Imaging the Lungs In Small Animals & Horses: A Two-Pronged Approach

by Susan Keane MVB MANZCVS DABVP, staff veterinarian for BCF Ultrasound. 

 

One major contrast between small animal and equine medicine is the diagnostic approach to respiratory disease….

  • Which diagnostic modality will a horse vet reach for first in a coughing foal ?…. Lung ultrasonography
  • Which modality will a small animal vet reach for when dealing with a dyspnoeic cat?…. Thoracic radiography

It turns out that BOTH of these modalities should be used to complement each other if possible … Equine vets have X-ray machines and small animal vets have ultrasound machines, but sometimes it’s easy to forget to about using them in different ways…

 

The Equine Example

Lets think about the 8 week old, ill-thrifty foal that’s been heard coughing. Pulmonary Rhodococcus equi infection is going to be your number one differential. And in the majority of these cases, changes will be found on ultrasound. These include “comet tails” (A.K.A. “B-lines”), areas of consolidation or abscessation. BUT, remember that with ultrasound you are only looking at the surface of the lungs on both sides.

This is one case example that jumps out at me from early in my career:

An 8 week old foal presented to the hospital with severe pyrexia, lethargy and markedly increased respiratory rate and effort. There were just mild comet tail artefacts on lung ultrasound, but on radiography, 3 large mediastinal abscesses were evident! 

In practice, your portable radiography machine is perfectly capable of getting great shots of even adult equine lungs! You just need to be cognisant of radiation safety – lining the plate and beam up correctly and ensuring your plate holder is standing in a safe spot. 

 

The Small Animal Example

It is true to say that radiography is the mainstay of thoracic imaging in small animals – you can learn a lot about both the lung and heart from good radiographs. That’s why many small animal vets overlook lung ultrasound and say “what benefit does it have?”.

Let’s take the case of the dyspnoeic cat that needs to be stabilised immediately on admission. In these cases, a quick TFAST exam can be performed while administering oxygen therapy and getting everything set up. Just part the hair, spray some alcohol on the areas you are going to examine and stick the probe on. Within seconds, you will be able to determine if there is free fluid in the chest or “comet tails” (“B-lines”) on the lung surface. You will have narrowed down your differentials rapidly and be able to come up with a more accurate therapeutic plan for that patient.

Here are some case examples of what you might find on ultrasound in your small animal respiratory cases:

Next time you have a respiratory case, try to make use of all the modalities you have at your disposal. Let us know about cases that you have had where performing both radiography AND ultrasound was key to diagnosis…

 

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