Histology and Explanation of Lobar pneumonia (leukocytic alveolitis)

Lobar pneumonia is an acute exudative inflammation of an entire pulmonary lobe, produced in 95 % of cases by Streptococcus pneumoniae (pneumococci).

If not treated, lobar pneumonia evolves in four stages :

* Congestion (first 2 days)
* Red hepatisation (fibrinous alveolitis) (2nd to 4th day)
* Grey hepatisation (leukocytic alveolitis) (4th to 8th day)
* Resolution (after 8th day)


Leukocytic alveolitis is the 3rd phase of the lobar pneumonia. Alveolar lumens are filled with leukocytic (suppurative) exudate (neutrophils and macrophages, in order to remove the fibrin). Alveolar walls are thickened due to capillary congestion and edema.