The left hemidiaphragm should be visible behind the heart
The hemidiaphragm contours do not represent the lowest part of the lungs
The diaphragm separates the comparatively dense (whiter) abdominal organs below it, from the relatively less dense (blacker) lung above. Each hemidiaphragm should appear as a rounded, domed structure with a crisp white edge contrasted against the adjacent dark lung.
The right hemidiaphragm is usually a little higher than the left, to accommodate the liver.
Very often you will see air in the stomach below the left hemidiaphragm, with the appearance of a dark (less dense) bubble. It is important to be aware that the lowest portion of the lungs, which lie in the posterior costophrenic recesses, lie below the level of the contours of the hemidiaphragms, and occasionally the stomach bubble forms a window through which this part of the lung is visible.
The left and right hemidiaphragms are almost superimposed on a lateral view. Anteriorly the left hemidiaphragm blends with the heart and becomes indistinct.
Assessing the diaphragm
The hemidiaphragms are domed structures that should be well defined and visible to the midline on a frontal view. The contours of the hemidiaphragms do not form the bottom of the lungs. Lung markings can be seen below the hemidiaphragms. The stomach bubble, which is a normal phenomenon, and the soft tissues of the abdomen are also visible below the hemidiaphragms.
