How are the stages of inflammatory response in lobar pneumonia characterized?

Updated: Sep 30, 2020
  • Author: Justina Gamache, MD; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Four stages of inflammatory response are classically described, as follows:

  1. Congestion: This stage is characterized by vascular engorgement, intra-alveolar fluid, and numerous bacteria. The lung is heavy, boggy, and red.

  2. Red hepatization: In this stage, massive confluent exudation develops, with red blood cells, leukocytes, and fibrin filling the alveolar spaces. The affected area appears red, firm, and airless, with a liver-like consistency.

  3. Gray hepatization: This stage is characterized by progressive disintegration of red blood cells and the persistence of a fibrin exudate.

  4. Resolution: The consolidated exudate within the alveolar spaces undergoes progressive enzymatic digestion to produce debris that is later resorbed, ingested by macrophages, coughed up, or becomes organized by fibroblasts.

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