Traumatic Brain Injury in Horses

"Head trauma is common in horses, and a number of these cases will present with neurologic signs consistent with brain injury," began Darien Feary, BVSc, MS, Dipl. ACVIM, ACVECC, a lecturer in equine medicine with the University of Sydney, Australia. She discussed management of these injuries at the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla.

Due to limited research on equine brain injury, most equine recommendations come from human research, she reported.

The two most common types of equine head trauma resulting in neurologic dysfunction are injury to the frontal/parietal brain from kicks or head-on collisions and poll trauma from flipping over backward, she said. These injuries are not always associated with fractures.

Frontal trauma can result in lacerations or contusions of the cerebral cortex. Neurologic signs can include contralateral (in the opposite eye) blindness, depressed mentation (mentality), compulsive wandering, and generalized seizures.

Poll trauma tends to result in the most severe brain injuries. "Young horses are particularly susceptible to this because they tend to flip over on their heads when they don't want to do something, and the skull bones in this area don't fuse until they're three to four years old," Feary noted. Brainstem and blood vessel damage with this injury can cause head-tilt, nystagmus (involuntary, rapid, rhythmic movement of the eyeball), depressed mentation, tetraparesis (weakness of the extremities), facial nerve paralysis, and bleeding into the guttural pouches.

Brain injury takes two forms--primary and secondary. Primary injury is immediate, direct, mechanical, or structural injury occurring at impact, such as concussions, lacerations, edema (fluid swelling), or hemorrhage. Secondary injury encompasses "the cascade of local, then global, cellular and neurochemical alterations that occur in minutes to days after the initial injury and lead to progressive axonal (nerve body) degeneration and cell death," Feary explained. "In contrast to primary injury, which the clinician has no or minimal control over, the deleterious effects of secondary injury may be attenuated with prompt and appropriate therapeutic intervention."


"The management of recumbent, neurologic equine patients is particularly challenging and labor-intensive, often limiting treatment options and duration," she said. "As a result, the management of severe brain injury in horses is anecdotally reputed to be intensive, expensive, and associated with a guarded to grave prognosis." However, advanced monitoring tools and treatment options available today might improve the success rates with these cases, she noted.

The main goals of therapy are to control intracranial (inside the skull) pressure, keeping it below 20 mm Hg; support cerebral perfusion (blood vessel pressure) at more than 60 mm Hg; minimize secondary injury; and treat any concurrent injuries or diseases.

Systemic conditions that can contribute to secondary brain injury include hypotension (low blood pressure) and hypoxemia (low oxygen content in the bloodstream), and to a lesser extent hypoglycemia/hyperglycemia (low/high blood sugar), acidemia (overly acidic blood), and systemic inflammatory response syndrome. Thus, management also will try to prevent or correct these issues.

Fluid therapy usually consists of isotonic or hypertonic fluids and colloids to correct electrolyte, glucose, and acid-base abnormalities. Hyperosmolar therapy, used to pull fluid swelling out of brain tissues, might also be used; mannitol and hypertonic saline are options for this.

Additional management measures might include inhaled oxygen therapy, non-steroidal anti-inflammatory medication, antioxidant therapy, anti-seizure medication in seizuring horses, thiamine (vitamin B1) supplementation, maintenance of normal body temperature (i.e., cooling horses with fevers), and elevation of the head by 10-30°.

Brain Injury Study

Feary described a retrospective study of 34 horses treated for primary brain injury at the University of California, Davis, between 1994 and 2004. Poll injury was the most common, and 62% of the horses survived. Factors decreasing survival rates included higher packed cell volume (the portion of blood occupied by red blood cells, 40% vs. 33%), recumbency for more than four hours (18 times less likely to survive), and skull base fractures (7.5 times less likely to survive).

"Survival rate in this study was higher than other previously reported studies in horses and widespread anecdotal belief; perhaps this is a reflection of the significant advances made in the equine veterinary profession through all levels," she concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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