Doctors at Northwestern Memorial Hospital said they removed part of the 52-year-old's skull -- a 4-inch by 8-inch section -- to help relieve the pressure on his brain following swelling caused by a stroke. The senator checked himself into Lake Forest Hospital on Saturday after having headaches and dizziness. He was transferred to Northwestern Memorial Hospital on Sunday. Tests showed he had an ischemic stroke on the right side of his brain. He remains in intensive care.
"What that means is that it will affect his ability to move his left arm, possibly his left leg," Doctor Richard Fessler, neurosurgeon at Northwestern Memorial Hospital, said. Doctors do not believe Kirk's ability to speak or understand was affected.
"Most of our cognitive functions- our ability to speak, understand, have higher thinking on the left side of the brain. I believe when we are all through this, the left side of the brain will be fine," Dr. Fessler said. "We're very hopeful when we get through all of those functions will be intact."
Dr. Fessler said they decided to do surgery when Kirk started showing signs of being "less responsive" Sunday.
Kirk's recovery will be weeks or even months, according to Dr. Fessler. "It will not be days," he said. "When we take him off sedation, he follows commands and seems to know who's around him. That's very good."
"I think his prospects for a full mental recovery are very good. I think his prospects for a full physical recovery, particularly on his left side of his body are not great," Dr. Fessler said. "I think the use of his left arm is going to be very difficult. I'm hopeful for the use of his left leg."
Richard Goldberg, who works for Kirk, read a statement from the family, "We are very grateful for the excellent treatment and care provided by the doctors and their medical teams... we are equally grateful for the loving support of our family and friends."
"We are confident that the fighter in him will prevail," Goldberg read.
Earlier this month, Kirk was in Poland with Chicago congressman Mike Quigley.
"Hard to a imagine a fitter, healthier U.S. Senator," Quigley told ABC7. "I just travelled to Poland with Sen. Kirk and he seemed a picture of fitness and vitality."
In Washington, Ill. Democrat Dick Durbin -- unaware of Kirk's stroke until Monday morning -- led the bipartisan well wishes for the moderate Republican.
"He has a tough, steep hill ahead of him, but he is up to the task. If the encouragement from a Democrat as well as many Republicans is what is needed, he has it," Durbin said.
"I wish him a full and speedy recovery and look forward to his return to his work here in the Senate as soon as possible," said Sen. Mitch McConnell, (R) Senate minority leader.
Public officials in Illinois also expressed concern and support for Sen. Kirk.
"Like anyone who knows Sen. Kirk, I am stunned and saddened to hear about his recent stroke. But if there is one thing I have learned about Mark over the years, it's that he is a fighter and relentless in his efforts to accomplish a goal. Those attributes will serve him well in working toward a rapid recovery. My thoughts and prayers are with him," Illinois Comptroller Judy Baar Topinka said Monday.
Not even the White House was aware until Monday morning that Illinois' junior senator had a serious medical problem.
"We're obviously concerned about his condition but wish him a speedy recovery," said White House press secretary Jay Carney.
The Republican was elected to represent Illinois on the U.S. Senate in November 2010, winning a special election for President Barack Obama's vacated seat. His regular, six-year term started in 2011.
He served five terms in the United States House of Representatives for the Illinois 10th District before being elected the U.S. Senate.
Monday is the first day back after a three-week recess for the U.S. Senate. Kirk will miss the votes scheduled for the afternoon.
He currently lives in Highland Park, IL.
There is no provision to replace Kirk in the United States Senate as he convalesces.
Information on strokes provided by the American Stroke Association:
Ischemic strokes accounts for 87 percent of all stroke cases. The other type of stroke is hemorrhagic (bleeding), as well as TIAs (mini-strokes).
Warning signs/symptoms of an ischemic stroke:
- Sudden numbness or weakness of the face, arm or leg, especially on one side of the body
- Sudden confusion, trouble speaking or understanding
- Sudden trouble seeing in one or both eyes
- Sudden trouble walking, dizziness, loss of balance or coordination
- Sudden, severe headache with no known cause
Ischemic stroke information and resources:
Life after stroke:
American Stroke Association: www.strokeassociation.org
Stroke Survivors Empowering Each Other (SSEEO): www.sseeo.org