In usual interstitial pneumonia (UIP) — the histological pattern underlying idiopathic pulmonary fibrosis (IPF) — which feature is most characteristic and diagnostic?

• A Uniform interstitial inflammation without honeycombing
• B Temporal and spatial heterogeneity with fibroblastic foci adjacent to honeycombing ✓
• C Diffuse alveolar damage pattern with hyaline membranes
• D Granulomatous interstitial inflammation without fibrosis

Explanation

The hallmark of UIP pattern (seen in IPF) is temporal and spatial heterogeneity — areas of normal lung alternating with areas of old dense fibrosis (honeycombing) and areas of active fibrosis (fibroblastic foci/myofibroblast clusters at the advancing edge). This 'patchwork' pattern at low power distinguishes UIP from NSIP (uniform temporality), DIP (diffuse macrophage accumulation), or organizing pneumonia. Fibroblastic foci are particularly characteristic of UIP.

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

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Written and medically reviewed by the StethoPrep medical team.