Page 33 - December 2006 The Game

Canada’s Thoroughbred Racing Newspaper The Game, December 2006 33
THE SINUS SITUATION
We’ve all been guilty at one time or another of accusing a horse of being an air- head. Little do most of us know, however, just how accurate a description that is!
The truth is that much of the horse’s head is hollow. Apart from a brain about the size of a nice, plump lemon, most of the rest of the interior of the equine skull is taken up by the sinuses, air-filled chambers which connect to the respiratory system. It’s actually good that the horse is such an airhead, because if his skull were solid bone, he’d hardly be able to lift it.
All in all, there are three pairs of sinus cavities – the craniofrontal, rostral (or inferior maxillary) and caudal (or superior maxillary) sinuses -- most of which connect to each other, and ultimately drain into the nasal passages. One of the functions of the maxil- lary sinus cavities in the upper jaw is to accommodate the large molars horses need to grind fibre. Like a rodent’s teeth, a horse’s continually erupt up through the gum as they’re worn down from above, and the sinuses provide a place for those long roots to be stored. As the horse ages and the tooth surfaces are ground away, there is more and more air in the sinuses where teeth used to be.
Sinusitis is the catch-all term for inflammation or infection in the sinuses, which can result from several different disease processes, including sinus cysts, ethmoid (nasal cavity) hematomas, tumours, infections of the upper respiratory tract, blunt trauma, fungal infections, and inflamed or abscessed teeth. Whatever the cause, sinusitis tends to demonstrate itself with thick, gunky discharge from one or both nostrils. (If the drainage exit is blocked, the gunk may accumulate and fill the sinus instead.)
There may also be:
• discharge from the eyes
• a distinctive foul smell (especially when there’s a dental issue involved)
• difficulty chewing food
• facial swelling over the sinus area
• signs of discomfort including headshaking or resisting bridling
• laboured breathing or respiratory noises. Diagnosing a sinus problem can some-
times be a challenge. Your veterinarian may start with simple percussion – tapping gently over the sinuses on both sides of the horse’s face. Healthy sinuses will resonate the same way on both sides. Reduced resonance in one area usually indicates that the sinus is fluid-filled or blocked by a mass of some kind. The nostrils will also be examined to see if airflow from them is equal on both sides, and the teeth given a thorough going- over to reveal any potential problems that can be seen from inside the mouth (such as a cracked crown which might let infection get to the root).
If the visual inspection doesn’t illuminate the problem, your vet may suggest radi- ographs. The dense bone of the skull contrasts very well with the air-filled sinuses, so it’s often possible to get a very clear and revealing image. But three-dimensional computed tomography (CT) or magnetic resonance imaging (MRI) can provide even more detail if radiographs don’t do the trick. In several studies of the use of CT imaging on tough-to-diagnose sinusitis, the technology was able to identify individual diseased teeth (showing the fragments of a shattered root or
gas bubbles in the root area)
with pinpoint accuracy, as well
as other features of long-term
sinus disease such as thickening
of the periosteum and subtle
deformation of the bone sur-
rounding the affected sinuses.
Of course, both MRI and CT require general anaesthesia in a hospital setting, so they’re not the first line of defence, but a valid option if you can’t get a clear answer otherwise.
There’s also endoscopy, which allows your vet to examine the opening to the sinuses if not the cavities themselves. Pus coming from the openings is a pretty good indication of sinusitis ... and endoscopy also allows for a view of other structures, such as the guttural pouches, to see if there might be another cause for the nasal discharge.
Treating sinusitis can be difficult because the structures are so tricky to access. So for decades veterinary surgery has taken the direct approach and drilled a small hole in the skull (a technique called trephination) over the sinus cavity. Though it might seem medieval, it’s the best way to get a sample of the fluid for analysis, or biopsy a soft-tissue mass that might be lurking
inside ... and it can
also allow an
endoscope an
interior peek. It is
generally done on-farm under local anaesthesia.
Once the hole has been drilled, the pus can be drained from the sinus by lavage, and your veterinarian might choose to install a drain so you can continue to flush the sinus yourself for the next week or so. It’s sometimes impossible to identify the cause of the infection, or get antibiotics to tackle it effectively, until the gunk has been removed, so this is an essential step.
If the cause of the sinusitis turns out to be an abscessed tooth, then dental surgery may be called for. Sometimes such a tooth can be extracted orally; other times, it may have to be removed surgically, from within the sinus. Sinus cysts (especially those which bulge into the respiratory cavity and interfere with breathing) are also removed surgically, as a rule; fortunately they rarely recur.
Equine Health
by Karen Briggs
Dave Landry Photo
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Season’s Greetings from “Ontario’s most researched horse feeds” dealers:
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A Time to Say Thank You A Time to Care
A Time for Peace & Happiness
Merry Christmas & Best Wishes for a Terrific New Year
From Jockey Jim McAleney & Agent Danny Williams
Horse’s Wish List