pulmonary disorders
Pleural Effusion
Diagnosis of Pleural Effusion
Chest x-ray Thoracic ultrasonography Pleural fluid analysis Sometimes CT with venous contrast, CT angiography, or other tests Pleural effusion is suspected in patients with pleuritic pain, unexplained dyspnea, or suggestive signs. Diagnostic tests are indicated to document the presence of pleural fluid and to determine its cause (see figure). Chest x-ray is the first test done to confirm the presence of pleural fluid. The lateral upright chest x-ray should be examined when a pleural effusion is suspected. In an upright x-ray, 75 mL of fluid blunts the posterior costophrenic angle. Blunting of the lateral costophrenic angle usually requires about 175 mL but may take as much as 500 mL. Larger pleural effusions opacify portions of the hemithorax and may cause mediastinal shift; effusions>4 L may cause complete opacification of the hemithorax and mediastinal shift to the contralateral side. Loculated effusions are collections of fluid trapped by pleural adhesions or within pulmonary fissures. Further imaging (lateral decubitus x-rays, chest CT, or ultrasonography) should be done if it is unclear whether an x-ray density represents fluid or parenchymal infiltrates or whether suspected fluid is loculated or free-flowing; these tests are more sensitive than upright x-rays and can detect small fluid volumes. Loculated effusions, particularly those in the horizontal or oblique fissure, can be confused with a solid pulmonary mass (pseudotumor). They may change shape and size with changes in the patient’s position and amount of pleural fluid. Thoracic ultrasonography is considered standard of care for diagnosis of pleural effusion and is done at the bedside by pulmonologists, or sometimes emergency physicians, avoiding the need for radiologist review. It is highly accurate for the detection of small volumes of pleural fluid and provides additional diagnostic information (eg, the presence of septation, pleural thickening). CT with venous contrast is a valuable next investigation that provides information on pleural enhancement and potential pleural nodularity. CT with venous contrast is valuable for evaluating the underlying lung parenchyma for infiltrates or masses when the lung is obscured by the effusion or when the detail on chest x-rays is insufficient for distinguishing loculated fluid from a solid mass. How To Do Thoracentesis None Thoracentesis should be done using ultrasonographic guidance in all cases because it increases procedure accuracy and prevents complications. Despite common practice, chest x-ray need not be repeated after thoracentesis unless patients develop symptoms suggesting pneumothorax (dyspnea or chest pain) or unless the clinician suspects that air may have entered the pleural space during the procedure. Pleural fluid analysisis done to diagnose the cause of pleural effusion. Analysis begins with visual inspection, which can Distinguish bloody and chylous (or chyliform) from other effusions Identify purulent effusions strongly suggestive of empyema Identify viscous fluid, which is characteristic of some mesotheliomas Fluid should always be sent for total protein, glucose, lactate dehydrogenase (LDH), cell count and cell differential, and Gram stain. Other tests such as pleural fluid pH, aerobic and anaerobic bacterial cultures, cytology, tuberculosis fluid markers [adenosinedeaminase or interferon-gamma], amylase, mycobacterial and fungal stains and cultures, triglycerides, and cholesterol are used in appropriate clinical settings. Fluid analysis helps distinguish transudates from exudates; multiple criteria exist, but not one perfectly discriminates between the 2 types. When Light’s criteria are used (see table), serum LDH and total protein levels should be measured as close as possible to the time of thoracentesis for comparison with those in pleural fluid. Light’s criteria correctly identify almost all exudates but misidentify about 20% of transudates as exudates. If transudative effusion is suspected (eg, due to heart failure or cirrhosis) and none of the biochemical measurements are<15% above the cutoff levels for Light’s criteria, the difference between serum and the pleural fluid protein is measured. If the difference is>3.1 g/dL (> 31 g/L), the patient probably has a transudative effusion. Imagingmay also help. If the diagnosis remains unclear after pleural fluid analysis, CT with venous contrast enhancement is indicated to assess for pleural enhancement, pleural nodularity, pulmonary infiltrates, or mediastinal lesions. CT pulmonary angiography is indicated to rule out suspected pulmonary embolus. Findings of pulmonary emboli indicate the need for long-term anticoagulation. Pleural nodularity and thickening indicate the need for pleural biopsy (thoracoscopic or image guided). The presence of lung infiltrates or lesions, depending on suspected causes, may indicate the need for bronchoscopy or image-guided lung biopsy. deaminase in the pleural fluid is measured. A level > 40 U/L (667 nkat/L) has a 95% sensitivity and specificity for the diagnosis of tuberculous pleuritis ( Diagnosis reference ); however, the * Based on presence of fever, weight loss, history of cancer, or other suggestive symptoms. TB = tuberculosis. 1.Roberts ME, Rahman NM, Maskell NA, et al. British Thoracic Society Guideline for pleural disease.Thorax2023;78(Suppl 3):s1-s42. doi:10.1136/thorax-2022-219784 