Histologic changes: At the center of an acinus is a respiratory bronchiole that contains some loose granulation tissue (proliferative bronchiolitis) (arrow). The surrounding interstitium, including the periarterial tissue (A=artery), is infiltrated with a mixture of lymphocytes and plasma cells. PMNs and eosinophils are rare. There is mild type II cell hyperplasia. Alveoli contain increased numbers of macrophages and lymphocytes.


Within the acinus, small veins (arrows indicate the wall of one vein) are infiltrated and narrowed by lymphocytes and plasma cells. This infiltrate does not constitute a destructive angiitis because the elastic layers of the vessel are preserved, as an elastic tissue stain would show. Note the alveolitis (widened alveolar walls, interstitial lymphoid infiltrate, type II cell hyperplasia, and increased alveolar cells) in the surrounding alveoli.


Clinical summary Image 3

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