Doctors gave few details about the surgery, and did not say how much was removed. The procedure lasted about 31/2 hours, and when he emerged, a family spokeswoman said he told his wife, Vicki, that he felt “like a million bucks.”

The sole surviving son of America’s most glamorous and tragic political family was diagnosed last month with a malignant glioma, an often lethal type of brain tumor discovered in about 9,000 Americans a year.

Details about Kennedy’s exact type of tumor have not been disclosed, but some cancer specialists have said it is a glioblastoma multiforme — an especially deadly and tough-to-remove type — because other kinds are more common in younger people.

Cutting a tumor down to size — or “debulking” it — is extremely delicate because of the risk of harming healthy brain tissue that governs movement and speech. But Friedman, who is the top neurosurgeon at Duke and an internationally known tumor surgeon, said Kennedy should not experience any permanent neurological effects.

Median survival for glioblastomas is 12 to 15 months, but the range is wide, said Dr. Mark Gilbert, a brain tumor expert at the University of Texas M.D. Anderson Cancer Center in Houston.

The outlook for patients with malignant gliomas is poor, and depends on what type of glioma a patient has. Median survival for patients with moderately severe ones is three to five years, and less than a year for those with the most severe type.

Doctors have not revealed Kennedy’s treatment plan, but typical radiation treatment is five days a week for a month, using 3D imaging techniques that narrowly deliver the beams to the tumor, affecting as little surrounding tissue as possible.

Kennedy also likely will receive the chemotherapy drug Temodar during and after radiation. It can cause typical chemo side effects — nausea, vomiting and fatigue — but treatments are much better for these than even a few years ago, doctors stressed.

He also may be treated with Avastin, a newer targeted drug to deprive the tumor of its blood supply, though this is still experimental as initial treatment, rather than after patients have relapsed.

Monday’s operation “spells nothing but hope,” Dr. John Sampson, associate deputy director of Duke’s brain tumor center, said from Chicago, where he was attending a conference of 30,000 cancer specialists.

“What we’re seeing with the surgery and this conference is that there’s hope for patients with this kind of cancer.”