16. Do you agree so far?
Two very similar projections.
Pleural effusion: left = prone, right = standing up.
We may also demonstrate those effects also by means of sonography.
Difference in diaphragm position proves it is expiration (left) and inspiration (right). Partly encapsulated effusion considerably deforms with breathing.
Subtraction of in- and expiration. It demonstrates diaphragmal mobility and form instability of the mass lesion. This mobility is a good argument for "encapsulated effusion".
There is free air in the abdomen caused by gastric perforation. This thin layer of air causes a (caudal) silhouette of the diaphragm. Thus the thick layer between diaphragm and lung will be a subpulmonal effusion.
A dark line, difficult to pick out, corresponds to paradiaphragmal fat. This gives us an idea of the diaphragm position and of the effusion on top of it:
basal = subpulmonal effusion.