People rarely survive gunshot wounds to the head, but so far Arizona Rep. Gabrielle Giffords, shot point-blank in the back of her head on Saturday, has held on. Monday morning her doctors indicated they were "slightly more optimistic" about her prognosis. In the wake of this brutal tragedy it is worth recognizing the series of highly fortunate events that led to Giffords's continued survival.

The most important predictors for how well a victim will recover from a gunshot wound to the head are the type of bullet and its travel path once inside the brain, and Giffords was fortunate on both counts, says Keith Black, chairman and professor of neurosurgery at Cedars–Sinai Medical Center in Los Angeles. The bullet, reportedly fired from a Glock 19 9-millimeter, semiautomatic handgun, entered the left side of the back of her head and traveled through her brain, exiting through her forehead. This "through and through" path indicates that the bullet was probably not of the variety designed to expand or break into smaller fragments once inside the body, which would have caused a much severer injury. Further, the wound would have been much more damaging had the bullet ricocheted off the inside of her skull or if it had remained lodged in her brain matter where it could "migrate around" and cause additional harm, Black says.

As the projectile traveled forward, it remained in her brain's left hemisphere, avoiding crossing through the middle to the other side, which, according to Black, could have caused catastrophic injury. The bullet's trajectory was also high enough to apparently avoid certain crucial left-hemisphere structures, including areas responsible for language processing—a notion reinforced by reports that Giffords has been responsive to commands.

Immediately following the injury, it was not only the quality but also the speed of the care Giffords received that probably saved her life. "As we say in neurosurgery," Black says, "time is brain." Crucially, one of Giffords's aides positioned her so that blood did not impede her breathing. Subsequent transport to the level 1 trauma center at the University of Arizona’s University Medical Center in Tucson, and the care given once she arrived, was very rapid. Reportedly, only 38 minutes transpired between the time she was injured and when she entered surgery.

That the facility was fully equipped to handle such an traumatic injury was key. "It was very important that there was no delay," once she arrived at the hospital, Black says, adding, “If she would have had to be transferred to another facility, her prognosis probably would not have been as good"—a fact, he notes, that speaks to the need for more level 1 centers across the country.

Once in surgery, neurosurgeons removed bone fragments, worked to stop the bleeding, and then performed an operation called a decompressive hemicraniotomy. The procedure, which has become popular in the past decade or so, especially in the context of battlefield brain injuries, entails the removal of a portion of the skull to allow room for the brain to swell. Brain swelling creates increased pressure inside the cranium, and if part of the bone is not removed the pressure disrupts a vital differential between blood pressure and the pressure in the brain. When it comes to swelling, Black explains, "minutes count," and the fact that the pressure in her brain was relieved so quickly is essential to her relatively positive prognosis.

Brain injuries are complex, and it is too early to know definitively the extent to which Giffords will ultimately be set back or if she can make a full recovery. But the next few days will be very critical, Black says, as potentially dangerous brain swelling "tends to maximize on the third day of injury," which would be Tuesday. After that point, doctors can expect her condition to begin to stabilize.