1. The Histopathology of IPF
UIP is the histologic lesion essential for IPF diagnosis
Cardinal features
Temporal heterogeneity
Dense fibrosisnormal lung
Predilection for peripheral (subpleural) and basilar region
Fibroblastic foci (aggregates of proliferating fibroblasts and myofibroblasts)
Microscopic honeycomb cysts
The Histopathology of IPF
The ATS/ERS committee defines UIP as the histologic abnormality that is essential for a diagnosis of IPF. The histologic hallmark and chief diagnostic criterion is a temporally heterogeneous appearance with alternating areas of normal lung, inflammation, dense fibrosis, and honeycombing. Temporal heterogeneity refers to the fact that areas of chronic honeycombing, subacute interstitial fibrotic tissue, and acute alveolar epithelial necrosis are often located directly adjacent to areas of normal lung, are present at the same time. These histological patterns predominantly affect the peripheral and basilar regions of the lungs. The fibrotic zones are composed of dense collagen, with scattered fibroblastic foci. The temporal heterogeneity showing normal lung, active fibrosis, and end-stage honeycombing suggests that UIP may not be an early lesion, but rather an intermediate or end-stage lesion.
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