What Is Cerebral Venous Thrombosis?

Clots in the Veins of the Brain

Human Brain
Human Brain. Matt Cardy / Stringer / Getty Images

Let me give you a scenario.  A 35-year-old woman had a severe headache shortly after giving birth to her first child.  She then lost consciousness with rhythmic jerking suggestive of a seizure.  When she stopped seizing, she remained confused for a longer period than doctors normally expected following a seizure.  A CT scan of the head was ordered, which was interpreted as being suggestive of a superior venous sinus thrombosis.


What is Cerebral Venous Thrombosis?

Most people associated blood clots in the brain with ischemic stroke, which is due to a blocking of an artery.  However, clots can also form in the cerebral veins.  Cerebral venous thrombosis (CVT) is believed to be less common than arterial stroke, but can also be more difficult to recognize. 

What Are the Signs and Symptoms of CVT?

Because the veins drain fluid from the intracranial space, fluid builds up if the veins are blocked.  This can result in elevated  intracranial pressure, which leads to headache, nausea, and sometimes blurred vision.  A headache is usually in just one part of the head, and gradually worsens over several days, though exceptions do occur.  A headache may be worse when laying flat.  Depending on the location of the vein, you may have focal deficits, such as weakness or numbness on one side of the body.  Seizures are also common in CVT.

In severe cases, you can get changes in mental status that may progress to coma

What Causes CVT?

There are several risk factors for a blood clot forming in any vein, including the cerebral veins.  These include any predisposition towards forming clots, including pregnancy, oral contraceptives, cancer, infection or genetic conditions.

  Some such risk factor is present in the majority of CVT cases.

When the blood clot forms, fluid can no longer appropriately drain out of that region of the brain. As a result, fluid backs up and plasma may leak from the veins into the brain.  As pressure continues to build, venous hemorrhage or capillary rupture may also result. 

How Common is CVT?

While the estimated prevalence of CVT varies somewhat between studies, most agree that it is probably uncommon, occurring in less than 1.5 per 100,000 people yearly.  The average age of onset is 34 years old in women and 42 years in men.  The disorder is about three times more common in women than men, which may be due to known risk factors for clotting such as oral contraceptives and pregnancy.   Some studies suggest that CVT may be more common in children than adults.

How is CVT Diagnosed? 

A magnetic resonance image (MRI) of the brain in combination with MR venography is probably the best method of diagnosing CVT.  Moreover, the MRI can give doctors a sense of how old the clot is, as the appearance on MRI changes over time.  The technique isn’t perfect, though, as there is a lot of natural variation in vein structures between individuals.

  What may appear to be a clot may, in fact, be what is called a hypoplastic sinus, just a normal variation in which one part of the vein is small or even absent. Additional MRI techniques may be useful in distinguishing these variants from something more concerning.

Head CT may be the first test performed in a hospital for someone with CVT, largely to exclude other disorders.  That said, the CT is normal in up to 30 percent of people with CVT.  When an abnormality is found, it is often nonspecific, meaning that the abnormality could be due to a CVT or to something else.  A CT venogram, in which a contrasts is injected so that radiologists can better visualize the vein, can be both fast and useful, but the deep veins are not well seen, and the technique exposes patients to the risks of contrast injection and radiation.


How is CVT Treated? 

The mainstay of treatment for CVT is anticoagulation to thin the blood. Most of the time this involves a use of heparin.  In some cases, an intravenous catheter may be used to remove the clot during an endovascular procedure, though there have been no well-controlled trials to study this technique. Symptoms such as seizures or elevated intracranial pressure must also be managed, which sometimes may require a stay in an intensive care unit (ICU).

What is the Prognosis?

Less than 5 percent of patients with recognized CVT die within the first 30 days as a result of their disorder.  The risks are highest if the thrombosis is deep in the brain, or associated with severe altered mental status.

In the longer run, about 15 percent of patients suffer from death or a serious decline in the quality of their life over 16 months after a CVT.  Men tend to do worse than women.  Other risks of poor outcome include a CNS infection, cancer, hemorrhage, coma, or age over 37 years.  The risk of recurrent CVT is relatively low at 2 to 4 percent. 


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