Swyer-James syndrome (SJS) is a manifestation of postinfectious obliterative bronchiolitis. In SJS, the involved lung or portion of the lung does not grow normally and is slightly smaller than the opposite lung. The characteristic radiographic appearance is that of pulmonary hyperlucency, caused by overdistention of the alveoli in conjunction with diminished arterial flow. [1, 2, 3] (See the images below.)
Swyer-James syndrome refers to an inability of the lungs to grow after a severe obstructive bronchiolitis. On CT scan, the affected lung shows small size and decreased vascularity, hyperexpansion and hyperlucency, and, rarely, bronchiectasis. For patients with Swyer-James syndrome, chest CT scanning with thin collimation sections on inspiration and expiration is the preferred examination. [4, 5] The appearance of the lungs on forced expiration is important in the assessment of SJS with CT scanning; therefore, the patient's cooperation is essential. The patient should be placed in the prone position to help identify the typical mosaic pattern of the syndrome.Small regions of hyperlucency representing air trapping are reported in some patients. Adenovirus infection is considered the most usual epidemiology. Patients respond well to management with bronchodilators, even though this is not primarily a bronchial abnormality.
Radiographically, the imaging findings of SJS appear a few months to a few years after the causative infection. The typical appearance of Swyer-James syndrome is that of a small, hyperlucent lung, with overexpansion of the contralateral lung. A diffuse pattern of scarring or irregular vessels may be present.
A comparison of progressive radiographs shows failure of growth in the involved lung. Fluoroscopy shows little change in volume in the involved lung with respiration. (See images below.)
The disparity in size between the 2 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 in making the diagnosis.
In Swyer-James syndrome, the bronchi have a pruned appearance. A mosaic pattern of air trapping in acini is seen, along with air trapping during expiration. The appearance is similar to that of hypoplastic lung syndrome. [6, 4, 5]
In addition, the appearance of Swyer-James syndrome is the same as that of bronchiolitis obliterans, but bronchiolitis obliterans is more frequently a diffuse process.
Magnetic Resonance Imaging
In Swyer-James syndrome, the pulmonary vessels of the affected lung appear smaller than normal on magnetic resonance imaging (MRI) scans. Peripheral branches of the pulmonary vessels do not develop, and vasculature is arrested at the stage at which the infection occurred.
On ventilation-perfusion lung scanning, diminished activity of the affected lung is seen with perfusion scanning, and decreased gas exchange is seen during the ventilatory phase. The lung perfusion deficit seen in patients with Swyer-James syndrome occurs because the peripheral branches of the pulmonary vessels have not developed normally, and vasculature is arrested at the stage at which the causative infection occurred.
Any disorder involving distal airway obstruction (ie, bronchiolitis obliterans, asthma, congenital lobar emphysema) may present in the same manner as Swyer-James syndrome, resulting in a false-positive result.
In patients with Swyer-James syndrome, the pulmonary artery and its branches are small and hypoplastic on the involved side. Collateral vessels may be present, but they are unusual.
However, acquired hypoplastic lung cannot be differentiated on angiography from congenital hypoplasia of the lung. Swyer-James syndrome is also similar in appearance to lobar emphysema and hypoplastic pulmonary artery.