Usual interstitial pneumonia (UIP) is the histological pattern underlying idiopathic pulmonary fibrosis. The hallmark histological feature that distinguishes UIP from other interstitial pneumonias is:
- A Uniform temporal pattern of alveolar damage with hyaline membranes throughout both lungs
- B Diffuse alveolar infiltration by eosinophils with peripheral blood eosinophilia
- C Heterogeneous temporal pattern — areas of normal lung, interstitial inflammation, fibrosis, and honeycombing — with fibroblastic foci at the advancing edge ✓
- D Granulomatous inflammation around small bronchioles with lymphocytic bronchiolitis
Correct answer: C. Heterogeneous temporal pattern — areas of normal lung, interstitial inflammation, fibrosis, and honeycombing — with fibroblastic foci at the advancing edge
Explanation
UIP has a characteristic 'temporally heterogeneous' pattern: areas of old dense fibrosis with honeycombing (basal/subpleural) exist adjacent to areas of less affected lung and active fibroblastic foci (myofibroblast proliferation). This heterogeneity (varying stages of injury in the same biopsy) distinguishes UIP from NSIP (uniform inflammation/fibrosis) or DAD (uniform hyaline membranes).
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.