Swyer-James (also known as MacLeod) syndrome is a form of bronchiolitis obliterans, which occurs secondary to injury to the immature lung. The lung served by the damaged airways is aerated by collateral air drift through the pores of Kohn. It typically presents as an incidental finding on CXR performed for unrelated reasons.

On CXR, the affected lung is of small or normal volume. Unilateral transradiancy is detected in severe cases. The affected side shows a reduction in size and number of pulmonary vessels (with reduction in size of the hilum), whilst the contralateral side looks plethoric.

HRCT additionally demonstrates that the findings of air trapping are often bilateral (CXR is not sensitive enough to demonstrate bilateral changes). Bronchiectasis is a common additional finding.

The most important differential to exclude is a central obstructing lesion causing air trapping.