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.
Mild symptoms include headache, confusion, lightheadedness, dizziness, blurred vision and temporary behavioral changes, while moderate or severe cases may involve convulsions and seizures.
Repair technique: I-shaped skin incision exposes multiple-impact skull fractures.
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.