In usual interstitial pneumonia (UIP), the histological hallmark distinguishing it from other interstitial lung diseases is:

• A Uniform distribution of alveolar damage throughout both lungs
• B Dense lymphocytic infiltration with germinal centers in the interstitium
• C Temporal and spatial heterogeneity with fibroblast foci alongside normal lung and honeycombing ✓
• D Organizing pneumonia pattern with intraluminal fibroblastic plugs

Explanation

UIP (the histological pattern underlying IPF) is characterized by temporal and spatial heterogeneity: areas of dense fibrosis and honeycombing (old lesions) coexist with fibroblastic foci (active lesions) and relatively normal lung in the same biopsy. This 'patchwork' pattern with subpleural/basal predominance is pathognomonic. NSIP shows uniform temporal homogeneity. Lymphoid aggregates suggest NSIP or hypersensitivity pneumonitis. Organizing pneumonia pattern is COP.

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

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Written and medically reviewed by the StethoPrep medical team.