The condition for which Senator John McCain had surgery on Friday may be more serious than initial descriptions have implied, and it may delay his return to Washington by at least a week or two, medical experts said on Sunday.
The Senate majority leader, Mitch McConnell, has already announced that votes on a bill to dismantle the Affordable Care Act will not begin until Mr. McCain’s return. A statement released by Mr. McCain’s office on Saturday had suggested that he would be in Arizona recovering for just this week, but neurosurgeons interviewed said the typical recovery period could be longer.
The statement from Mr. McCain’s office said a two-inch blood clot was removed from “above his left eye” during a “minimally invasive craniotomy with an eyebrow incision” at the Mayo Clinic Hospital in Phoenix, “following a routine annual physical.” Surgeons there are not conducting interviews, and Mr. McCain’s communications director, Julie Tarallo, said no further information was available.
A craniotomy is an opening of the skull, and an eyebrow incision would be used to reach a clot in or near the left frontal lobes of the brain, neurosurgeons who were not involved in Mr. McCain’s care said.
“Usually, a blood clot in this area would be a very concerning issue,” said Dr. Nrupen Baxi, an assistant professor of neurosurgery at the Albert Einstein College of Medicine in New York City.
He added, “The recovery time from a craniotomy is usually a few weeks — at least a week or two.”
A statement from the Mayo Clinic Hospital said that the senator was recovering well and in good spirits at home, and that tissue pathology reports would come back in several days.
But many questions have been left unanswered, including whether Mr. McCain had symptoms that prompted doctors to look for the clot. In June, his somewhat confused questioning of James B. Comey, the former F.B.I. director, led to concerns about his mental status, which he later jokingly dismissed by saying he had stayed up too late watching baseball the night before.
“Usually, a blood clot like this is discovered when patients have symptoms, whether it’s a seizure or headaches or weakness or speech difficulties,” Dr. Baxi said. “Generally, it’s not found on a routine physical because doctors would not know to look for it.”
The cause of the clot has not been disclosed. The possibilities include a fall or a blow to the head, a stroke or certain brain changes associated with aging. Mr. McCain is 80.