Joe Biden almost died after suffering an aneurysm while serving in the Senate, but the surgeon who operated on his brain says that the incident shouldn't hold him back in his pursuit of the presidency.

Dr. Neal Kassell, the renowned neurosurgeon who operated on Biden, said he’s confident that Biden is “totally in the clear,” and joked that he believed the surgery had even “made him better than how he was.”

“Joe Biden of all of the politicians in Washington is the only one that I’m certain has a brain, because I have seen it,” Kassell said. “That’s more than I can say about all the other candidates or the incumbents.”

Apart from Kassell's endorsement of his brain health, little has been publicly disclosed about Biden’s overall health since 2008, when he released medical records as a vice presidential candidate. Biden would be 78 on Inauguration Day, and he still calls up Kassell every year on the anniversary of his surgery.

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At the time of Biden’s brush with death in 1988, his wife, Jill Biden, feared that he would never be the same. In a forthcoming autobiography, “Where the Light Enters," Jill recounts Joe's doctor telling the family that there was a significant chance he’d have permanent neurological damage, particularly after he suffered a second aneurysm, a condition in which an artery becomes weak and bulges out.

"Our doctor told us there was a 50-50 chance Joe wouldn't survive surgery," she wrote. "He also said that it was even more likely that Joe would have permanent brain damage if he survived. And if any part of his brain would be adversely affected, it would be the area that governed speech."

Initially, Joe Biden suffered an aneurysm that burst and required him to undergo emergency surgery. He was so close to death that a priest was preparing to administer the Catholic sacrament of last rites. A few months later, surgeons clipped a second aneurysm before it burst, after discovering it during a routine screening.

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Despite a “messy recovery,” as described by his wife, Biden left the operating room with his “brain function intact.”

He took a seven-month leave from the Senate following the surgery, and has described it in blunt terms, saying, “they literally had to take the top of my head off.”

Not everyone is as fortunate after an aneurysm as Biden was: 30,000 people have aneurysms that rupture every year, and about 40 percent of those cases are fatal. Of those who survive, 66 percent have a neurological deficit.

The last time Biden disclosed information about his health was in 2008 when Dr. Matthew Parker, a physician the Obama campaign selected when Biden was the running mate, spoke to the press. Biden’s actual doctor, John Eisold, the physician who attended to Biden and the rest of Congress, was not the one to present the medical records.

The 2008 disclosure revealed that Biden had an irregular heartbeat that was attributed to sleep apnea, and that he had his gallbladder removed in 2003. He continued to suffer from asthma and allergies, conditions which began in childhood, and took aspirin and the prescription drug Zocor to lower cholesterol. Doctors removed a benign polyp during a colonoscopy in 1996, and he had been diagnosed with an enlarged prostate, for which he took Flomax.

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Parker said he didn’t know whether Biden had more aneurysms, and said “everything that could be done is being done.”

From the information revealed, it was not clear how often Biden has been screened for aneurysms, and there wasn't any other information provided when he was vice president. In contrast, records show that Barack Obama had at least four medical checkups during his presidency.

No law requires presidents, vice presidents, or candidates to have a medical checkup or to disclose what comes of it.

Dr. Babu Welch, a neurological surgeon with University of Texas-Southwestern’s O’Donnell Brain Institute, said that people who have had one aneurysm can always have another. People are supposed to undergo regular screenings shortly after they have an aneurysm, but then can space them out further as time goes on, he said.

Dr. Gavin Britz, director of the Houston Methodist Neurological Institute, said his research has revealed that people have a decrease in life expectancy after an aneurysm. The key, he said, is to make sure to catch them before they rupture.

Those close to Biden say they have no concerns about his health as he enters yet another White House run. A former senior aide said Biden remains a “picture of health.”

“I don’t think there’s anything to worry about, his fitness is like someone 10 years younger than him. This is a man who enjoys running for president,” the former aide told the Washington Examiner. “His health has never been a concern for anyone who knows him or works with him.”

Yet Biden would also be the oldest man to enter the White House should he win in 2020. Speculation about presidential candidates' health is not new: Whispers emerged about Ronald Reagan potentially having Alzheimer’s disease during his reelection campaign in 1984, Sen. John McCain faced scrutiny over his healthcare records when he ran for president against Barack Obama, and Dr. Ronny Jackson found himself in the middle of a tense press conference in January 2018 following his diagnosis that President Trump was in “excellent” physical and cognitive health.

“I don’t think the concerns about Biden’s age are as much about health as it is outlook or perspective. You have to be part of where we’re headed, not where we’re coming from,” Peter Hart, a Democratic pollster, told the Washington Examiner. “Obviously if there’s a health issue, that’s going to be a major factor in the race, but having no health problems is the lowest bar for a candidate to clear.”