Swyer-James syndrome (SJS), also called Swyer-James-MacLeod syndrome (SJMS), is a rare manifestation of postinfectious bronchiolitis associated with adenovirus types 3, 7, and 21; paramyxovirus; morbillivirus; Bordetella pertussis; Mycoplasma pneumoniae; Mycobacterium tuberculosis; and influenza A.
The infectious agents result in an inflammatory response, which causes obliteration of peripheral airways in the infected lung. This inflamation causes obliteration of the vascularity of the lung and impeded lung development. In the long term, destruction of the alveoli and emphysema may occur.
In SJS, because the involved lung or portion of the lung does not grow normally, it 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.
(See the images below.)
Anteroposterior chest radiograph of a 12-month-old patient indicates diffuse pneumonia that is clearing on the right.
Radiograph of the same infant shown in the previous image, now 20 months of age. The pneumonia has cleared. The left lung is hyperlucent and is overexpanded. The right lung is small. The patient was asymptomatic at this time.
SJS is late sequela of bronchiolitis that typically occurs during infancy or early childhood, and affected individuals may be asymptomatic, but more commonly, they have recurrent pulmonary infections and common respiratory symptoms. Adult manifestations of SJS include bronchiectasis, chest pain, wheezing, recurrent bronchitis, hemoptysis, recurrent pneumonia, and bronchial hyperresponsiveness. Given that the initial infection occurs early in life, the diagnosis often is not made until these later symptoms appear.
Diagnosis is made following radiographic evidence of the classic SJS triad: a unilateral hyperlucent lung, diffusely decreased ventilation, and matching decreased perfusion in the affected lung.
The diagnosis of SJS requires the exclusion of many other causes of unilateral hyperlucent lung on chest radiography, including ventilatory abnormalities such as congenital lobar emphysema, bullous emphysema, bronchiectasis with air trapping, emphysema secondary to bronchial stenosis or bronchospasm, and obliterative bronchiolitis, as well as pulmonary artery defects such as congenital pulmonary artery agenesis/hypoplasia, acquired stenosis or compression of the main pulmonary vessels, and pulmonary embolism. None of these ventilatory abnormalities would produce the diffuse, peripheral ventilatory defects on the single breath image and present unilateral lung hypoplasia that the Swyer-James syndrome does. In pulmonary artery defects and pulmonary embolism, there is no air‐trapping on radiologic or ventilation–perfusion lung images.
SJS can be easily misdiagnosed as asthma and should be considered in patients who do not respond to conventional therapy.
Misdiagnosis of SJS as a pulmonary embolism can result in unnecessary treatments and tube placement.
Diagnosis is made radiographically by x-ray and CT scan and is an incidental finding in some cases.
On CT scan, the affected lung displays 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.
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 cause.
Pulmonary angiography is not essential for the diagnosis of SJS, although it can reveal hypoplasia and diminished size of the affected pulmonary artery. Pulmonary angiography, however, has its limitations, as it cannot discern congenital from acquired etiologies of hypoplastic pulmonary vasculature.