Symptoms of pleural effusions are nonspecic and include cough, dyspnea, pleuritic chest pain, fever, night sweats, and/or weight loss if secondary to malignancy. Physical exam ndings include decreased breath sounds on ausculta­tion, dullness to percussion, and decreased tactile fremitus if a large volume is present, typically at least 300mL [16]. Chest radiographs are typically the initial diagnostic imaging exam performed when a pleural effusion is suspected. On a PA chest radiograph, 175mL of pleural uid must be present to blunt the lateral costophrenic angles; 75mL is necessary to blunt the posterior costophrenic angle, while a decubitus view can detect as little as 10mL of pleural uid (Fig.42.4) [7, 9, 11]. CT can detect very small volumes of uid and, as with ascites, can aid in identifying the underlying lung pathology [7, 10]. Simple effusions will appear as hypoat­tenuating dependent collections, measuring between 0 and 10 Hounseld units (HU) (Fig. 10.5 a, b); hemothorax will have HU between 45 and 65 (Fig.42.5c). Loculated collec­tions are nondependent and have a lenticular shape (Fig.42.6). A parapneumonic effusion is a reactive simple effusion with concomitant pneumonia (Fig.42.7). An empy­ema will demonstrate thickened and enhancing pleural,