CHICAGO (CBS) — Doctors on Tuesday reattached a portion of Sen. Mark Kirk’s skull, which had been removed to help relieve pressure on his brain after he suffered a stroke.

“The swelling in Sen. Kirk’s brain has subsided and this morning we were able to reattach the portion of his skull that had been removed following his stroke. This is an important milestone in his recovery and a step toward the next phase, rehabilitation. He remains in good condition,” said Dr. Richard Fessler, a neurosurgeon at Northwestern Memorial Hospital.

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The senator suffered an ischemic stroke the weekend of Jan. 21. He underwent surgery that weekend to remove a large section of his skull in order to reduce swelling on the right side of his brain.

A few days after the initial surgery, doctors performed another procedure to remove two small pieces of brain tissue that had been rendered non-functional by the stroke.

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Fessler has said Kirk will have a long road to recovery and, although he is expected to make a full mental recovery, he’s likely to suffer long-term problems using his left arm and, possibly, his left leg. He might also suffer some partial facial paralysis.

Doctors said if the stroke had occurred on the left side of Kirk’s brain, the effects could have been more severe, because the left side of the brain controls most cognitive functions.

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For Kirk, rehabilitation will mean restoring as much function as possible on the left side of his body and learning to live with whatever permanent limitations that might result from the stroke.