Emergencies ) Mediastinal or hilar lymph node enlargement may be the result of malignancy, sarcoidosis, or a mycobacterial or fungal infection Mediastinal tumors that are most likely to produce pulmonary symptomatology include lymphoma, neuroblastoma, pheochromocytoma, ganglioneuroma, thymoma, teratoma, or thyroid carcinoma; however, any malignancy can metastasize to the lungs and cause extrinsic compression of the airways Among the rarest causes of wheezing in children are congenital structural anomalies of the respiratory tract, including bronchogenic cysts, cystic malformations of the lung, congenital lobar emphysema, intrinsic stenosis, and webs Respiratory symptoms typically begin in the neonatal period or early infancy The predominant clinical features are determined by the site of abnormality within the tracheobronchial tree Stridor and a croupy cough are typical of laryngotracheal constriction, whereas wheezing and recurrent pneumonia are more characteristic of bronchial narrowing Respiratory findings generally worsen with intercurrent respiratory infection and may accentuate with crying and activity Some diagnoses are discovered only when persistence of symptoms necessitates imaging studies Bronchiectasis is the term used to describe irreversible bronchial dilatation, and is the common end result of various disease processes The most common cause is CF, but bronchiectasis may also be caused by primary ciliary dyskinesia, immunodeficiency disorders, congenital anatomic abnormalities, and infection Cough is prominent and accompanied by purulent sputum production Even though the diagnosis of bronchitis is more commonly associated with adult patients, children may develop a nonspecific bronchial inflammation associated with various viral agents The pathophysiology is similar to bronchiolitis and may be preceded by upper respiratory symptoms Cough is usually prominent and may be followed by wheezing Other rare conditions are listed in Table 84.2 EVALUATION History Thorough history taking is the key to arriving at an accurate diagnosis in a child with wheezing In particular, consideration of the age at onset, course and pattern of illness, and associated clinical features provide a useful framework for approaching a differential diagnosis ( Figs 84.1 and 84.2 ) In patients with respiratory distress, it may be necessary to perform a focused history pertaining to life-threatening causes of wheezing ( Table 84.1 ) Such a