In panacinar (panlobular) emphysema, which part of the acinus is primarily and earliest affected?

• A Respiratory bronchioles (proximal acinus)
• B Alveolar ducts and alveolar sacs (distal acinus) with uniform involvement of entire acinus ✓
• C Alveolar walls adjacent to fibrous septa (paraseptal)
• D Central acinus around respiratory bronchioles with sparing of distal alveoli

Explanation

Panacinar (panlobular) emphysema involves uniform destruction of the entire acinus from respiratory bronchioles through alveolar ducts to alveolar sacs, without predilection for any particular part. It is typically associated with alpha-1 antitrypsin deficiency and is predominantly lower-lobe. This contrasts with centriacinar (centrilobular) emphysema (primarily affects respiratory bronchioles, most common in smokers, upper-lobe predominant). Paraseptal emphysema affects alveoli adjacent to pleura and fibrous septa.

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

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