Identification of Comorbid Conditions on HRCT

Patients with IPF are at high risk for having emphysema,¹¹ which carries a significantly poorer outcome than IPF alone.⁵ Emphysema and pulmonary fibrosis have opposing physiologic effects, often leading to apparent conserved lung function during pulmonary function tests.¹² Therefore, recognition of coexistent fibrosis and emphysema on HRCT is of utmost importance as physiologic testing rarely diagnoses both disorders.¹²

Emphysema is characterized by permanently enlarged airspaces with destruction of alveolar walls.⁷ On HRCT, emphysema appears as focal areas of low attenuation, often without visible walls.⁷ Centrilobular emphysema has a nonuniform, centrilobular distribution predominantly localized to the upper lung.⁷ Paraseptal emphysema is subpleural and peribronchovascular, interspersed with areas of intact interlobular septa.⁷ Bullae may also be present on HRCT scans of patients with paraseptal emphysema.⁷ In patients with emphysema and fibrosis, fibrotic changes are often lower-lung predominant, while emphysema is often upper-lung predominant, spatially distinguishing the features.