Swyer-James (MacLeod’s) syndrome is a form of Bronchiolitis obliterans that results in unilateral air trapping caused by obstruction of small distal bronchi as well as bronchioles following an insult in the developing lungs. The lung served by abnormal airways remains inflated by collateral air drift. Typically it is unilateral and a whole lung is affected, but changes may be confined to a lobe or segment. The lung tissue is hypoplastic, including the pulmonary artery and its branches, which are reduced in both size and number. The most common cause is acute viral infection in the immature lung during the first eight years of life before the lung has completed its development. Implicated viruses include adenovirus and measles virus. Other possible causes include non-viral infections (Mycoplasma pneumonia, tuberculosis, pertussis infection.), toxic fumes, lymphoma, lung cancer, organ transplant, associated collagen vascular disease, and idiopathic causes. Patients usually present as asymptomatic adults with an abnormal radiograph. Occasionally patients present with exertional dyspnea. Unilateral hyperlucency is caused by reduced lung perfusion, and if confined to a lobe, the hyperlucency is lobar. The size and number of peripheral vessels are reduced on the affected side with increased blood flow to the contralateral lung. The mediastinum may show some shift to the affected side at total lung capacity. The fact that the ipsilateral lung volume does not increase is helpful in distinguishing Swyer-James syndrome from emphysema per se. Ipsilateral air trapping is a key finding and can be demonstrated with two chest radiographs – one in expiration and another in inspiration.

Congenial lobar emphysema is the over distention of one or more lobes of the lung but not usually the entire lung. The postulated basis for the overdistention is bronchial obstruction; however the precise cause of the obstruction is unknown. Approximately 10% of patients with congenital lobar emphysema have congenital heart disease. Patients with this condition usually present in the neonatal period with respiratory distress, however may be asymptomatic until later in life. The most common radiographic appearance is hyperexpansion of an isolated lobe in one lung. The typical distribution of occurrence follows:
-   Left upper lobe (40%)
-   Right middle lobe (35%)
-   Right upper lobe (20%)
-   2 lobes affected, 5%
-   Lower lobes involved (2%)
The hyperexpanded lobe may cause displacement of the heart, mediastinum, and diaphragm as well as compression atelectasis of the rest of the lung. Other causes of obstructive overinflation that may mimic congenital lobar emphysema are as follows:
-   Idiopathic (50%)
-   Obstruction of airway with valve mechanism (50%)
·   Bronchial cartilage deficiency or immaturity
·   Mucus
·   Web, stenosis
·   Extrinsic compression


In addition to plain radiography CT and V/Q scans both have roles in the diagnosis of both Swyer-James syndrome and Congenital lobar emphysema.