Usual interstitial pneumonia (UIP) pattern on high-resolution CT shows honeycombing with basal, subpleural, bilateral distribution. On histology, the hallmark finding that distinguishes UIP from NSIP is:
- A Temporal heterogeneity: new fibroblastic foci adjacent to old dense fibrosis ✓
- B Temporal uniformity: all fibrotic areas are the same age (old fibrosis only)
- C Diffuse lymphocytic alveolitis with preserved alveolar architecture
- D Granuloma formation within alveolar walls without caseation
Explanation
The hallmark of UIP (the histological pattern of IPF) is temporal and spatial heterogeneity: active fibroblastic foci (pale, myxoid zones of active fibrosis representing recent injury) are found directly adjacent to dense, old, collagenous fibrosis and honeycombing, all within the same biopsy. This mixture of ages of fibrosis indicates ongoing, repetitive epithelial injury. NSIP shows temporal uniformity (all fibrosis is the same age) and often a cellular background; it has a better prognosis. Diffuse lymphocytic alveolitis is more characteristic of cellular NSIP. Granulomas point to hypersensitivity pneumonitis or sarcoidosis.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.