Background: Swyer-James syndrome (SJS) is a manifestation of postinfectious obliterative bronchiolitis. The involved lung or portion of the lung does not grow normally and is slightly smaller than the opposite lung. Radiographically, pulmonary hyperlucency caused by overdistended alveoli combined with diminished arterial flow characterizes its imaging appearance.

Pathophysiology: The lung is expected to grow by progressive alveolarization for a child's first 2-8 years. Thereafter, lung growth is related to hyperexpansion of existing alveoli. SJS is a postinfectious syndrome in which diminished vascularity, arrest of progressive growth and alveolarization of the lung, and resultant hypoplasia occur. Multifocal areas of air trapping may be seen. The pulmonary parenchymal pattern is similar to obliterative bronchiolitis.

Frequency:

• In the US: An unusual manifestation, SJS has been described following infection by Mycoplasma pneumoniae and Streptococcus pneumoniae, as well as following severe respiratory syncytial virus infection.

Mortality/Morbidity: As a complication of infection, SJS is followed by chronic lung disease showing bronchiolar abnormality, air trapping, and abnormal lung dynamics during inspiration and forced expiration.

Age: The effect of decreased vascularity and lack of growth in the involved lung is characteristic of children younger than 8 years (ie, below the age of complete alveolarization). Radiographically, the imaging findings of SJS appear a few months to a few years following the causative infection.

Anatomy: Patients with SJS have a small lung, compensatory overexpansion of the contralateral lung, peripheral bronchi and bronchioles "pruned" secondary to obliterative bronchiolitis, a mosaic pattern of hyperlucency on CT, and small vessels and vascular occlusions in the abnormal areas.

Clinical Details: Typically, the child had severe pneumonia earlier in life. SJS effects are as follows:

• Areas of lung hyperlucency

   

• Air trapping upon expiration

   

• Bronchial/bronchiolar disease with wheezing

   

• Unilateral small chest

   

• Abnormal time-attenuation curves during inspiration and forced expiration

Organisms causing the infection include respiratory syncytial virus, influenza virus, Mycoplasma pneumoniae, and staphylococcal and streptococcal infections.

During differential pulmonary function testing, the involved lung shows diminished flow and oxygenation, and prolonged forced expiratory volume in 1 second.

Preferred Examination: Chest CT with thin collimation sections and on inspiration and expiration is the preferred examination.

Limitations of Techniques: An important feature of CT is the appearance of the lungs on forced expiration; therefore, the patient's cooperation is essential. Place the patient in the prone position to help identify the typical mosaic pattern of SJS.

DIFFERENTIALS

Airway Foreign Body
Bronchiolitis Obliterans Organizing Pneumonia
Bronchopulmonary Dysplasia
Congenital Lobar Emphysema
Emphysema

Other Problems to be Considered:

Bronchiolitis
Bronchial adenoma
Bronchial granuloma

X-RAY

Findings:

• The typical appearance is a hyperlucent but small lung with overexpansion of the contralateral lung.

   

• A comparison of progressive radiographs shows failure of growth in the involved lung.

   

• A diffuse pattern of scarring or irregular vessels may be present.

   

• Fluoroscopy shows little change in volume in the involved lung with respiration (see Images 1-4).

Degree of Confidence: The disparity in size between the two lungs may represent a hypoplastic pulmonary artery or congenital hypoplasia of the lung. A comparison with a previous set of radiographs helps with the differential diagnosis. A history of severe lung infection also helps determine the diagnosis.