WASHINGTON - U.S. Sen. Mark Kirk, R-Ill., one of the younger and most active senators in terms of scheduling and travel, suffered a stroke this weekend and was recovering Monday after undergoing surgery at a Chicago hospital.

While Kirk, 52, may encounter some lingering effects from the stroke -- likely involving his left-side limbs and partial facial paralysis -- doctors told reporters Monday that his longer-term prognosis is good, given the nature of the stroke, his age and otherwise generally good health.

According to a statement issued by his staff, Kirk had checked himself into Lake Forest Hospital north of Chicago on Saturday, where doctors discovered a "carotid artery dissection" on the right side of his neck. Such an arterial tear can divert blood from the brain, physicians say.

After Kirk was transferred to Northwestern Memorial Hospital in Chicago, further medical tests showed that the senator "had suffered an ischemic stroke." Early Monday, he "underwent surgery to relieve swelling around his brain stemming from the stroke," the statement said. A small part of the skull was removed to relieve pressure.

Describing that surgery as "successful," the statement from Kirk's office said physicians gave a positive prognosis. "Due to his young age, good health and the nature of the stroke, doctors are very confident in the senator's recovery over the weeks ahead," the statement said.

The Chicago Tribune quoted the neurosurgeon who performed the surgery, Dr. Richard Fessler, as saying that Kirk tolerated the surgery well but that there may be lingering effects from the stroke. "It will affect his ability to move his left arm, possibly his left leg and possibly involve some facial paralysis," Fessler said. However, the surgeon said he hoped that some of those left-side impairments may be eased once Kirk recovers.

The Tribune went on to quote Fessler as describing the chances for a full mental recovery as "good" -- but "not great" for a full physical recovery.

The Chicago Sun-Times quoted Fessler as saying it was fortunate that the stroke involved only the right side of the brain -- affecting Kirk's ability to move his left arm and possibly his left leg -- and not the brain's left side, which might have had an impact on the senator's speech functions.

The National Journal quoted Fessler as cautioning that Kirk's recovery will take a while. "It's not going to be days," he said.

Kirk, a Naval reserve intelligence commander who has served stints in Afghanistan and traveled in the past year to Libya and Somalia, spent much of the last week at appearances in southern and central Illinois. He had returned to Chicago on Friday to attend a staffer's goodbye party.

Many of Kirk's congressional colleagues said they were startled by the news of the stroke. Illinois' senior senator, Dick Durbin, D-Ill., said he was "stunned to learn that Mark suffered a stroke. He is young and in good physical condition and I have no doubt he will make a speedy recovery."

While representing different political parties, Durbin and Kirk have forged a working relationship in the Senate, and they co-host constituent coffees for Illinois visitors on Capitol Hill nearly every week that Congress is in session. Durbin said Monday that he had "reached out to [Kirk's] staff and offered to do anything I can to help with his Senate duties. Loretta and I will keep Mark and his family in our prayers."

One of Kirk's closest friends in the Senate is Sen. Roy Blunt, R-Mo., who underwent successful cardiac stent surgery on Jan. 12. Blunt told the Beacon on Monday that he is feeling well and is back at full speed.

"Mark [Kirk] is one of my closest friends in the Senate and he's been a valued colleague of mine for many years, including as one of my deputies when I was the whip in the House," Blunt said in a statement.

"He's a strong advocate for his views, he works hard, and he's a great neighbor. Missouri, along with Illinois and the rest of the nation, benefits greatly from Mark Kirk's leadership. I'm encouraged by his doctor's comments and wish him a very speedy recovery."

Blunt and many other House members from Missouri and Illinois got to know Kirk during his decade in the U.S. House. He was first elected to the House in 2000 from a suburban Chicago district, which he represented when he won the 2010 U.S. Senate race against Democrat Alexi Giannoulias. Kirk now occupies the Senate seat once held by President Barack Obama.

Sen. Claire McCaskill, D-Mo., said in a statement Monday that she was "keeping Mark and his family in my thoughts and prayers and wishing him a full and speedy recovery."

There was no word Monday on how long Kirk is likely to be away from his Senate duties. Illinois and Missouri lawmakers expressed hope that Kirk will recover fully.

U.S. Rep. John Shimkus, R-Collinsville, said in a statement that his "prayers are with Mark during this very crucial time. As his doctor's stated, every stroke is serious. I am hopeful that Mark will make a full recovery as quickly as possible." U.S. Rep. Jerry Costello, D-Belleville, tweeted that he was "wishing my friend and colleague Sen. Mark Kirk a speedy and full recovery. He is in our thoughts and prayers."

Rep. Todd Akin, R-Wildwood, said through a spokesman that he "sends very best wishes for a speedy recovery and hope to see [Kirk] back to work in the Senate shortly."