A patient with IPF (idiopathic pulmonary fibrosis) has a surgical lung biopsy showing usual interstitial pneumonia (UIP) pattern. The characteristic 'temporal and spatial heterogeneity' of UIP refers to:

• A Uniform fibrosis throughout all lung lobes simultaneously
• B Patchy fibrosis with honeycombing at the periphery alternating with normal lung, with fibroblastic foci at the active border ✓
• C Diffuse alveolar damage with hyaline membranes alternating with organizing pneumonia
• D Geographic necrosis surrounded by neutrophilic inflammation in different stages

Explanation

The UIP pattern is defined by temporal heterogeneity (areas of old fibrosis/honeycombing coexist with active fibroblastic foci at the junction with normal lung) and spatial heterogeneity (patchy distribution — more severe subpleurally and basally with sparing of the central/apical lung). Fibroblastic foci (clusters of proliferating fibroblasts/myofibroblasts at the advancing fibrotic front) are the hallmark active lesion. This pattern distinguishes UIP/IPF from NSIP (diffuse homogeneous fibrosis/GGO without honeycombing) and COP (organizing pneumonia with preserved lung architecture).

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

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Written and medically reviewed by the StethoPrep medical team.