Like every organ of our body, the brain has a system of draining veins by which oxygen-depleted blood is channeled back to the lungs, where it can once again be repleted with oxygen. This system of draining veins begins as a collection of small channels that receive blood from a myriad of small areas from all over the brain. As these tiny veins extend away from the brain's tissues, they become fused with one another to form larger and larger veins that finally gather between the brain and the skull bone to form what is called the "dural sinuses." Therefore, the dural sinuses are the largest canals through which blood flows out of the brain, on its way back to the lungs. There are just a handful of dural sinuses, and they are called:
- Superior and inferior sagital sinus
- Superior and inferior petrosal sinus
- Transverse sinus
- Sigmoid sinus
- Straight sinus
- Cavernous sinus
- Confluence of sinuses
What is dural sinus thrombosis?Simply put, thrombosis is a word that describes the formation of a blood clot. Therefore, dural sinus thrombosis is the formation of a blood clot inside of one of the dural sinuses described above.
How can dural sinus thrombosis cause a stroke?When a blood clots sits inside of one of the brain's sinuses, it causes a back up of blood inside the venous system of the brain, preventing blood from leaving the brain's tissues. At first, this is not a problem, as the small veins have some room to enlarge in order to accommodate for the extra blood. But as time goes on and new oxygen-rich blood continues to enter the brain's tissues through the arteries, the extra blood begins to cause pressure on the walls of these arteries until they burst, and cause bleeding inside the brain. This event causes a hemorrhagic stroke.
What are the symptoms of dural sinus thrombosis?One of the known features of dural sinus thrombosis is that it can cause a multiplicity of symptoms which can range from a mere headache to a sudden and complete paralysis of one side of the body. However, it is known that more than 90% of people with dural sinus thrombosis complain of severe headaches, while 50% of them have typical stroke symptoms. Yet approximately 40% of them have seizures. In some isolated cases, depending on the specific dural sinus that is affected, people can also have memory loss or they can stop speaking unexpectedly.
When a person's symptoms consist of only headaches and blurry vision, dural sinus thrombosis is commonly confused with a condition known as benign intracranial hypertesion, also known as pseudotumor cerebri.
How is dural sinus thrombosis diagnosed?Once in the emergency room doctors first perform a full neurological exam, and a CT scan of the brain. The CT scan helps doctors find out if there is bleeding inside the brain. If this is the case preparations are made for a possible surgery to drain the blood. However, in order to diagnose a dural sinus thrombosis doctors must perform a test known as magnetic resonance venography or MRV, a test which is similar to a conventional MRI, but which only shows blood inside the veins of the brain, and the skull. The test typically shows an empty area where the blood clot is located.
When MRV is not available, regular CT angiography can also be used to visualize the dural sinuses.
How is dural sinus thrombosis treated?
- Surgical treatments:
When dural sinus thombosis causes a large amount of bleeding inside the brain, surgery is required in order to drain the blood out of the skull. This is important as bleeding in the brain can lead to rapid herniation, and death. The procedure performed is called a decompressive hemicraniectomy. In some cases, increased intracranial pressure from large strokes requires the induction of hypothermia, or cooling of the body's temperature, which helps to prevent further damage to the brain. Some experimental treatments are also available in selected hospitals across the country, in which blood clots can be broken up inside the affected sinus using special endovascular thrombolysis techniques.
- Medical treatments:
Unless it is medically contraindicated, every person who is diagnosed with dural sinus thrombosis should receive long term treatment with blood thinners, such as heparin, coumadin, and lovenox. These medications are given in order to prevent the enlargement of the blood clot that sits inside the affected dural sinus, and to prevent the formation of new blood clots which could lead to new and possibly worse strokes.
Who is at risk of dural sinus thrombosis?Eighty-five percent of people who are diagnosed with dural sinus thrombosis have a propensity to form blood clots. Some of the conditions or events that make people more likely to form blood clots include:
- Head injury
- The last three months of pregnancy
- Delivering a baby
- The use of birth control pills
- Lumbar punctures (spinal taps)
- Infections, especially in the face, eyes or ears
Stam, Jan; Thrombosis of the cerebral veins and sinuses; New England Journal of Medicine(2005) 352:17:1791-8
Bradley G Walter, Daroff B Robert, Fenichel M Gerald, Jancovic, Joseph Neurology in clinical practice, principles of diagnosis and management. Fourth Edition, Philadelphia Elsevier, 2004.