Digital radiography and ultrasound are powerful tools that have aided in the life-saving diagnoses and treatments of countless animals. But these imaging modalities are fundamentally limited because they are 2-dimensional projections of 3-dimensional anatomy. In this article we will provide reviews from CT users on the usefulness of this modality with respect to:
- Cancer Staging
- Multi-site pathologies
- Neurological intervention
- Pet-owner compliance
It is often important diagnostically not only to see inside the patient but also to examine the internal architecture of structures within the body. With radiography, you get a 2-dimensional image with all structures superimposed. So, for example, a small pulmonary nodule might be hidden by superimposed structures.
A computed tomography (CT) scan uses the same properties of X-rays and tissues to create a 3-dimensional map of all the tissues in the beam. In the example above, any superimposed anatomy can be digitally removed from the lung to reveal the small nodule. It is this very capability that allows veterinarians to diagnose pathologies with CT that they would not have been able to diagnose with radiography or ultrasound.
Below are some examples of diagnoses that could not have been made without CT technology:
Cancer Staging: “Presented for a right humeral head osteosarcoma. Routine radiography for metastatic disease as part of pre-surgical screening for limb amputation was unremarkable, reviewed by boarded radiologist. CT identified three obvious metastases in the lung fields. Based on radiographs alone, this patient would have been amputated for OSA when they were in fact already terminal.”– PJ Rocheleau, DVM / Espanola Animal Hospital
Multi-site checks: “Presented for acute glaucoma. Eye was non-visual at presentation as seen by a boarded ophthalmologist, referred for eye enucleation. Pre-op CT revealed ocular mass in posterior chamber. While this could have been diagnosed on ocular ultrasound, CT allowed us to also image the regional lymph nodes and thorax (unremarkable, within normal limits). Eye was enucleated, doing great.”– PJ Rocheleau, DVM / Espanola Animal Hospital
Neurological Intervetion: “I spent eight weeks trying to diagnose this little dog ‘Winnie’ that was completely non-weight bearing on the right forelimb. I was never able to localize a specific area of discomfort in any of the joints. No neurological deficits, very minor neck pain intermittently. I spent several nights awake wondering what the hell is wrong with this dog. For eight weeks, she held her leg up. I took tons of radiographs. I did an MRI of the neck with no significant findings. No matter what medications I put her on, she wouldn’t use her leg and I had no idea why.
After an 88-second CT scan and about two minutes of image review, I found a very small piece of calcified disc material that was not compressing the spinal cord but was actually compressing nerve root in the foramina. So random, but a perfect explanation for this dog’s discomfort—a nerve root signature. There’s no other way I could’ve diagnosed this without CT. I kept saying that had to be it, but I just couldn’t prove it.”– Robert Hancock, DVM DACVS / SouthPaws Veterinary Surgical Referral Center
Pet-owner Compliance: A corollary benefit of CT is that it will give you the diagnostic intelligence needed to justify surgical procedures that would have been either questionable or turned down by the pet owner. In the words of Dr. Robert Hancock, DVM DACVS:
“This tool (CT) increases compliance, since you don’t have to be ambiguous with the pet owner with a ‘here’s what we hope to see when we open your pet up’ spiel, where they may justifiably be reluctant to agree to the procedure. A CT can show you exactly where to cut, which tools to bring with you, and give you a very good idea of the clinical outcomes to expect.”
SOUND Top Tip
A useful exercise if you are considering integrating CT into your practice is to sit with a radiologist and review some cases that have presented with multiple imaging studies (radiography, ultrasound, and CT). Your radiologist will be able to quickly point out structures on CT that are not visible (diagnostically) on the other modalities. From there you can better understand the true utility of this advanced imaging.
At some point, your decision to invest—or not to invest—in CT will impact your patient outcomes. CT will help you detect pathologies that cannot be diagnosed with ultrasound or DR, and it may help you avoid unnecessary invasive surgeries and other treatments that would harm your patients.