Histopathology and Pathogenesis

Although the features of NSIP can be sharply defined, the real-life separation of NSIP from other IIPs, particularly UIP/IPF, remains difficult. The histopathology of NSIP incorporates a broad spectrum of features with varied degrees of alveolar wall inflammation (cellular NSIP) versus paucicellular fibrosis (fibrotic NSIP) (Table 1) (8,12). Furthermore, it is not uncommon to identify small foci of honeycomb change, rare collection of fibroblastic foci, and 

Mild-to-moderate interstitial chronic inflammation Type II pneumocyte hyperplasia in areas of inflammation 

Dense or loose interstitial fibrosis lacking temporal heterogeneity and/or patchy 

Lung architecture appears lost on H E stains but is relatively preserved on 

Mild or moderate chronic inflammation Pertinent negative findings  

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