“She is lucky being Hillary Clinton and had a follow-up MRI — lucky that her team thought to do it,” said Dr. Brian D. Greenwald, medical director at JFK Johnson Rehabilitation Center for Head Injuries. “It could have potentially serious complications.”

The backup of blood flow could have caused a stroke or hemorrhage, according to Greenwald.

“Imagine this vein, where all the cerebral spinal fluid inside the head and spine no longer flows through this area,” he said. “You get a big back up and that itself could cause a stroke. In the long-term … the venous system can’t get the blood out of the brain. It’s like a Lincoln Tunnel back up.”