How to you tell its a right middle lobe infiltrate?

This patient presented with a cough, fever, and dyspnea.  Here is her Chest Xray:

This is a great example of a right middle lobe (RML) pneumonia.  Some features that help distinguish the lobe include:

The right diaphragm is visible.  The lobe overlying the diaphragm is the lower lobe and a RML will sometimes not “silhouette” the right diaphragm.  ”Silhouette” is when a radiographically dense material such as fluid comes into contact with another radiodense thoracic structure such as the diaphragm.  Silhouetting can be seen with the right heart border.  Thus, this fluid on the xray is touching the right heart border but not the diaphragm.  The lobe that corresponds with this is the RML.

A lateral radiograph can also help you identify which lobe is involved (not provided here).

Author:  Russell Jones, MD