1. Katherine Cashen, DO* 2. Tara L. Petersen, MD† 1. *Department of Pediatrics, Children's Hospital of Michigan/Wayne State University School of Medicine, Detroit, MI 2. †Division of Critical Care, Department of Pediatrics, The Children’s Hospital of Wisconsin/The Medical College of Wisconsin, Milwaukee, WI * Abbreviations: BTS: : British Thoracic Society CHF: : congestive heart failure CT: : computed tomography VATS: : video-assisted thoracoscopic surgery 1. Clinicians should be aware of the causes and clinical presentation of pleural effusions and pneumothoraces. 2. Clinicians should understand the current role of diagnostic tests, imaging modalities, and timing of minimally invasive treatments. After completing this article, readers should be able to: 1. Describe the pathogenesis of pleural fluid accumulation. 2. Identify the most likely causes of pleural effusion and pneumothorax. 3. Understand the basic clinical presentation, diagnostic tests, and management of pleural effusions and pneumothoraces. 4. Differentiate between transudative and exudative pleural effusions. 5. Understand the natural history of spontaneous pneumothorax. The pleural space is created by the parietal and visceral pleura that line the chest wall and the lung surface, respectively. Normally, only a small amount (0.3 mL/kg) of hypotonic fluid is present within the pleural space due to homeostatic balances in physiologic fluid production and absorption. Various infectious and noninfectious processes can lead to pathologic filling of the pleural space with fluid (effusion) or air (pneumothorax). Such pathologic changes create a true space that can interfere with normal lung mechanics and, in severe cases, cardiac function. Although much less common in pediatric than adult populations, pleural effusions and pneumothoraces in both groups can lead to substantial complications, resulting in significant morbidity and mortality if unrecognized or untreated. Overall, the cause of pleural effusions and pneumothoraces differs in children compared to adults. In adults, congestive heart failure (CHF) and malignancy account for a substantial number of pleural effusions, but these are uncommon causes in children. Infectious pleural effusions in the setting of pneumonia (parapneumonic effusions) remain the most common cause of effusions in both children and adults. Unlike the adult population, children experience spontaneous …