PITTSBURGH (KDKA) — Cerebral venous thrombosis is a condition that affects five in a million adults each year.

Hillary Clinton is one of them. But she’s not the most typical patient.

Dr. James Wilberger, a neurosurgeon at Allegheny General Hospital, says, “it’s typically young women,” young women on hormonal birth control, or who are pregnant, or who have just delivered.

Not being able to keep anything down because of a viral illness can lead to the problem.

“It’s more common in situations where people become very dehydrated,” he explains.

Trauma, for example a concussion, can be a minor factor.

“I’ve never seen someone with a concussion develop a sinus thrombosis,” Dr. Wilberger continues. “If you have a fracture of the skull, especially if the fracture is indented, it can push against those veins or one the veins and cause it to clot off.”

And clotting disorders are found in two-thirds of people with this.

“Some people have a genetic predisposition to developing blood clots,” he says.

Usually, the first symptom is a headache, though it can be much worse.

“Some people can present in coma though, especially if it involves a lot of the veins,” Dr. Wilberger adds.

The diagnosis is clinched with a test called an MRV — or magnetic resonance venogram.

“It’s like an MRI but of the veins inside the skull,” he continues. “And that diagnoses it 100 percent of the time, with high accuracy.”

Clinton’s clot is in a space just behind the right ear — a space called the right transverse sinus. Not a sinus like you’d think of with your nose, but a space that carries blood from the brain back to the heart.

Treatment is with anticoagulants. But doctors need to be careful because known complications include stroke, brain swelling and bleeding.

In general, the prognosis is good with nearly 90 percent having either a full recovery or just slight impairment.

“The folks who don’t do well with this have multiple veins clotted off,” Dr. Wilberger adds.

In Clinton’s case — only one vein is involved.

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