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.
This article continues in the June 2020 issue of The Horse: Your Guide to Equine Health Care. Subscribe now and get an immediate download of this issue, including this in-depth article on issues that can affect your horse’s head structures, from his lymph nodes to his nostrils.