Figure 6a. Effect of breathing on the mediastinum. (a) CT scan shows the needle (arrow) in a parasternal location, a small anterior mediastinal lesion (arrowhead), and a potential extrapleural window. (b) CT scan obtained a few seconds later shows interposition of the lung in the path of the biopsy needle (arrow); this interposition is caused by variation in respiration and precludes extrapleural biopsy. Note that the target lesion is no longer seen in the biopsy plane.