A boy in Idaho who was recently in a high-speed car crash has survived a rare injury called an "internal decapitation," which is typically fatal, and is more common in children than in adults.

The 4-year-old boy, named Killian, and his mother, were driving home from a birthday party when a hailstorm hit, and their car skidded into oncoming traffic and collided with another car, CBS affiliate KBOI-TV reported. During the crash, the ligaments in Killian's neck that attach his skull to his spine were severed, which is referred to as internal decapitation. (The word "decapitation" is a bit of a misnomer, because the head is still attached to the body.)

This type of injury has a high fatality rate, said Dr. Toba Niazi, a pediatric neurosurgeon at Nicklaus Children's Hospital in Miami, who was not involved in Killian's treatment. When the ligaments become severed in such injuries, the head might move around more than it should. Consequently, if the injury isn't recognized early, there can be damage to the lower brain stem, Niazi said. The brain stem is a vital area of the brain that controls breathing.

The exact fatality rate in this type of injury is not known, said Niazi, noting that people who die in car crashes don't always undergo an autopsy to determine whether they had this injury. But a 2005 study of internal-decapitation injuries at a hospital in Philadelphia found that, over a 17-year period, 16 children with the injury were seen at the hospital, and only five of those children (31 percent) survived. [16 Oddest Medical Cases]

Neck X-ray image National Institutes of Health

The injury is known in medical terms as atlanto-occipital dislocation (the "atlas" is the name of the topmost vertebral bone of the spine; the "occipital" bone forms the lower part of the back of the skull). The injury is three times more common in children than in adults, according to a 2015 review study. This is partly because, compared to adults, children's heads are big for their body size, Niazi said. "It makes children more prone to these types of injuries because of the sheer weight of their head" versus the rest of their body, Niazi said.

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In addition, children's ligaments are more lax than they are in adults, Niazi said, which may also make it more likely that children will experience this injury. (Ligaments connect bones to other bones, and can heal if they are torn, but do so slowly.)

To increase the chances of survival, it is critical to immobilize the head and neck, Niazi said. In the boy's case, a good Samarian arrived on the scene of the accident and held him upright, keeping his head steady until paramedics arrived, the New York Times said.

Treatment of the injury always involves immobilizing the area, Niazi said. This is sometimes done with a device called a halo brace, which involves attaching a circle-shaped brace to the skull with pins. But this method is not always effective at stabilizing the area, Niazi said.

So instead, Niazi recommends surgery, during which rods, wires or screws are used to repair the connection between the skull and the spine.

But Killian has had neither a halo device nor surgery, and instead has just a hard collar around his neck. I was surprised to see this kid was just in a collar," Niazi said, looking at a published picture of the boy.

The 2015 review study noted that internal decapitation "is an essentially ligamentous injury and, as such, is unlikely to spontaneously heal well over time, even after prolonged external immobilization."

However, the injury is "increasingly recognized as a potentially survivable injury," because there is more awareness about it, and because patients are being managed better before they arrive at the hospital, the researchers wrote in their paper.

According to a fundraising website for the family's medical expenses, "Killian's neurosurgeon is pushing for just trying the collars. ... By not fusing the spine they are working outside the box so to speak. Anything you read will say to fuse [the skull with the spine using surgery]. But his neurosurgeon has been 3 for 3 in just wearing the collar."

To reduce the risk of head injuries among children who are in car accidents, it's important to secure them safely while they are riding in a car. This type of injury "underscores the importance of why children really need to be restrained appropriately," Niazi said.

Toddlers and preschoolers can ride in a forward-facing car seat with a five-point seatbelt harness, and children under age 2 should be in a car seat that's facing the rear of the car, according to the American Academy of Pediatrics.

Original article on Live Science.