Idiopathic pulmonary fibrosis (IPF) is associated with which histological pattern that is mandatory for diagnosis in the absence of a confident radiologic UIP pattern?

• A Non-specific interstitial pneumonia (NSIP) — temporal homogeneity with ground-glass and fibrosis
• B Desquamative interstitial pneumonia (DIP) — diffuse macrophage filling of alveoli
• C Usual interstitial pneumonia (UIP) — temporal and spatial heterogeneity with honeycombing and fibroblastic foci ✓
• D Organizing pneumonia (OP) — intraluminal plugs of granulation tissue (Masson bodies)

Explanation

IPF is pathologically defined by the UIP pattern, which shows temporal heterogeneity (areas of normal lung adjacent to areas of fibrosis and honeycombing), spatial heterogeneity (subpleural and basal predominance), and characteristic fibroblastic foci (active zones of fibrogenesis). Honeycombing with microscopic honeycombs of enlarged cystic spaces lined by bronchiolar epithelium is the hallmark. NSIP shows temporal homogeneity and is more common in connective tissue disease-associated ILD. DIP and OP are separate entities.

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

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Written and medically reviewed by the StethoPrep medical team.