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I'm a neurologist who would like to explain a bit about the kind of blood clot Sec. of State Clinton suffered. The technical term for it is a cerebral venous sinus thrombosis. The brain's venous system ultimately drains to a series of large venous sinuses, which are formed by the layers of tissue that wrap the outside of the brain and wrap the inside of the skull. Follow after the jump for more information, including some illustrations of this venous system.

Everyone is probably familiar with where the venous sinuses ultimately drain: the two jugular veins on either side of your neck. But before getting there, the blood goes through several other twists and turns first. Here are two illustrations, courtesy of Gray's Anatomy:

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I'm not claiming to have any knowledge or access to Mrs. Clinton's medical records, so I won't speculate on how severe her clot is. What I can say is that, based on the CNN article's description of a blood clot behind her right ear it is likely in either the transverse or sigmoid sinus. The good news is, as the pictures show, there are two ways for the blood to drain. More good news is the CNN article says she is doing quite well.

But what are possible problems from this kind of blood clot? The main issue is that the venous blood flow slows down and possibly stops. This could lead to tissue swelling as fluid that's normally carried away from the brain stays put. It can also lead to problems because the brain needs a lot of oxygen and the venous blood has already stopped carrying it. Lastly, it can lead to cellular damage and breakdown of brain tissue as the toxins and waste products generated by normal brain function aren't carried away.

In severe cases, it can lead to increases in pressure inside the brain: think of the brain as a sponge inside a concrete box, with two hoses spraying water in and draining water out. Normally the system works to keep the water flowing in and out at equal rates, and to keep the sponge smaller than the box. If one of those hoses becomes completely blocked, the water can build up in the sponge and there's nowhere for the sponge to go once it hits the boundaries of the concrete box... This can lead to very bad headaches, vision loss, changes in thinking, seizures, bleeding in the brain tissue as cells break down, etc. The good news is there are medical and surgical treatments that work well for just about all of these complications. Bleeding in the brain is the only one that can sometimes be very difficult to treat.

The typical case is someone who has new headaches, perhaps a little vision change, along with the possibility of a strange pulsing sound in their ears. A special kind of MRI scan, called a MRV, can look for blood clots in these sinuses. A normal brain MRI, usually done at the same time, looks for problems with swelling, bleeding, etc. Once a cerebral venous sinus thrombosis is seen, the normal treatment is anticoagulation. Usually it's a combination of IV and oral pills, as the pills take a few days to start working, and then long-term treatment with pills. The CNN article notes that Mrs. Clinton has been started on such treatment. Over time, the blood clot can break down and be resorbed. In some cases, part of the blood clot may be permanent but a new passage for blood is formed inside it. This is called complete or partial recanalization.

Long-term, most people with this problem do quite well. Based on 2006 review of 19 studies following 1488 patients around the world for 6 months or more on average, 88% of people with a cerebral venous thrombus had full recovery or only minor complications (occasional headache, minor trouble with concentration or memory, etc.). Only 2.8% had recurrence over the course of the study. There are factors like other medical or genetic conditions that predispose one to blood clots that could change the outcome.

Hopefully, now it is clear exactly what Mrs. Clinton suffered from. And I hope you'll all join me in wishing Secretary of State Clinton all the best and a speedy recovery!

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