Usual interstitial pneumonia (UIP) on CT shows bilateral basal-predominant honeycombing with traction bronchiectasis. On histology, the key distinguishing feature from other interstitial pneumonias is:

• A Uniform alveolar filling by macrophages
• B Diffuse alveolar damage with hyaline membranes
• C Temporal heterogeneity — fibrosis of varying ages with fibroblastic foci ✓
• D Eosinophilic infiltration with Charcot-Leyden crystals

Explanation

The hallmark of UIP (the histologic pattern of IPF) is temporal and spatial heterogeneity: areas of established dense fibrosis (old) alternating with fibroblastic foci (active areas of ongoing fibrosis, new) and relatively normal lung — all in the same biopsy. This 'patchwork' pattern distinguishes UIP from NSIP (uniform, temporally homogeneous fibrosis) and DIP (uniform macrophage filling).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.