Cytologic Changes of Pleural Effusion in Pulmonary Embolism

To the Editor.—  We read with interest the paper by Drs Bynum and Wilson on "Characteristics of Pulmonary Effusions Associated With Pulmonary Embolism."¹ We agree with their conclusion that cytologic changes in pulmonary embolism are variable and not diagnostic. However, we believe that their cytologic findings in the effusions secondary to pulmonary embolism need further clarification.We have studied the pleural effusions from 16 patients with pulmonary embolism and found that the cytologic findings vary in cellular pattern and cellular morphologic structure with time from the acute insult. Within several days after the acute insult, the pleural effusion may be bloody and contain many neutrophils and basophilic mesothelial cells, some of which may be bizarre in their morphology. With resolution of the process, the neutrophils decrease and the lymphocytes and mesothelial cells increase. The mesothelial cells aggregate in sheets and often undergo degeneration. The degenerating mesothelial cell demonstrates a