Although the most common etiology for a pleural effusion in the pediatric population is an empyema, its differential diagnosis is broad and the consequences of mismanaging one are significant. A practitioner should consider malignancy, congestive heart failure, autoimmune, and nephrotic processes, among others listed below, when confronted with an effusion. A careful history and physical examination, in addition to an appropriate workup and laboratory approach when considering the underlying pathophysiology, will prevent most diagnostic errors.

The work of breathing and diminished breath sounds found in pleural effusions, owing to the altered flow and absorption of pleural fluid with resultant compression of the lung, are universal. The confounding symptoms of the effusion, however, are often different because of the speed of fluid accumulation, the patient’s cardiopulmonary reserve, and the associated symptoms of any underlying disease. In the case of pneumonia or other systemic inflammatory process such as a connective tissue disease, fluid accumulates because of the increased capillary permeability of vessels and oncotic pressure of proteins in the pleural space. These patients present with systemic symptoms of inflammation, such as fever and myalgia, in addition to cough or arthritis. In congestive heart failure, the capillary hydrostatic pressure is increased and results in bilateral effusions. Neonates with congenital heart disease commonly present as afebrile, cyanotic, with poor perfusion, and have a murmur. In older patients with congestive heart failure caused by a previously compensated and/or undiscovered congenital disorder, myopathy, myocarditis, pericarditis, or pericardial effusion, the associated symptoms include fatigue, failure to thrive, tachycardia, hepatosplenomegaly, and poor perfusion. Malignancies that result in mediastinal lymphadenopathy or obstruction of the lymphatic ducts, such as in lymphoma or superior vena cava syndrome, prevent lymphatic drainage from the pleural space and often manifest with more indolent fever, weight loss, night sweats, or facial edema. Patients with effusions resulting from nephrotic syndrome with its associated hypoalbuminemia and low plasma oncotic pressure present with
dependent edema—commonly of the extremities, perioral or scrotal areas. Finally, patients who present with trauma, pancreatitis, or Down’s or Noonan syndrome should be considered at risk for evolving effusions.