Helping horses survive traumatic brain injury

It's not uncommon, either in horses or humans.

In both cases, traumatic brain injury (TBI) usually results from an accidental blow to the head, although it may occur even without impact through any violent shaking that tears brain tissue and damages neural pathways.

Thousands of U.S. troops in Iraq and Afghanistan have suffered TBI, and U.S. physicians treat more than a million people a year for it.

Repair technique: I-shaped skin incision exposes multiple-impact skull fractures.

Mild symptoms include headache, confusion, lightheadedness, dizziness, blurred vision and temporary behavioral changes, while moderate or severe cases may involve convulsions and seizures.

Darien Feary, BVSc, MS, Dipl. ACVIM, Dipl. ACVECC, a former fellow in equine emergency critical care at the University of California-Davis and now on the clinical faculty at the University of Sydney in Australia, discussed TBI in horses, including its diagnosis, treatment and prognosis, at the American Association of Equine Practitioners meeting in Orlando in December.

More often seen in young horses, TBI results from "sustaining an injury to the poll subsequent to rearing and falling over backwards on the dorsum during halter training or restraint," Feary says, or from "head injury while struggling from entrapment in a fence or subsequent to becoming prone in a stall."

Skull fragments removed to allow evacuation of blood clots and fragments trapped in the sinuses.

Other frequent causes, she says, include running into a tree, struggling during recovery from anesthesia or being kicked by another horse.

On the racetrack, falls or accidents in the starting gate that result in head injury may produce TBI.

Whatever the cause, a chief concern with any trauma that causes frontal or poll injury is possible damage to the central nervous system (CNS).

"Some of the most common activities that can result in a horse flipping over backwards (and possibly causing TBI) include halter training, ear clipping and trailer loading," says Claude Ragle, DVM, Dipl. ACVS, Dipl. ABVP, associate professor of equine surgery at Washington State University College of Veterinary Medicine. "Older horses can develop the habit of flipping over backwards in response to a given stimulus such as tightening of the girth or being cross-tied," Ragle says.

Repair complete: Reconstruction of elevated fracture fragments that are connected using absorbable sutures.

The higher incidence of TBI in young horses that Feary observed has been confirmed by other studies and seems related their greater likelihood to respond to head restraints during early training.

Traumatic head injuries in young horses may be associated with "their lack of experience, and the exuberance of youth," Ragle says.

"Young horses," according to Feary, "also may be more susceptible to fracture of the basilar bones because the suture between the basisphenoid and basioccipital bones remains open until 2 to 5 years of age. In addition, this is the site of insertion of the largest flexor muscle of the neck (rectus capitis ventralis major) that exerts considerable traction forces during head and neck hyperextension at the time of impact."

Closure of incision. These fractures often heal well, with good functional and cosmetic results.

Diagnosis and findings

The occurrence and severity of TBI in horses may be determined through neurologic exam and with radiographs, endoscopy and computed tomography (CT).

Though survey radiographs can be helpful, computed tomography (CT) may be even more useful in detection and precise localization of intracranial structural lesions, to more precisely define the extent of cranial trauma.

Looking inside: Cranial radiograph demonstrating a basilar fracture.

What about MRI? If available, does it enhance the ability to diagnose and to see more subtle brain injuries? "Absolutely, without a doubt," says Gary Magdesian, DVM, Dipl. ACVIM, Dipl. ACVECC, Dipl. ACVCP, associate professor, chief of equine medicine and critical care at the UC-Davis Veterinary Medicine Teaching Hospital and Feary's mentor during her fellowship there.

"CT has markedly improved our detection of fractures and MRI would do the same for soft-tissue injury," says Magdesian.

According to Feary, "findings of clinicopathologic and cerebrospinal fluid analyses may provide additional information."

Of 34 horses with TBI (previously admitted to the UC-Davis teaching hospital), most records showed various neurologic abnormalities, including ataxia, nystagmus, abnormal mentation, abnormal pupil size, symmetry or PLR (pupillary light reflexes), and head tilt.

Several of the horses exhibited recumbency of greater than four hours' duration, epistaxis, facial-nerve paralysis, strablamus and seizures. Fewer showed otorrhea (blood or cerebrospinal fluid), dysphagia or blindness, and were unconscious for some period.

The clinicopathologic variables predominantly seen were moderate neutrophilia and mild lymphopenia; plasma osmolarity of venous blood was reported for 13 of the 34 animals. Horses with higher PCV at the time of hospitalization were less likely to survive.

Defining view: A CT image demonstrates a fracture of the calvarium.

In Feary's study, the dominant injury (15 of 34 horses) was basilar and temporal bone fractures associated with poll impact, as well as bony fractures of the calvarium.

Of the 34 horses, 11 did not have a fracture of the cranium identified by radiography, CT or endoscopy, nor upon postmortem diagnosis. "It should be noted that serious brain injury in no way requires the presence of a fracture, and the presence of a fracture does not necessarily indicate severe brain damage," says Ragle. "The most important indication of the seriousness of head injury is the duration and progression of recumbency and mental stupor."

Though obvious severe head trauma often leads to TBI, and the result is fairly obvious, that is not always the case. "I believe head trauma can be subtle. We often see horses that are mildly depressed or have altered gait or subtle neurologic abnormalities that could be the result of TBI. Many cases are likely missed and heal with time," Magdesian says.

Treatment and prognosis

Treatment primarily involves supportive care, including hyperosmolar therapy, anti-inflammatory drugs, seizure management, antimicrobial agents and possibly surgical decompression.

With recumbent horses, especially those of extensive duration, treatment and care may be difficult, labor-intensive and challenging, with a grave or guarded prognosis. "The inherent limitations and complications of the management of recumbent adult horses include ongoing self-trauma from struggling; decubital ulceration; reduced ability to eat, drink, defecate and urinate; pneumonia, cystitis, GI-tract dysfunction; compartmental and/or ischemic myopathy and neuropathy; plus considerable labor and financial investment," Feary says.

What is most important regarding care and treatment are "excellent supportive care — maintenance of hydration, blood pressure, nutritional needs, nursing care, pain control," says Magdesian.

According to Ragle, skull-base fracture patients are quite unstable. Brain-injured horses should be "placed in a quiet, secluded stall and every phase of care should be performed in an attempt to prevent triggering another traumatic episode," Ragle notes. "Some patients are unable to move about a stall freely without falling and risking further injury."

Depending on the horse and its situation, some form of constraint to alleviate further injury should be considered.

"Injury to the central nervous system (CNS) should always be taken into account after severe traumatic incidents," says K. Feige, DVM at the Clinic of Veterinary Surgery in Zurich, Switzerland, in a paper on traumatic injury to the CNS.

"The objective evaluation of a horse with suspected traumatic CNS injury should include a thorough history, clinical and neurological examination and individually adapted supplementary examinations," Feige suggests.

What is most remarkable in these TBI cases and what equine practitioners should realize, Magdesian points out, is "the degree to which even severely affected horses can normalize or near-normalize in terms of neurologic status. Given time, most improve dramatically, as long as there are no compound or markedly displaced fractures."

Is it true that the more severe the head trauma, the less likely horses are to survive? "In general yes, but even severe cases can come back if they are not in prolonged recumbency," says Magdesian.

Within Feary's population of TBI cases, 62 percent survived to be discharged, and that is from a referral population, likely the most severe end of the spectrum.

"Survival may be even higher in field-treated cases," Magdesian suggests.

Ed Kane is a Seattle author, researcher and consultant in animal nutrition, physiology and veterinary medicine, with a background in horses, pets and livestock.