Pulmonary fibrosis is the preferred general term for the permanent replacement of lung parenchyma by connective tissue and is typically associated with functional impairment. A variety of insults cause focal or diffuse lung injury (mechanical, infectious, inflammatory and iatrogenic). Lung repair culminates in fibrosis with volume loss and architectural distortion. CT may also show traction bronchiectasis/bronchiolectasis and honeycombing 11.
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Terminology
The term should not be confused with idiopathic pulmonary fibrosis, which is a progressive fibrotic lung disease.
Pathology
Fibrosis in the lung is a process that occurs in the interstitium. Pulmonary fibrosis can be localized, segmental, or lobar or affect the entirety of the lung(s). Among the many conditions associated with pulmonary fibrosis are:
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significant acute insult to the lungs
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from a significant pulmonary infection
Post COVID fibrosis, especially in patients admitted to ICU and needing intubation/ventilation
diffuse alveolar damage from any source
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inhaled substances
coal/silica: progressive massive fibrosis
asbestos: asbestos-related pulmonary fibrosis
radiation: radiation-induced pulmonary fibrosis
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congenital conditions
autoimmune conditions
connective tissue disorders
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granulomatous conditions
sarcoidosis: pulmonary manifestations of sarcoidosis
tuberculosis: pulmonary manifestations of tuberculosis
granulomatosis with polyangiitis: pulmonary manifestations of granulomatosis with polyangiitis
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others
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chronic conditions
polymyalgia rheumatica (occasional case reports 6)
medications: drug-induced lung disease
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aging
some studies report thin-section CT findings associated with interstitial lung disease to some degree are frequently seen in "asymptomatic" elderly individuals 7,8
Radiographic features
CT
Many features can imply underlying pulmonary fibrosis, these include:
interlobular septal thickening: this feature is not specific for fibrosis