fibrotic bronchiolitis

8/3/2019 Fibrotic Bronchiolitis

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Constrictive Bronchiolitis (Bronchiolitis Obliterans) Postinfectious Bronchiolitis Toxic Fume Exposure Transplant- related Bronchiolitis Cryptogenic Bronchiolitis Obliterans

Bronchiolitis Obliterans with OrganizingPneumonia


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Defined histologically as concentricluminalnarrowing of the membranous and respiratorybronchiolessecondary to submucosal andperibronchiolar inflammation andfibrosis without

any intraluminal granulation tissue or polyps Can be cryptogenic; postinfectious, orsecondary

to noxious fume inhalation, graft-versus-hostdisease,lung transplantation, rheumatoid

arthritis, inflammatory boweldisease, andpenicillamine therapy; histologyvaries accordingto the cause.


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Direct CT signs ofbronchiolitis are usually absentbecause the amountof abnormal soft tissue inand around the bronchioles is relativelysmall

Characteristics: Mosaic attenuation Bronchial dilation

Air trapping - can be lobular, segmental, or lobar orpresent as larger areasof confluent decreased lungattenuation that are accentuatedon expiratory imaging(expiratory high- resolution CT)

Areas of low attenuation - reduction in the size of thepulmonary vessels


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Most cases of aresecondary to an infection withadenovirus type 7 during childhoodor infancy May also developwith measles, pertussis,

tuberculosis, and Mycoplasmainfection.

Alveolar maturation occurs in children by the age of 8years.If bronchiolitis occurs before this age, it affectsthe divisionof alveoli, with a resultant decrease in thenumber of alveoliand pulmonary vessels.

Patchy distribution ofbronchiolitis and airtrapping(mosaic attenuation)

Focal areas of decreased lung opacity withsharpmargins, reduced-size pulmonary vessels, bronchialwallthickening, and bronchiectasis


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35-year-old manwith cellularbronchiolitissecondaryto Mycoplasmainfect

ion. Multiple poorly

defined centrilobularnodules, many ofwhich connect to

branching linearstructures (arrows),tree-in-bud pattern.


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Reactive airways dysfunction syndrome appearsto be more commonthan bronchiolitis as asequel of toxic fume exposure andis usually notassociated with any CT manifestations.

Silo filler's

lung is a classic cause ofconstrictive bronchiolitis, althoughits incidencemay have decreased with aggressivecorticosteroidtreatment

Work-related inhalation of flavoring agents

(usedin making popcorn) has been found toresult in a clinical presentationand imagingpattern typical of constrictive bronchiolitis.


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Constrictivebronchiolitispattern in a patientwho had severe

obstructive lungdisease

Shows diffusedecrease in lung

attenuation, withmild cylindricbronchiectasis.


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Constrictive bronchiolitis remains the mostcommon form of chronic rejectionin patientswith lung transplants, occurring in up to 50% ofpatients.

The diagnosisof bronchiolitis obliterans

syndrome in these patients is basedon reductionin the forced expiratory flow volume in 1sec(FEV1)to less than 80% of the posttransplantationbaseline value

Riskfactors: acute rejection lymphocytic bronchiolitis medication noncompliance cytomegalovirus infection


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CT findings bronchial dilation bronchial wall thickening mosaicperfusion air trapping on expiratory images (most sensitive

indicator) The bronchial dilation found in patients with

posttransplantation bronchiolitisobliteransusually has lower lung predominance.

Constrictive bronchiolitis is seen as amanifestation of graft-versus-host disease

in10% of people who have received allogeneic bonemarrow transplants. CT findings are the samewith bronchiolitis obliterans.


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Constrictivebronchiolitis pattern in41-year-old maledouble lung transplantrecipient with

bronchiolitis obliteranssyndrome. Shows bilateral diffuse

cylindricbronchiectasis, withdiffuse decrease invascularity, anddecrease in lungattenuation


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Uncommon entity thatis most common in olderwomen; characterized by airwayobstruction thatprogresses to respiratory failure

Imaging findingssimilarto those of patients with

other forms of constrictive bronchiolitismosaicattenuation, air trapping, and cylindrical

bronchiectasis


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Must be differentiatedfrom refractory asthma. A mosaic pattern oflung attenuation was the most reliable

distinguishing feature, being found in one (3%) of 30 patients withasthma and in seven(50%) of 14 patientswith bronchiolitis obliterans.

Distinction between bronchiolitis obliterans

and panlobularemphysema

recognition ofparenchymal destruction, vascular distortion, andlinear scars orthickened septa at the lung bases in most patientswith panlobular emphysema

Neuroendocrine hyperplasia, a rare entity, can cause apatternof mosaic attenuation identical to thatof bronchiolitis obliterans,but it is usually associated withsmall scattered pulmonary nodules.


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Constrictivebronchiolitispattern in patientwith pulmonaryneuroendocrine cellhyperplasia.

Shows mosaic

attenuation, whichis more marked onright than on left.


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Anidiopathic interstitial pneumonia(cryptogenic organizing pneumonia)ratherthan a small airways disease because itsradiologic,clinical, and physiologic features

are more similar to thoseof a restrictiveparenchymal process than a small airwaysdisease.


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Bronchiolitis may be classified into inflammatory andfibroticsubtypes Direct signs of bronchiolitis includecentrilobularnodules and tree-in-bud pattern Indirect signs include mosaicattenuation and airtrapping High-resolution CT findings correlatewith the

histology of different forms of bronchiolitis.

Classic examples of eachentity exist, but there can

be substantial overlap in the appearances,

anddistinguishing among these entities is not alwayspossible. Clinical details willusually help to narrowthe differential diagnosis.


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