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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