Of the idiopathic interstitial pneumonias, the differentiation between idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonitis (NSIP) raises considerable diagnostic challenges, as their clinical presentations share many overlapping features. IPF is a fibrosing pneumonia of unknown cause, showing a histologic pattern of usual interstitial pneumonia (UIP), and has a poorer prognosis than does NSIP. This review examines whether the radiographic features of IFP and NSIP as assessed by high-resolution computed tomography (HRCT) can be used to distinguish between these two entities.
The diagnostic accuracy of HRCT for UIP and NSIP has been reported to be approximately 70% in various studies. Disagreement between the HRCT diagnosis and the histologic diagnosis occurs in approximately one-third of the cases. The predominant feature of honeycombing on HRCT yields a specificity of approximately 95% and sensitivity of approximately 40% for UIP. In contrast, a predominant feature of ground glass opacities (GGOs) gives a sensitivity of approximately 95% and specificity of approximately 40% for NSIP.
The finding of honeycombing as the predominant HRCT feature suggests the diagnosis of UIP and may exclude the need for biopsy. Predominant features of GGOs are not specific enough to distinguish between NSIP and UIP.