Is the Lateral Decubitus Radiograph Necessary for the Management of a Parapneumonic Pleural Effusion?

Abstract

A pproximately 50% of patients who are admitted to the hospital with community-acquired pneumonia will develop a pleural effusion.1,2 While most parapneumonic effusions will resolve without specific therapy, approximately 10% will become complicated or progress to empyema.3 Because delays in the drainage of these clinically significant effusions have been associated with increased morbidity and mortality,4 prompt detection and accurate characterization of a parapneumonic effusion are important. Guidelines5 based on a consensus conference have comprehensively summarized the literature regarding parapneumonic effusions and have made specific recommendations for their management. Although this document reflects the “state of the art,” as the authors noted, most studies of parapneumonic effusions have been observational, often with a limited numbers of patients. One of the recommendations in the guidelines was that all patients with a parapneumonic effusion should have a chest radiograph performed with a lateral decubitus view.5 This recommendation also was incorporated into the American Thoracic Society guidelines6 for the care of adults with communityacquired pneumonia. The rationale is that if the thickness of the effusion on the lateral decubitus view is 1 cm, the effusion is small enough so that no further intervention is needed.1 While there is good evidence that small effusions resolve without specific therapy,1 the suggestion that a lateral decubitus radiograph is required to determine the appropriate course of action with respect to a parapneumonic effusion appears to have been made without sufficient supporting data. The purpose of this article is to review the indications and usage of the lateral decubitus chest radiograph and demonstrate its limited value in the setting of parapneumonic pleural effusions. Radiographs of the chest made with the patient in the standard erect position usually will not reveal the presence of a pleural effusion 300 to 500 mL in size, as the fluid usually pools in the posterior costophrenic sulcus.7,8 The varying volumes reported may be due to differences in patient size, as a larger individual probably can “hide” a larger volume of fluid than can a smaller individual. The lateral decubitus view was first described by Merlo Gomez and Heidenreich,9 in 1924, as a technique to identify the presence of small pleural effusions. Its first English-language description was by Rigler,7 in 1931, who used this technique to confirm the presence of pleural effusions in a small series of patients despite the absence of a visible effusion using the standard erect views. Subsequently, other investigators demonstrated that the sensitivity of this view can be increased by placing a pillow under the patient’s pelvis, so that the thorax slopes downward away from the lung base.10 By injecting known amounts of fluid into cadavers, in 1973 Moskowitz et al8 demonstrated that effusions as small as 5 to 10 mL could be detected using the lateral decubitus view.