Fibrotic idiopathic interstitial pneumonia: high-resolution computed tomography considerations.

The fibrotic idiopathic interstitial pneumonias comprise usual interstitial pneumonia (UIP) and nonspecific interstitial pneumonia (NSIP). The characteristic high-resolution computed tomography findings of UIP are reticular abnormality and honeycombing with basal and peripheral predominance. Honeycombing is the strongest predictor of UIP. The extent of fibrosis on computed tomography (CT) is an important prognostic indicator in idiopathic pulmonary fibrosis (IPF). When ground-glass attenuation is seen in IPF it commonly progresses to fibrosis and honeycombing. Imaging may help to detect complications of IPF, including accelerated progression, lung cancer, and secondary infection. Our understanding of the clinical and radiological features of NSIP is still evolving. The CT finding of extensive ground-glass abnormality and some reticular abnormality, with basal and peripheral predominance, is strongly suggestive of NSIP. However, the CT appearances of NSIP overlap with those of UIP, organizing pneumonia (OP), and desquamative interstitial pneumonia (DIP), and biopsy may be necessary to sort this out. Other idiopathic pneumonias that may be associated with CT evidence of lung fibrosis include DIP, OP, acute interstitial pneumonia, and lymphoid interstitial pneumonia.