Swyer-James syndrome is post infectious obliterative bronchiolitis, usually a result of childhood infection. Commonly (on board examinations), it is described as "unilateral hyperlucent lung."

However, it often does not involve the entire lung, as in this case¹. This is because the point of bronchial obstruction is in the small airways (bronchiolitis), not the larger segmental or central bronchi.

There is right lower and middle lobar hyperlucency, with a few scattered areas of mosaicism within the right upper lobe. There is corresponding diminished size of the pulmonary vasculature supplying the right middle and lower lobes. The left lower lobe has a few very faint areas of mosaic attenuation.