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updated 8/7/2015 11:15:32 AM ET 2015-08-07T15:15:32

An auto mechanic in Boston survived the removal of a rare "giant aneurysm" from his brain, according to a new report of the man's case.

Aneurysms larger than 2.5 centimeters (1 inch) are rare, and are called "giant aneurysms," but the size of this man's aneurysm was a whopping 7 centimeters (2.75 inches), which is extremely unusual, according to the report.

"A 7-centimeter aneurysm is mega-giant — it's about the size of a good-sized peach," said Dr. Nirav Patel, the neurosurgeon at Boston Medical Center who performed the man's surgery and co-authored the case report, published today (Aug. 5) in The New England Journal of Medicine.

"This is the largest reported aneurysm of the anterior communicating artery," Patel said, referring to the blood vessel that connects two major arteries on opposite sides of the brain. He said he once operated on an 8-cm (3 inches) aneurysm, but it was in a different location. [ 10 Things You Didn't Know About the Brain ]

An aneurysm is a weakening in the wall of an artery, Patel said, and in this Massachusetts man's case, the ballooning blood vessel formed a gigantic mass in his brain's frontal lobe, which is just above the eyes and forehead.

The 55-year-old man came to the doctor in January 2013 due to worsening vision in his right eye, Patel said.

Besides the man's struggles with his eyesight, his family was also concerned about personality changes they had noticed in him. Over the prior three years, he had become increasingly forgetful; he would blurt out inappropriate remarks in social situations, and he seemed to lack insight.

His family thought he might be abusing alcohol because he behaved the way someone would if he had a few drinks in him. But his symptoms are common for a person who is having frontal-lobe problems, Patel said.

Complex surgery

A CT scan and MRI of the man's brain revealed the giant aneurysm in his frontal lobe, the most common location for aneurysms to develop.

An aneurysm in this location squishes the brain, and can lower a person's ability to filter their behavior, Patel said. In the man's case, it led him to act on his impulses, and could also have been responsible for his lack of insight, as he truly wasn't aware of his personality changes, he said.

Patel said he suspects the man's aneurysm had been growing in his brain for more than 10 years.

The mechanic also had several risk factors for aneurysms. His sister had died of a brain aneurysm, and about 20 percent of people with brain aneurysms have a first-degree relative who also had the condition. He was also a smoker and had high blood pressure, which are two factors linked with aneurysms.

Giant aneurysms are much rarer than smaller ones, but because of their large size, they are more likely to rupture.

Once an aneurysm reaches 2.5 cm (the threshold at which it is considered "giant"), a person's chances of dying in the next five years is at least 40 percent, Patel said.

"Based on the size of this man's aneurysm alone, if it was not treated, it would have taken his life," Patel told Live Science. Given its extraordinary size, it's unclear why his aneurysm did not rupture, he added.

The man underwent a complex brain surgery that lasted 23 hours. Patel and his surgical team removed the mass from inside the aneurysm and repaired the vessel, so that it would never rupture. This procedure essentially removed the aneurysm, he said.

After the surgery, the man's symptoms improved dramatically, and he was able to go back to work three months later. His memory returned, and his personality showed improvement, Patel said.

When Patel last saw the man, earlier this year at his two-year follow-up exam, he was doing very well. He had quit smoking and was taking his blood-pressure medication. However, he still had some short-term memory problems.

A brain scan taken in 2015 showed the aneurysm had not returned.

© 2012 LiveScience.com. All rights reserved.

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