U.S. Secretary of State Hillary Clinton was lucky that, being the top U.S. diplomat, her medical team had thought to do a follow-up MRI after her concussion last month, medical experts told ABC News on Tuesday.
The doctors said that Clinton's latest health update -- cerebral venous thrombosis -- is a rare and potentially "life-threatening" condition, but one from which the globe-trotting secretary of state is likely to recover from.
In an update from her doctors, Clinton's brain scans revealed a clot had formed in the right transverse venous sinus, and she was being successfully treated with anticoagulants.
"She is lucky being Hillary Clinton and had a follow-up MRI -- lucky that her team thought to do it," Dr. Brian D. Greenwald, medical director at JFK Johnson Rehabilitation Center for Head Injuries, told ABC News. "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."
A transverse sinus thrombosis is a clot arising in one of the major veins that drains the brain. It is an uncommon but serious disorder.
According to Greenwald, the clot was most likely caused by dehydration brought on by the flu, perhaps exacerbated by the concussion she recently suffered.
"The only time I have seen it happen is when people are severely dehydrated and it causes the blood to be so thick that it causes a clot in the area," Greenwald told ABC News. "It's one of the long-term effects of a viral illness."
Drs. Lisa Bardack of the Mt. Kisco Medical Group and Dr. Gigi El-Bayoumi of George Washington University discovered the clot during a routine follow-up MRI on Sunday.
"This is a clot in the vein that is situated in the space between the brain and the skull behind the right ear," they said in a statement released Tuesday. "It did not result in a stroke, or neurological damage. To help dissolve this clot, her medical team began treating the secretary with blood thinners. She will be released once the medication dose has been established."
Clinton is "making excellent progress," according to her doctors. "She is in good spirits, engaging with her doctors, her family, and her staff."
Clinton, 65, was hospitalized at New York-Presbyterian Hospital Sunday. She suffered a concussion last month after she hit her head when she fainted because of dehydration from a stomach virus, according to an aide.
Clinton's lengthy absence from public life had sparked claims from some of her fiercest critics that she was faking illness to avoid testifying before lawmakers investigating a deadly attack on a U.S. mission in Libya.
The September 11 assault on the U.S. mission in eastern Benghazi, in which the U.S. ambassador and three other American officials were killed, sparked a political firestorm in the United States. A subsequent State Department inquiry found that security at the mission was "grossly inadequate."
A Senate report released Monday confirmed that the decision to keep the U.S. embassy in Benghazi open despite increasingly dangerous threats and the knowledge that the mission's security detail would be inadequate to deal with the threats was a "grievous mistake," resulting in the deaths of the four Americans.