In usual interstitial pneumonia (UIP), the histological hallmark that distinguishes it from other interstitial pneumonias is:

• A Uniform temporal pattern of inflammation and fibrosis throughout all lung zones
• B Diffuse organizing pneumonia pattern with intraluminal fibroblastic plugs
• C Hyaline membranes lining alveolar ducts
• D Temporally heterogeneous fibrosis with alternating areas of dense fibrosis, fibroblastic foci, and normal lung (honeycombing) ✓

Explanation

UIP (the histological correlate of idiopathic pulmonary fibrosis) is characterised by temporal heterogeneity — different areas of lung show different stages of fibrosis in the same section. Dense collagenous fibrosis, fibroblastic foci (active fibrosis), honeycombing (subpleural), and preserved normal parenchyma coexist. This 'patchwork' pattern differs from the uniform temporal homogeneity of NSIP. UIP has the worst prognosis among the interstitial pneumonias.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.