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.
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Terminology
Fibrosis may be focal and may be stable over time. In others, fibrosis can be progressive and follow a recognisable CT pattern such as UIP or NSIP. Interstitial lung abnormality refers to early fibrotic lung disease which may progress.
Pathology
Fibrosis in the lung is a process that occurs in the interstitium. Pulmonary fibrosis can be localised, 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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ageing
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
Early pulmonary fibrosis 12:
irregular interlobular septal thickening
irregular pleural thickening
intralobular reticular opacity
This can progress with increasing reticulation and:
traction bronchiectasis and bronchiolectasis
Treatment and prognosis
Antifibrotic medication provides benefit for patients with progressive pulmonary fibrosis 12.