Sen. Mark Kirk, R-Ill., likely faces permanent physical damage and a long-term cognitive recovery after successful surgery for a stroke, doctors said Monday.
Neurosurgeons at Northwestern Memorial Hospital in Chicago said parts of Kirk's brain are permanently damaged.
"The prospects for his full physical recovery, particularly on the left side of his body, are not great," said Dr. Richard Fessler, a neurosurgeon at Northwestern Memorial.
The stroke may also result in "some facial paralysis," Fessler added, with Kirk maybe recovering use of his left leg, but "the use of his left arm is going to be very difficult."
Fessler said that Kirk's "prospects for a full mental recovery are pretty good."
"Senator Kirk's job is cerebral, and I believe the functions required to do his job are going to be fine," he added.
Kirk, 52, was elected in 2010 to fill the seat previously held by President Obama. He is divorced and does not have children. His office announced his surgery early on Monday in a statement that said he had a stroke on Saturday and underwent surgery early on Monday to relieve pressure on his brain.
Fessler warned that recovery would be difficult. "It's not going to be days," Fessler said.
In a statement earlier, the senator's office said: "On Saturday, Senator Kirk checked himself into Lake Forest Hospital, where doctors discovered a carotid artery dissection in the right side of his neck. He was transferred to Northwestern Memorial Hospital in Chicago, where further tests revealed that he had suffered an ischemic stroke. Early this morning, the senator underwent surgery to relieve swelling around his brain stemming from the stroke."
Ischemic strokes are the most common type of stroke and affect people of all ages.
Doctors said Kirk began to "deteriorate neurologically" Sunday evening, leading to the surgery to relieve brain swelling. Surgeons said they removed a "four-by-eight inch piece of skull" to alleviate pressure.
Kirk's stroke recalls the aneurysm suffered in 2006 by Sen. Tim Johnson, D-S.D. Johnson, whose seat allowed Democrats to retain a slim Senate majority at the time, has partly recovered physically since. Johnson, now chairman of the Senate Banking Committee, often uses a wheelchair and his speech remains impaired, though he has been described as making a full mental recovery. Kirk's stroke was announced day after Rep. Gabby Giffords, D-Ariz., who was shot in the head last year and continues to recover, announced she was stepping down from her seat.