esophageal foreign body or a significant history of forceful emesis, an esophagram using water-soluble contrast may be helpful In the extremely rare case of a tension pneumomediastinum, evacuation of the accumulated air in the mediastinum is necessary FIGURE 124.6 A: Significant pneumomediastinum with accentuation of the cardiac silhouette B: A far more subtle pneumomediastinum in an asthmatic patient with chest pain Pleural Effusion Pleural fluid in excess amount is not a disease per se, but it indicates the presence of pulmonary or systemic illness The classification of the fluid into transudate , which accumulates when the normal pressure relationships between the capillary pressure in the lung, the pleural pressure, and the lymphatic drainage pressure are disturbed, or exudate , an inflammatory collection, has less utility today because of other diagnostic tools presently available Nevertheless, it is important to recognize causes of transudative fluid collections, including increased pulmonary capillary pressure (as in congestive heart failure), decreased colloid osmotic pressure (as in renal disease), increased intrapleural negative pressure (as in atelectasis), or impaired lymphatic drainage of the pleural space (e.g., from surgical trauma to the thoracic duct) In children, the inflammatory cause of effusion is most commonly a result of pneumonia, with accumulation of infected fluid in the pleural space, or empyema (see below) Malignant effusions from associated oncologic diagnoses are much less common than in adults, but also occur in children The accumulation of blood in the pleural space because of trauma is discussed in Chapter 115 Thoracic Trauma Hemothorax may also