Head First: Equine Head and Sinus Issues
Issues that can affect your horse’s head structures, from his lymph nodes to his nostrils
A soft eye, a velvety muzzle, a forelock adorning a smooth face—these are just a few of the attributes of the equine head that beckon horse lovers. Then there are the lumps, bumps, discharge, and drool, which can be unsightly signs that something’s not quite right with a horse’s noggin. And so much lies beneath the hard equine skull that it’s often difficult to know when something is wrong just by visual inspection, much less whether it’s benign or dangerous.
From infections and trauma to blockages and growths, here’s what your vet might find within your horse’s head region.
The Inner Workings
The equine head, which accounts for 10% of a horse’s total weight, houses a series of intricate turbinates within the nasal passageways. Turbinates are a network of bones, vessels, and tissue that warms, humidifies, and filters the air the horse inhales. In addition, seven air-filled sinus cavities called the paranasal sinuses sit on each side of the head, above, below, and between the eyes. A young horse starts out with teeth that extend up into the sinuses; with wear and age, the teeth descend into the mouth. Eventually, in a horse’s golden years, the sinuses are mostly empty of teeth.
The head also contains a plexus of nerves and blood supply in addition to the eyes, ears, nostrils, lymph nodes, guttural pouches (cavities in the back of the head), brain, and more than 30 bones.
When Something’s Wrong
If your horse displays signs such as nasal discharge or bleeding or facial trauma, growths, or swelling, your veterinarian will try to track down the source.
“A physical exam gives a basic external overview of the sinuses and skull,” says Chris Bell, BSc, DVM, MVetSc, Dipl. ACVS, owner of Elder’s Equine, in Mani- toba, Canada, and adjunct professor at the Western College of Veterinary Medicine, in Saskatchewan. “We can detect trauma; masses; bony changes or swell- ing, including bone abnormalities in the jawbones (maxilla and mandible); muscle loss; cranial nerve (which control the facial muscles and certain functions, such as sight, smell, and hearing) dysfunction; injuries or abnormalities of the eyes, ears, and nose; and abnormalities in the TMJ (temporomandibular joint) region.
“We look for symmetry of the structures on either side of the head,” he continues. “If an imaginary line is drawn down the center of the forehead, the anatomy on each side should mirror the other. We check for sensation and tone of the muscles to assess cranial nerves. We further examine the eyes, ears, nose, and mouth for signs of injury or abnormality.”
Jose Garcia-Lopez, VMD, Dipl. ACVS, ACVSMR, associate professor of large animal surgery and director of equine sports medicine at the Cummings School of Veterinary Medicine at Tufts University, in Medford, Massachusetts, says percussion (tapping on the head) can reveal abnormalities in a sinus cavity. “Normally, the sinus is full of air but a duller sound than expected points to possible fluid or tissue buildup,” he says.
“An oral exam tells much about a horse’s ability to eat and breathe normally,” says Bell. “Looking inside the horse’s mouth allows examination of the tongue, hard and soft palate, the interior of lips and cheeks, as well as a comprehensive evaluation of the teeth.”
Garcia-Lopez says an oral exam also allows the veterinarian to identify gaps between teeth that might serve as tracts or fistulas (abnormal connections) into a sinus cavity.
If these exams don’t pinpoint a problem, the next step depends on why the owner called the vet, says Bell. He and Garcia-Lopez use upper airway endoscopy (running a long, flexible tube with a camera at the end through the horse’s nostril down into its airway) to seek a reason for upper airway noise, restricted air passage in either or both nostrils, or persistent nasal discharge. This procedure also allows them to evaluate laryngeal structures without sedation.
“We look for inflammatory polyps in the pharynx (the area extending from the rear of the mouth and nasal passages to the larynx and esophagus), displacement of the soft palate (the soft, fleshy posterior partition separating the nasal and oral cavity at the rear of the mouth), collapse of the dorsal (top of the) pharynx, fungal growths in the nasal passages, an ethmoid hematoma (more on this in a minute), drainage from guttural pouch openings, as a few examples,” says Bell. “Other important areas to survey are the temporohyoid joint (which attaches the hyoid apparatus—bones that hold the larynx in place—to the base of the skull) and the stylohyoid bone (part of that joint, located near the middle ear and guttural pouch), both of which are important to tongue and neurologic functions of the head.”
