CT Scans Allows Quantitative Wobbler Syndrome Evaluation
Wobbler syndrome—ataxia caused by spinal, or cervical, cord compression—is a diagnosis veterinarians usually reach by looking at somewhat subjective readings of X rays and myelograms. X rays can reveal sites where the cervical canal (which holds the spinal cord) becomes narrower than usual—but that doesn’t necessarily mean the cord is compressed. Meanwhile, myelographies can reveal compression in two dimensions, but doesn’t give veterinarians a look at the sites in more informational 3-D.

What veterinarians really need is an objective diagnostic tool that combines these analyses, showing both the locations of compression and confirmation that the cord is compressed, say Japanese researchers. The computer tomography (CT) myelograph offers just that—but with one significant problem: its size.

“Currently existing CT myelography machines have a small gantry (opening), designed for humans and small animals, and that’s not good enough for horses because we can’t get a picture of the entire cervical vertebral column,” said Kazutaka Yamada, PhD, DVM, of Azabu University’s Veterinary Radiology Department, in Kanagawa.

In their study, Yamada and his fellow researchers examined five ataxic (incoordinated) Thoroughbred foals (aged 5 to 33 weeks) using small-gantry CT myelography under general anesthesia. Afterward, they euthanized the horses and performed postmortem examinations to compare their CT myelography findings to the foals’ actual pathologies.

The scientists were able to scan all seven cervical vertebrae in the two youngest cases, but only the first five vertebrae in the other three, Yamada said. These three horses had already grown too large to fit their necks completely within the machine’s scanning area.

Within the scanned regions, however, the researchers acquired precise, quantitative information about the exact compression locations and the percentage of stenosis (neural compromise) caused by that compression, Yamada said. For example, in the second horse, they found compression at C2-3 with stenosis rates of 47.2%, at C3-4 with 46.3%, and at C4-C5 with 43.5% of the subarachnoid space (the tissue surrounding the spinal cord) and cervical cord. Their visual evaluation of the cervical column postmortem seemed consistent with their CT myelography findings.

While this quantitative information provides much better data for determining treatment and prognosis, it is limited in the fact that it can’t show what’s happening in the vertebrae not represented in the CT myelography due to the size restraints, he said.

However, the size problem should soon be resolved, Yamada said. “Wide-gantry CTs are now available in Japan,” he said. “They were installed in the veterinary schools at Miyazaki University, Kagoshima University, and Obihiro University. The gantry is 90 cm wide (about three feet), so we can obtain whole cervical imaging.”

The timing of this technology is appropriate for this future Olympic host country. “I believe that Japan should prepare this diagnostic tool in the Tokyo area before the Tokyo Olympic Games (in 2020),” Yamada said.

The study, “Quantitative evaluation of cervical cord compression by computed tomographic myelography in Thoroughbred foals,” was published in the Journal of Equine Science.