Asbestosis



Asbestosis


Helen T. Winer-Muram, MD










Axial HRCT shows bilateral subpleural curvilinear opacities image in a patient with mild asbestosis. Subpleural lines persist on prone images (not shown).






Axial HRCT in the same patient shows peripheral ground-glass opacities image and septal lines image. Note the diaphragmatic plaques image.


TERMINOLOGY


Definitions



  • Asbestosis: Interstitial lung disease due to inhalation of asbestos fibers


IMAGING FINDINGS


General Features



  • Best diagnostic clue: Basilar interstitial fibrosis and pleural plaques


  • Patient position/location: Posterobasilar subpleural lung


  • Morphology: Fibrosis centered on respiratory bronchioles


CT Findings



  • Morphology



    • Reticular (linear opacities) most common manifestation



      • Short intralobular or interlobular septal thickening


    • Centrilobular nodules or branching opacities earliest manifestation



      • Reflects fibrosis around small airways where fibers located


    • Subpleural curvilinear lines



      • Parallel chest wall within 1 cm of the pleura, length 5-10 cm


      • Represent peribronchial confluent fibrosis or atelectasis associated with obstructed respiratory bronchioles


      • Not specific for asbestosis


    • Parenchymal bands project perpendicular from pleura



      • 2-5 cm long


      • Fibrosis along interlobular septa or bronchovascular bundles


    • Small airways obstruction (from fibrosis incited by asbestos fibers)



      • May result in mosaic perfusion pattern


      • Traction bronchiolectasis is uncommon (more common in idiopathic pulmonary fibrosis)


    • Fibrosis with traction bronchiectasis and honeycombing in advanced disease



    • Pleural plaques (80%), best finding to differentiate from idiopathic pulmonary fibrosis


  • Distribution



    • Peripheral basilar lung most common distribution



      • Reflects initial location of deposited fibers


      • Because fibers are too large to be removed by macrophages, fibers tend to reflect initial deposition


Radiographic Findings



  • Radiography



    • May be normal (10-20%); pleural plaques (25%)


    • International Labor Office (ILO) classification compared to standard radiographs “B” reading



      • Asbestosis generally s, t, or u opacities


    • Late: End-stage honeycombing; progressive massive fibrosis extremely rare


    • Lung cancer: Lower zone predominance in contrast to upper zone predominance in general population of smokers


Imaging Recommendations



  • Best imaging tool



    • CT useful to differentiate lung nodules from pleural plaques, round atelectasis, and lung fibrosis



      • 10% of asbestos-exposed workers screened by CT for asbestosis will have lung mass


    • Screening asbestos-exposed workers



      • Of those with clinical asbestosis: Chest radiographs abnormal in 80%; HRCT abnormal in 96%


      • 33% with neither clinical nor chest radiographic evidence of asbestosis abnormal at HRCT


      • However, false-negatives for early asbestosis (25%)


  • Protocol advice: Prone scans help to differentiate true interstitial lung disease from gravity-related physiology


DIFFERENTIAL DIAGNOSIS


Idiopathic Pulmonary Fibrosis



  • No pleural plaques


  • Ground-glass opacities and traction bronchiolectasis are more common


  • Band-like opacities and mosaic pattern of perfusion are less common


Scleroderma



  • No plaques; however, pleural thickening and pseudoplaques are common


  • Dilated esophagus


Rheumatoid Arthritis



  • No plaques; arthritis and joint erosions


Hypersensitivity Pneumonitis



  • No plaques


  • Less severe in costophrenic angles, more severe in mid and upper lungs


  • Mosaic perfusion from air-trapping, more common


Cytotoxic Drug Reaction



  • No plaques; interstitial thickening similar


  • Prototypical drug: Methotrexate


Lymphangitic Tumor



  • No plaques but pleural effusion and lymphadenopathy are common


  • Asymmetric distribution


  • Nodular thickening of septa and core bronchovascular structures


PATHOLOGY


General Features



  • General path comments



    • Asbestos mineral properties: Heat resistant, high tensile strength, flexible, durable



      • 2 types of fibers: Serpentine and amphibole


    • Serpentine (chrysotile or white asbestos, 90% commercial asbestos)



      • Curly, wavy fiber, long (> 100 µm), diameter (20-40 µm)


    • Amphibole




      • Crocidolite (blue asbestos), amosite (brown asbestos), anthophyllite, tremolite, actinolite


      • Straight rigid fiber; length:width = 3:1 is aspect ratio


    • Retention: Long thin fibers > short thick fibers


    • Asbestos (ferruginous) bodies



      • Hemosiderin-coated fiber (mostly amphibole)


      • Incompletely phagocytized by macrophages


      • Not pathognomonic for asbestosis


      • Coated fibers fewer than uncoated fibers


      • Not correlated with fibrosis


    • Pathophysiology



      • Increased deposition of fibers in lower lung zones due to gravitational ventilatory gradient


      • Fibers deposit in respiratory bronchioles


      • No lymphatic removal, largest and most harmful asbestos fibers too large to be removed by macrophages


  • Epidemiology

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Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Asbestosis
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