Radiography (X ray) is another imaging modality helpful for diagnosing sinus and head conditions, such as the presence of free fluid, masses, tooth root issues, sinus cysts, or fractures of the skull, teeth, jawbones, and sinuses. Any abnormality identified with radiographs might prompt veterinarians to pursue other imaging options, such as a computed tomography (CT) scan to review the anatomy in 3D.
Bell says nuclear scintigraphy (bone scan) helps him evaluate stress fractures, irregular tooth root and tooth crown is- sues, and suspected bone tumors, while MRI is useful for evaluating soft tissue masses, the brain, eyes, abnormal fluid, and nerves. Sinoscopy (inserting a rigid endoscope into a small hole drilled into the sinus) allows him to view soft tissue masses (e.g., tumors) and guide a biopsy instrument for taking tissue samples. A PET scan lets him look at the characteristics of a suspected sinus tumor to determine if the mass is malignant or benign.
A primary bacterial infection might cause this sinus infection. A one-sided mucopurulent (containing mucus and pus) nasal discharge is typical of an infected sinus cavity. Lower airway infections tend to, but don’t always, involve discharge from both nostrils. It’s also possible for this bilateral nasal discharge to occur with a sinus infection or cancer.
Horses with pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease) often experience infections, including in the sinuses. “The sinuses in horses are prone to infection, as they are closed, with only a single drainage point, and inhabited by respiratory bacteria and viruses just waiting for opportunity,” says Bell. “Immune suppression caused by PPID provides the opportunity.”
Nasal drainage associated with a tooth infection is usually extremely foul-smelling due to the presence of anaerobic (not requiring air to survive) bacteria. Infection caused by food impaction in a tooth can ascend through periodontal tissue into a sinus. A visible enlargement might appear around the maxillary bone (part of the upper jaw) with a tooth and/or sinus infection.
Ethmoid hematoma (EH)
Blood drainage from one or both nostrils (epistaxis) might foretell the presence of this blood-filled noncancerous polyp within the sinus or nasal cavity. The bloody discharge might occur intermittently or persist for longer periods.
“In some cases an EH within the sinus is not readily visible during endoscopic examination; a CT scan helps to identify these cases,” Garcia-Lopez says. Vets usually base their diagnosis on a history of nosebleeds, plus endoscopy findings.
Garcia-Lopez uses endoscopic guidance to inject the chemical formalin directly into the EH. Other options include surgical or laser removal. Bell adds that surgical removal has good success rates out to about five years. Recurrence is common, so he recommends having your veterinarian re-examine the area annually.
Blunt force, such as from a kick to the head, can result in fracture of the thin bones over the sinuses or elsewhere on the head. Fractured bones over a sinus can push inward, giving the affected area a concave appearance. Or, the damaged bone might heal as a bony enlargement, creating a cosmetically displeasing hard bump at the injury site. Horses can also experience epistaxis following such trauma.
These obstruct the airways and potentially restrict the nasal passages. They are usually associated with nonodorous drainage and/or facial distortion.
Other possible issues involve benign or malignant growths within the sinuses or fungal infections in a sinus.
Other Facial Findings
Guttural pouch (GP) issues
Guttural pouch mycosis (fungal infection) is particularly dangerous and must be managed as an emergency, says Garcia-Lopez. Here’s why: “Inflammation created by fungal plaques can affect critical cranial nerves within the GP that are involved in the swallowing of food,” he says. “These plaques also may erode the wall of important arteries such as the internal carotid, the external carotid, and maxillary arteries.” Spontaneous bleeding can turn into catastrophic fatal hemorrhage, says Bell.
Treatment includes embolization (creating a permanent blockage using coils or balloons) of the affected artery; once it’s obstructed, the fungal plaque dies off gradually due to a lack of blood supply. Garcia-Lopez says the infection then resolves on its own.
Bell says the guttural pouches are also a common location for Streptococcus equi bacterial infections, known as strangles. “Like the sinuses, the guttural pouches are closed off other than a single drainage point,” he says. “Pus is drained via tubes placed with an endoscope or through surgical removal of hard, pus-containing ‘stones.’ ” He stresses that antibiotics alone usually won’t resolve S. equi infection in the guttural pouch.
