The mediastinum is comprised of superior, anterior, middle, and posterior compartments; however, masses in the anterosuperior compartment of children can be extremely unstable and challenging for caregivers. A mass in this location may result in life-threatening airway obstruction, and can arise unexpectedly at any time and cause cardiac or pulmonary artery compression, or acute pulmonary edema from superior vena cava syndrome (SVCS), all of which represent true emergencies that mandate prompt treatment.

Compared with an adult, small decreases in a child’s tracheal diameter produce larger decreases in cross-sectional area and airway resistance. The most common presentation of an anterosuperior mediastinal mass is stridor, dyspnea, and cough due to direct compression of the tracheobronchial tree. Often these children even require oxygen at presentation. Examination may demonstrate reduced breath sounds or rhonchi on auscultation, tachypnea, prolonged expiration, accessory muscle use, or cyanosis. However, patients may not be symptomatic and plain chest radiographs may not reveal the presence of airway compromise. Some studies, such as pulmonary function testing, can help to predict airway complications if they demonstrate flattened flow volume loops where expiratory flow is significantly diminished. Cardiorespiratory complications may occur abruptly in these patients and are often not related to mild preoperative symptoms and roentgenographic evidence. Extrinsic compression of the trachea or mainstem bronchi can cause significant airway obstruction and is a cause of death or morbidity with induction of or emergence from sedation or anesthesia. It is also important to understand that there is most likely some degree of SVCS in all children with anterosuperior mediastinal masses, which also can cause severe complications with any sedation.

Clinical manifestations of severe SVCS include variable degrees of face, neck, and upper thorax swelling; external jugular and superficial chest vein distension with possible cyanosis; and plethora. Cardiac or pulmonary artery compression and acute pulmonary edema can represent the initial clinical
signs in previously healthy children. Upper body venous hypertension impedes lymphatic drainage, often leading to lymphedema or chylothorax. Although venous pressures are raised, it is not uncommon to find that edema and plethora are more impressive than large surface vein dilation. The most common cause of SVCS is surgery for congenital heart disease; the second most common cause is anterosuperior masses. Usually these masses are malignant lymphomas (usually found in adolescents) or germ cell tumors (children). Two thirds of the germ cell tumors are benign teratomas.