result from nontraumatic conditions Necrotizing pulmonary infections, tuberculosis, pulmonary arteriovenous (AV) malformations, torn pleural adhesions, hemophilia, thrombocytopenia, systemic anticoagulation, and pleural tumors have all been reported to cause hemothoraces Chylothorax, or the accumulation of lymphatic fluid in the pleural space, has increased in frequency as thoracic, especially complex cardiac, surgical operations have become more common in children Clinical Recognition Small, sterile collections, as well as large, chronic collections, may be asymptomatic Symptomatic children often present with nonspecific symptoms such as fever, cough, malaise, and anorexia Additionally, acute collections produce symptoms by compressive effects on the lung, with resultant atelectasis, and right-to-left shunting, with resultant hypoxia and hypercapnia Respiratory distress may follow, marked by dyspnea, tachypnea, increased use of accessory muscles of respiration, and even cyanosis Small to moderate effusions may not be evident on physical examination, with most effusions detected by chest radiograph Larger effusions will cause dullness to percussion and decreased breath sounds Small effusions can be quite subtle and may manifest as slight blunting of the costophrenic angle on chest x-ray Larger effusions may cause significant opacification of a hemithorax and may layer out on an upright view of the chest, creating the so-called “meninscus sign.” Chest radiographs may also demonstrate the likely etiology of the effusion since cardiomegaly, mediastinal masses, and hilar lymphadenopathy may all be appreciated Moderate to large effusions on chest x-ray merit further evaluation by ultrasound to further characterize the effusion and determine whether it is comprised of free fluid or a loculated collection In skilled hands, ultrasound provides more information than either decubitus radiographs or CT and has the obvious advantages of not requiring sedation or exposing the child to radiation Management Children with pleural effusions should have peripheral blood counts and blood cultures obtained since parapneumonic collections are the most likely culprit Many small effusions can be managed conservatively with treatment of the underlying disease For moderate or large effusions, drainage of pleural fluid, or thoracentesis (see Chapter 130 Procedures ), may be necessary Thoracentesis may be therapeutically indicated for significant respiratory distress or