DefinitionParapneumonic pleural effusion is a buildup of fluid between layers of the tissue lining the lung and the chest cavity, which develops in the setting of pneumonia.Reviewed ByReview Date: 08/13/2010David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.