The Power of the CT Scan (and Other Tales from Vincent’s Big Day in the OR)
Posted Aug 30 2010 5:57am
If you’re among those pet owners that have been unlucky enough to have lived through serious problems with your pets — yet fortunate enough to have the means (financial or otherwise) to deal with them — you’re probably already aware of the rising importance of the CT scan in veterinary medicine.
Here’s some background for the most avid vet voyeurs among you
In the 1960s and ‘70s, veterinarians were busy buying up X-ray machines — big, hulking, melamine-topped tables with huge cathode ray tubes suspended menacingly overhead. Along came the ‘80s and ‘90s, when the ultrasound revolution swept through vet medicine.
No, ultrasounds would not replace X-rays. Not only because each imaging approach offers its own unique set of pros and cons, but also because their significant expense and steep learning curve still proved best suited to those who could dedicate themselves seriously to this study. Also because it's a common joke that the term "diagnostic ultrasound" is an oxymoron. And you know what they say about the best jokes: they're never too far from the truth.
Hence, an ultrasound for each and every practice started to seem like serious overkill. (Sure, you can get a machine for $10K, but do you really want it for more than bladder sticks and preg checks?)
Next came the latter ‘90s, and with vet specialization in full swing, specialty practices were able to spend their collective bucks on serious power tools. That’s when the CT scan made its big entry into the word of vet medicine.
"CT" — as in computed tomography (aka "CAT Scan") — is a medical imaging method that uses a computer mapping system to generate a three-dimensional image of a patient. This is accomplished by reorganizing the data from a huge series of two-dimensional X-ray images that are taken as the patient lies in a tube shaped structure.
The idea is this: if a picture is worth a thousand words, how much is a 3-D reconstruction based on thousands of images worth?
Priceless, right? Well … not exactly. I’ve paid up to $2,900 for a CT for my pets (though the steepest fee was eventually discounted out of "professional courtesy"). I’ve heard that in some parts of the country a CT can even go for $4K, depending on the ancillary issues involved (serious anesthetic requirements/limitations, for example).
Price aside (tacky to bring up money so quickly), the critical issue with CTs is this: sometimes no other imaging study will do (imagine trying to identify the margins of a brain tumor with a simple X-ray). Other times we employ it because it’s the least invasive approach. Of course, all that exposure to X-rays is not something we take lightly (I would never advocate an annual CT as a simple screening, as some human-care practitioners have advocated to their patients), but we’ll almost always prefer a radiation-riddled CT over invasive exploratory surgery.
In Vincent’s case, the CT was considered the best way to look into his spinal canal in search of areas where abnormal vertebrae or diseased disc material might be compressing his cord. Problem is, Vincent’s spine is so deformed that the radiologist easily ID’d multiple areas where compression might be taking place.
Here's a pic of the disaster that is his spine ("The spine from hell")
Here's a close-up of those nasty hemivertebrae (aka "butterfly" vertebrae)
The tight spots were, 1) over his thoracic spine (where an explosion of hemivertebrae apparently took place during Vincent’s embryological development — see arrows); 2) in his lumbar spine, where two intervertebral spaces (L4-L5, L5-L6) had some mineralized disc material popping down onto the canal; and 3) in the spinal cord’s hinterlands at the lumbosacral space — tight in there. Could there be some sick disc material accounting for that? Very likely, from the looks of it.
The thing is, Vincent’s clinical signs were most consistent with either the lumbosacral lesion or the lower lumbar spots. But we couldn’t tell whether the spinal cord was actually being compressed or not — not without a way to highlight the spinal cord itself. Hence, the need for a second CT experience, this time with contrast material added to highlight the degree of insult the cord is actually experiencing.
Now, one great reason to use a CT is so you can get away with not applying an invasive technique like the myelogram. But sometimes it’s needed to ensure that we reach the right diagnosis. With a myelogram, contrast material is injected into the space surrounding the cord. Here's Vincent, anesthetized, awaiting word on the success of the study alongside his favorite vet tech, Laura
It’s sort of like the epidural anesthesia experience some of us have experienced — except with lots more headachy-ness and residual discomfort (if what humans experience is any guide), and a reasonably high risk of a serious reaction to the material itself. Yes, sudden death can happen during myelograms, which is one reason veterinarians make you sign all those fiddly forms before we undertake tough procedures like these.
Vincent powered through nicely, though, and by day’s end the radiologist had confirmed the surgeon’s read of the study, whose diagnosis had been to cut the lumbosacral spot — which he then did. And when he did, a big blob of disc material was sitting right there, begging to be removed. Now for the scary stuff: applying cold steel to what is perhaps the most vulnerable bit of mammalian anatomy in an effort to free the spinal cord of this miserable junk.
As you already know from yesterday’s post, Vincent did a great job recovering. He spent the weekend in something of a post-fentanyl haze, so I didn’t expect to see miracles of improvement in his function. Still, he’s walking, wanting to jump (I will not be letting him get away with this), and begging for more food to fatten up his frame (which I will also not be letting him do).
In fact, Vincent is already better than before, neurologically speaking. Which is a whole lot more than I can say for my cable modem (still not fixed despite the cable man’s visit). My car’s recently "repaired" AC relapsed over the weekend (this will be the third trip to the dealership on this one issue), and two different repairmen can’t seem to agree as to whether my lightning-struck washer and dryer are truly dead or not.
Which makes me wonder: Mechanical devices being less fiddly than biological organisms and all … maybe what these unhappy appliances really need is something that has become disturbingly hard to find — someone who actually knows what s/he’s doing. Sad, innit?
Dr. Patty Khuly
P.S. - I know some of you will invariably ask the question: Why not an MRI? Here's my answer: The MRI is unquestionably a superior tool for soft tissue evaluation, with no radiation fears. And with it, we would not have needed to do a myelogram. Compression of the cord would have been visible. In Vincent's case, however, we really needed a CT, seeing as his obvious bony malformations were high on the list of possible causes for his clinical signs. Ideally, we would have done a CT and then an MRI. All the specialty hospital needs now is a few hundred thousand dollars for a (used) MRI machine. Maybe next year. ;-)
Here are another couple of pics to illustrate his "poor posture." In this one he's actually sitting up on his forelimbs, not "frog-sleeping." Decidedly abnormal.
Here's another pic to give you a clearer picture of his loss of function. His toes are all "knuckled" over. His brain is not getting great reception on that channel.