segment) 50%
    • Mosaic lung attenuation
      • Degree of mosaic attenuation correlates with degree of asthma
    • Emphysema rare
      • Debatable whether secondary to asthma, usually only seen in those who smoke
Radiographic Findings
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Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Asthma

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