S. equi is known to persist in the guttural pouches for long periods, even when not causing clinical disease. Therefore, affected horses can be carriers of the disease and infect others.
A horse might drool for many reasons. “It is important to obtain a complete history, including vaccination history specifically for rabies,” says Garcia-Lopez. “A thorough physical and neurologic examination is conducted, taking proper precautions if the horse’s history is unknown or there is a risk or concern for rabies. Oral, dental, endoscopic, and radiographic examinations help rule in or out causes such as dental disease, a foreign body, or temporohyoid osteoarthropathy (a bony growth disorder of the voice box that causes fusion and fracture of the temporohyoid joint).”
“The physical and oral exams can detect lesions of the mouth from vesicular stomatitis virus … as well as dental disease, obvious foreign bodies such as foxtails or wood splinters, or cancer,” adds Bell. “If the source of drooling isn’t obvious, radiographs of the head and jaw may locate metallic foreign bodies.”
The fatal neurologic disease botulism (which you can vaccinate against) also causes drooling; a veterinarian can confirm diagnosis via serology and a neurologic assessment of the whole horse.
“A key point regarding drooling is to determine if the discharge comes from the mouth or nose,” says Bell. “Choke (esophageal obstruction) in horses is common; saliva will run from the nostrils, which can be mistaken for drool from the mouth.”
Nasolacrimal duct blockage
Blockage of the nasolacrimal duct, which runs through the skull from the corner of the eye to the nostril, is common in horses. Usually veterinarians remedy it by flushing the duct with saline using a nasal cannula placed into the opening (puncta) at the nostril. If this treatment method—along with topical ophthalmic corticosteroid-antibiotic ointment—fails, Bell and Garcia-Lopez say they get a better look at what’s going on inside the head using contrast dye and radiographs, CT scan, or MRI. This helps them determine if a physical obstruction within the sinus or nasal passage is blocking the duct.
“Permanent blockage of a nasolacrimal duct by deformity from increased sinus pressure, a sinus mass or cyst, a tooth root abscess, skull fracture, damage to conjunctiva of the eye, or from previous sinus surgery may respond to a surgical procedure that creates a new drainage duct from the puncta at the inner corner of the eye directly into a sinus,” says Bell.
Bell says this frustrating condition is often associated with trigeminal nerve (which supplies all sensation to the face) issues, though it can also be associated with inflammation, bursitis, and/or pain. Veterinarians diagnose it based on clinical signs, such as vertical headshaking, rubbing the nose on the ground and forelimbs, hypersensitivity to touching the face, and/or increasingly frequent head movements when exposed to sunlight, which occurs in about 65% of cases, he says. Infusing local anesthetic (nerve block) into several locations along the trigeminal nerve can help confirm the diagnosis. A thorough work-up will help your veterinarian determine if the cause is correctable or unknown.
Bell says veterinarians try to treat this condition using medication to alter nerve irritation at the brain level; nose nets for counterirritant therapy; and eye covers and indoor stabling to block UV sunlight. Peripheral electrical nerve stimulation (hyperstimulation via a probe placed under the skin) might reduce the brain’s response to the stimulus and provide short-term intermittent resolution, he adds.
“If medical management fails to work, there are several available surgical procedures,” Bell says, adding that they’re not particularly successful.
The most common cancer in the head is squamous cell carcinoma (SCC), says Bell. “SCC may occur in the sinuses, around or behind the eyes, or in the oral cavity,” he says. “Dental origin tumors are the next most common group of head cancers. Other possible skull tumors include brain tumors, eye tumors, tongue, pharyngeal, and other soft tissue tumors. In general, tumors of the equine head and upper neck are uncommon.”
When SCC does occur, says Garcia-Lopez, it tends to be invasive and associated with a poor prognosis. Veterinarians and researchers have seen an increased incidence of SCCs in horses lacking skin pigmentation, such as Appaloosas and Paints, particularly around the eyes; these are often resolvable, he says.
A horse’s head is a complex and wonderfully evolved structure. You probably spend a lot of time petting and grooming this area. Be on the lookout for telltale signs of brewing trouble in any area of the head, and contact your veterinarian with concerns because early diagnosis is key to a successful resolution.
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