Expansion
The liver pushes the right dome up; the heart presses the left dome down
Expansion
- Right hemidiaphragm - higher, pushed up by the liver
- Left hemidiaphragm - lower, partly because the heart rests on it and there is no bulky organ beneath
On an erect posteroanterior chest radiograph the right dome normally lies up to about 3 cm above the left. A difference greater than this, or a left dome lying above the right, needs explaining.
Causes of an elevated hemidiaphragm include phrenic nerve palsy, eventration, subphrenic collections and lobar collapse. Remember that the left dome is also the one overlaid by the gastric bubble, which helps confirm which side you are looking at.