Independent presidential candidate Robert F. Kennedy Jr. faced a daunting medical diagnosis in 2010, one that initially suggested he might have a brain tumor, according to a new report.

The concern arose after Mr. Kennedy experienced significant memory loss and mental fogginess, prompting a close friend to worry about the severity of his condition. The situation led Mr. Kennedy to seek opinions from some of the nation’s leading neurologists, a number of whom had connections to his uncle, who passed away from brain cancer in 2009.

During a 2012 deposition that The New York Times has reviewed, Mr. Kennedy revealed that a few physicians identified a dark spot on his brain scans, leading them to the preliminary conclusion that he had a brain tumor.

Preparations were made for him to undergo surgery at Duke University Medical Center by the same surgeon who had treated his uncle. However, in an unexpected turn of events, Mr. Kennedy received a call from a physician at New York Presbyterian Hospital who offered a different diagnosis — a dead parasite was present in his brain, not a tumor.

The doctor said the abnormality seen on his scans “was caused by a worm that got into my brain and ate a portion of it and then died,” Mr. Kennedy said in the deposition. “I have cognitive problems, clearly,” he said in the 2012 deposition. “I have short-term memory loss, and I have longer-term memory loss that affects me.”

Mr. Kennedy shared with The Times that he has since recovered from the initial symptoms of memory loss and mental fogginess, reporting no lingering effects from the parasite, which, he noted, required no treatment.

When asked about any potential impact Mr. Kennedy’s past health issues might have on his fitness for presidential office, Stefanie Spear, a spokesperson for the Kennedy campaign, dismissed the concern.

“That is a hilarious suggestion, given the competition,” she said.