The pathologic findings in rickettsial pneumonia.

A fatal case of Q fever pneumonia with demonstration of the organisms in the lungs is presented. The disease clinically simulates bacterial lobar pneumonia. Neutrophils were conspicuously absent in the inflammatory process. Histiocytes predominated in the alveolar septal spaces and produced both radiologically and pathologically an alevolar infiltrate. Histiocytic hyperplasia and focal necrosis were present. Histiocytes similar to those seen in the alveolar spaces of the lungs distorted the normal architecture of the lymph nodes. In scattered areas necrosis with histiocytes palisading in the periphery simulating the lesions of cat-scratch disease and tularemia were seen.