Clinical History
A 40-year-old male patient came to the emergency department with a one-week history of fever, cough and haemoptysis.
Imaging Findings
Posteroanterior chest radiograph shows the right pulmonary hilum decreased in size and an asymmetry of the lung vasculature, lower on the right side. The left pulmonary artery shows slight compensatory enlargement and the right lung volume seems slightly decreased (Fig. 1).
CT angiography study confirms the findings described in radiography and displays a heterogeneity in the right lung parenchymal density consistent with a mosaic attenuation pattern (Fig. 2, 3). Cylindrical bronchiectasis, and some cystic, are observed in the right lung, although they are more numerous in the right lower lobe (Fig. 2). Furthermore, there is bronchial wall thickening. No obstruction in the right main bronchus is noted (Fig. 2c).
Discussion
Swyer-James-Mc Leod Syndrome (SJMS) is also known as unilateral hyperlucent lung syndrome. SJMS is generally believed to be a post-infectious complication of viral bronchiolitis or pneumonitis acquired during early childhood. SJMS can result from various lower respiratory tract infections, including adenovirus, measles, pertussis, tuberculosis, or mycoplasma. The infection leads to obliterans bronchiolitis causing inflammation and fibrosis of the respiratory bronchiolar walls and the interalveolar septa which causes reduction of ventilation and distal airways trapping. Secondarily, these changes lead to decrease blood flow to the major pulmonary artery segments which in turn results in the hypoplastic arterial development resulting in pulmonary parenchyma hypoperfusion. [1, 2]
Clinically, most patients are asymptomatic and the disease is often an incidental finding on chest X-ray. However, affected patients may have a history of recurrent pulmonary infection and present with nonspecific respiratory symptoms, such as dyspnoea on exertion, productive cough, and shortness of breath. [3]
The hyperlucency results from air trapping and decreased pulmonary vascular marking in the involved area. The characteristic radiographic findings of SJMS consist of asymmetric hyperlucency of the lung or lobe, small hilar shadow with decreased vascularity, bronchial wall thickening, mediastinal shift toward the hyperlucent thorax, sometimes it can see signs of bronchiectasis. Characteristic CT appearances include lobar hyperlucency due to underlying air trapping, with decreased size of the pulmonary artery and reduction in the number of its branches, bronchiectasis, mosaic attenuation pattern. Expiratory ct images are more reliably in demonstrating air trapping, which is the key finding to differentiate this entity from other conditions. [2, 4, 5]
Among the conditions that may mimic unilateral lung hyperlucency, are the following: Technical problems, chest wall abnormalities (absence or wasting of pectoral muscle, absence of breast, soft tissue surgery, scoliosis, hypolucency of the contralateral lung), parenchymal abnormalities (compensatory overinflation, emphysema, central obstruction of a bronchus, partial bronchial obstruction -foreign body or endobronchial tumour-), vascular abnormalities (pulmonary embolism, pulmonary artery stenosis or agenesis). [5]
The prognosis is generally good. Most patients have an asymptotic course unless the opposite lung becomes diseased. The treatment is generally symptomatic. However, surgery should be considered if secondary infection or bronchiectasis become severe. [1, 2]
Radiologists have a key role in this entity, if the typical findings are present (as in our case, although an expiratrory image would have been desirable) then the diagnosis can be reached without performing other examinations.
Differential Diagnosis List
Swyer-James-MacLeod Syndrome
Technical problems
Chest wall abnormalities
Parenchymal abnormalities
Vascular abnormalities
Final Diagnosis
Swyer-James-MacLeod Syndrome
