Copyright © 2009 [Gerald R. Aben, MD MSU Department of Radiology]. All rights reserved.
Revised: April 08, 2009
Step-by-Step Approach

 

Evaluating the Chest Radiograph

Step 6:  The Heart

The heart silhouette offers considerable direct and indirect information.   First, cardiac size and chamber enlargement can be inferred by evaluation of the chest radiograph.   The normal heart will occupy slightly less than 50% of the transverse dimension of the thorax.  This is evaluated by measuring the greatest transverse (across) diameter of the heart on the frontal projection and relating that to the greatest transverse measurement of the internal dimension of the chest.   This measurement is best made with a ruler, although, I would hazard a guess that most of you will find that measurement made using your thumb and little finger will suffice in most instances. 
 
The black double headed arrows demonstrate where the heart should be measured.

 

As your skills improve, additional reading could guide you into the art of evaluating specific chamber enlargement by analysis of the chest radiograph.  

 

Various anatomic features of the heart are labeled.

 

The fact that the right and left heart borders are in direct contact with the lungs adds a useful diagnostic tool to your imaging tool belt.   When space occupying disease involves the lung adjacent to the heart, the air heart interface disappears.  This silhouette sign will alert you to the presence of Right Middle Lobe air space disease when the right heart border disappears and Left Upper Lobe (Lingular segments) airspace disease when the left cardiac border disappears.

 

Black arrows indicate the loss of the cardiac border, white arrows the infiltrate in the middle lobe.
 
The left heart border is obscured by a large infiltrate in the left upper lobe.

 

Without a doubt, tumors, being space occupying abnormalities can also silhouette the heart.   Advanced pulmonary edema, also an air space disease can cause loss of the heart border as well.

Diffuse pulmonary edema has obscured both right and left cardiac margins in this patient.  The right diaphragm is also somewhat obscured.