Bronchiolitis, Constrictive



Bronchiolitis, Constrictive


Melissa L. Rosado-de-Christenson, MD, FACR





Key Facts


Terminology



  • Concentric peribronchiolar fibrosis of membranous and respiratory bronchioles


Imaging Findings



  • Radiography



    • Normal chest radiographs


    • Hyperinflation


  • CT/HRCT



    • Mosaic pulmonary attenuation


    • Air-trapping on expiratory CT/HRCT


    • Low attenuation; air-trapping and reflex vasoconstriction


    • High attenuation; redistribution of blood flow to relatively normal lung


    • Bronchial dilatation, bronchiectasis, bronchial wall thickening


Top Differential Diagnoses



  • Panlobular Emphysema


  • Pulmonary Hypertension


  • Asthma


Pathology



  • Etiologies



    • Postinfectious


    • Post-transplantation


    • Collagen vascular disease


    • Inhalational injury


  • Nonuniform bronchiolocentric fibrosis


Clinical Issues



  • Progressive dyspnea, cough


Diagnostic Checklist



  • Expiratory HRCT for detection of air-trapping







Axial HRCT shows mosaic attenuation and areas of decreased lung attenuation image containing small vessels that alternate with areas of higher lung attenuation image and contain normal-sized pulmonary vessels.






Axial HRCT shows the typical findings of constrictive bronchiolitis, including mosaic attenuation, bronchiectasis image, and bronchial wall thickening. Note the subtle middle lobe centrilobular nodules image.


TERMINOLOGY


Abbreviations and Synonyms



  • Bronchiolitis obliterans syndrome (BOS)


Definitions



  • Bronchiolitis = broad spectrum of inflammatory and fibrotic changes centered on small conducting airways


  • Confusing and often inconsistent terminology



    • Bronchiolitis obliterans refers to both constrictive bronchiolitis and bronchiolitis obliterans organizing pneumonia


    • Obliterative bronchiolitis refers to clinical syndrome of airflow obstruction associated with HRCT findings of air-trapping


    • Various classification schemes



      • Classification based on etiology and clinical syndromes


      • Classification based on histologic features


  • Constrictive bronchiolitis = peribronchiolar fibrosis with resultant bronchiolar narrowing or obstruction



    • No fibroblastic proliferation


    • Collagen deposition extrinsic to airway lumen


    • Diffuse patchy involvement


    • Irreversible process


  • Swyer-James-MacLeod syndrome = unilateral or focal postinfectious constrictive bronchiolitis


  • BOS = post-transplantation airflow obstruction



    • Clinical diagnosis; decrease in FEV1 from baseline


    • Potential BOS (BOS 0-p) = decrease in forced expiratory flow in mid expiratory phase &/or milder decrease in FEV1


  • Bronchiolitis obliterans organizing pneumonia or cryptogenic organizing pneumonia



    • Cellular bronchiolitis with fibroblastic proliferation


    • Process confined to airway lumen


    • Often localized


    • Resolution with treatment


IMAGING FINDINGS


General Features



  • Best diagnostic clue: Lobular mosaic attenuation accentuated by expiratory imaging


CT Findings



  • Minimum intensity projection (MinIP)




    • Projects lowest attenuation voxels on every view through volume onto 2D image


    • Optimal visualization of diffuse lung disease, airways, and ground-glass opacity


  • Maximum intensity projection (MIP)



    • Projects highest attenuation voxels on every view throughout volume onto 2D image


    • Optimal visualization of nodules and vessels


  • Mosaic attenuation on inspiratory CT/HRCT



    • Heterogeneous lung attenuation


    • Alternating ↓ and ↑ lung attenuation



      • Reflects nonuniform bronchiolar obliteration


    • Hyperlucent underventilated (air-trapping) and underperfused lung (hypoxic vasoconstriction)


  • Normal or near normal inspiratory CT/HRCT



    • Mosaic attenuation may only be visible on expiratory imaging


  • Diffuse decreased lung attenuation in severe disease



    • May be subtle


  • Air-trapping on expiratory HRCT



    • Geographic areas of decreased lung attenuation



      • Decreased vessel caliber from hypoxic vasoconstriction


      • No decrease in volume of affected lung


    • Areas of increased (normal) lung attenuation



      • Increased vessel caliber and blood flow


      • Decrease in volume


      • Well- or poorly defined margins


    • May be seen in patients without any disease



      • Typically smokers and elderly individuals


      • Frequent in lower lobe superior segments and inferior lingula


      • Involves < 25% of CT cross-sectional area


      • Lobular air-trapping of < 3 adjacent secondary lobules in 50% of asymptomatic patients


  • Associated findings



    • Proximal bronchial dilatation, bronchiectasis, bronchial wall thickening



      • Common in post-transplantation and postinfectious constrictive bronchiolitis


    • Scant centrilobular nodules


    • Pulmonary nodules & mosaic attenuation



      • Consider diffuse idiopathic neuroendocrine cell hyperplasia


    • Predisposed to pneumothoraces, pneumomediastinum


  • Swyer-James-MacLeod syndrome



    • Focal lung hyperlucency and decreased vascularity


    • Normal or decreased volume of affected lung


    • Air-trapping in affected lung on expiratory CT/HRCT


    • Areas of decreased attenuation and air-trapping of other lobes or contralateral lung


Radiographic Findings



  • Radiography



    • Normal chest radiograph


    • Nonspecific findings



      • Hyperinflation


      • Peripheral attenuation of vascular markings


    • Swyer-James-MacLeod syndrome



      • Unilateral hyperlucent lung


      • Decreased pulmonary vascularity


      • Normal or decreased volume of affected lung


      • Small ipsilateral hilum


      • Air-trapping on expiratory radiography


MR Findings



  • Hyperpolarized 3-helium MR imaging; more sensitive than HRCT for detection of air-trapping

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

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