Strokes such as the one that struck Sen. Mark Kirk are rare but not unheard of for men in their 50s who are generally healthy and fit, experts said this week.
"It's often a mystery why it happens, but we see it, and we see it in people without the usual risk factors," said Dr. James Brorson, medical director of the stroke center at the University of Chicago Medical Center.
The Illinois Republican suffered an ischemic stroke, in which an arterial blockage prevents blood flow to the brain.
Doctors said the cause of his stroke was unclear, but they found that Kirk, 52, had a carotid artery dissection, or a tear in one of the blood vessels that run on either side of the neck into the brain.
A stroke can occur if blood clots that form to heal the wound break off and lodge in a smaller artery in the brain, or if the carotid artery itself becomes blocked. Patients typically are treated with blood thinners to prevent the formation of clots.
"In everyday life, blood clotting is beneficial," said Jim Baranski, chief executive officer of the National Stroke Association. "When you are bleeding from a wound, blood clots work to slow and eventually stop the bleeding. In the case of stroke, however, blood clots are dangerous because they can block arteries and cut off blood flow."
As blood flow to the brain diminishes, the tissues of the brain can swell. Damage caused by strokes varies, depending on the size and the location of the stroke, but surgery to relieve pressure indicates a major event.
The fact that neurosurgeons at Northwestern Memorial Hospital removed a 4-by-8-inch section of Kirk's skull to ease brain swelling "suggests that there was a lot of damage, unfortunately," said Brorson. "That's unequivocal."
Kirk's neurosurgeon at Northwestern Memorial, Dr. Richard Fessler, said Kirk's right carotid artery was permanently damaged, and other blood vessels will have to take over its functions.
Any number of events can cause a carotid artery dissection, including extending the neck in one position for a long time, such as when painting a ceiling, or experiencing abrupt neck motion in a car accident, Brorson said.
Dr. Jay Alexander, a friend of Kirk's and an internal medicine doctor at Northwestern Lake Forest Hospital, said Kirk did not report any activities that would have caused neck trauma and had not done anything out of the ordinary.
Strokes kill more than 133,000 people annually and leave many more with serious and long-term disabilities, according to the National Stroke Association.
Two million brain cells die every minute during a stroke, increasing the risk of permanent brain damage, disability or death. Slurred speech, headaches, one-sided face drooping or limb weakness all can be signs of a stroke, according to the association.
People who think they are having a stroke should dial 911 immediately. Survival can often come down to getting immediate medical attention.