Dec. 31, 2012 -- Hillary Clinton's latest health update -- cerebral venous thrombosis -- is a rare and potentially "life-threatening" condition, according to medical experts, 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," 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."
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 a 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," said Greenwald. "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 today. "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 earlier this month after she hit her head when she fainted because of dehydration from a stomach virus, according to an aide.
Dehydration can also precipitate fainting, according to Dr. Neil Martin, head of neurovascular surgery at University of California, Los Angeles Medical Center.
He agreed that the condition could potentially have caused a brain hemorrhage or stroke and been fatal.
"In patients with no symptoms after many days, full recovery is the norm," said Martin. "However, some cases show extension of the thrombus or clot into other regions of the cerebral venous sinuses, and this can worsen the situation considerably -- thus the use of anticoagulants to prevent extension of the thrombus."
But, he said, anticoagulants can be a "double-edged sword." With even a tiny injury within the brain from the concussion, these medications can cause "symptomatic bleed," such as a subdural or intracerebral hemorrhage.
The clot location is not related to the nasal sinuses, but are rather large venous structures in the dura or protective membrane covering the brain, which drains blood from the brain.
Hillary Clinton's Clot Could Have Been Dangerous
There are both right and left transverse venous sinuses. "If one is blocked by thrombosis, the other one can take over as a detour," he said. "Thrombosis of the other nonduplicated sinuses -- the superior saggital or straight sinuses - is usually much more dangerous."
Dr. Keith Black, head of neurosurgery Cedars Sinai Medical Center in Los Angeles, said he was "surprised" by Clinton's diagnosis. "If I were her treating physician, you would have to ask, why did she develop a thrombosis. A very unusual event following a concussion without a skull fracture."
He speculated that Clinton may have had a "predisposition to clot formation." She had a deep vein thrombosis, a clot in the leg, in 1998.
"It is likely she will be evaluated for a clotting abnormality," he said.
Treatment of this condition consists of reversing the cause when known, controlling seizures if present, controlling the blood pressure in the head, and anticoagulation. Anticoagulation is the most essential.
The doctors all agreed her prognosis was good, providing the clot does not expand, a likelihood of about 1 percent, according to Black. Over time the clot will either reabsorb or scar down.
A worst case scenarios would be that the vein would occlude and she could get a venous infarct or stroke in the temporal lobe, the area responsible for speech.
But Greenwald is convinced Clinton's excellent health care team "caught it early."
"Assuming it was a follow-up MRI, that probably would not have happened for regular people," he said. "I suspect a lot of other people have poorer outcomes. I would call her lucky."
Clinton and her doctors say that with regular monitoring, she will have a "full recovery."
"Knowing Hillary Clinton, she can do plenty of stuff from home and at her bedside," said Greenwald. "It's not a situation where you want to throw her on a long plane ride to the Middle East, though. She will need to be followed closely medically. But she'll be back to herself in no time."