Soft Tissue Infections

So you have a patient that has a painful and red area on his thigh, how can you use ultrasound to differentiate the type of infection: cellulitis, abscess, nec fas?

The normal structure of the skin. Notice how well organized everything is.

 Now, if you look at edema within the soft tissue you will note that fluid is collecting within the soft tissue planes, spreading them apart.  This first becomes appart as a phenomennon called columning.  The fluid appears to create black columns that appear to seperate the tissues and destroys the architecture.

As the infection progresses, edema seperates the tissue planes further, illustrating individual fat lobules.  Now the soft tissue takes on the appearance of a cobblestone street.  This appearance is called cobblestoning and further demonstrates cellulitis.

Eventually the infection coalesces and collects into a pocket of fluid or pus, creating an abscess.  An abscess will appear as a irregularly shaped fluid collection which appears to have tenticles that reach into the surrounding soft tissue.

Can you see the difference?

So how do we scan our patient?  First start with a high frequency probe to give us a lot of detail and place it on the small parts setting

Then start with an area that is not affected adjacent to your area of interest.  Scanning here briefly will allow you to see the normal structure of the tissue so that as you slide over to the affected area, the edema and disruption of the tissue plane becomes more apparent.  Slide over the affected area in both a long and transeverse plane to clearly image the area in all dimentions.  If a fluid collection is seen, compress it gently.  Many times when an abscess is present you can see the purulent matrial within swirl around.  This finding confirms that this is an abscess.

So now there should be no question as to whether to open up an area or to give antibiotics and warm compresses and discharge for a recheck in 48 hours!