CVT stands for cerebral venous thrombosis, a type of stroke caused by a blood clot in the veins that drain blood from the brain. It affects roughly 8 to 12 people per million each year, making it uncommon but serious. Unlike the more familiar type of stroke caused by a blocked artery, CVT blocks the outflow of blood, causing pressure to build inside the skull.
How CVT Affects the Brain
The brain’s veins and large drainage channels (called dural sinuses) carry used blood back toward the heart. When a clot forms in one of these veins or sinuses, blood backs up behind it. As pressure in the surrounding small vessels rises, several things can happen in a cascade: the brain tissue doesn’t get enough fresh blood flow, fluid leaks through damaged vessel walls into the brain (edema), and fragile veins can rupture, causing bleeding into the brain itself.
There’s a second mechanism that compounds the damage. The brain produces cerebrospinal fluid continuously, and that fluid is normally reabsorbed into the large sinuses at the top of the skull. When a clot blocks a sinus, the fluid can’t drain properly. Pressure inside the skull climbs, which further strains the already congested veins and worsens swelling and bleeding. This dual mechanism, venous congestion plus rising fluid pressure, is what makes CVT dangerous even though the clot itself may be relatively small.
Who Is Most at Risk
CVT is more common in women, who make up about 55% of cases. The gap is driven almost entirely by women of reproductive age. After menopause, men and women develop CVT at similar rates.
Hormonal contraceptives are the single most studied risk factor. Women aged 15 to 50 who use oral contraceptive pills have roughly 7.5 times the odds of developing CVT compared to women who don’t, with some studies placing the increase as high as 22-fold. Carrying an inherited clotting disorder such as Factor V Leiden pushes the risk even higher, especially when combined with hormonal contraceptives.
Other recognized risk factors include:
- Pregnancy and the postpartum period, when the blood naturally becomes more prone to clotting
- Infections, particularly of the sinuses, ears, or brain membranes
- Cancer and inflammatory conditions that alter blood clotting
- Dehydration, recent surgery, or prolonged immobility
- Inherited clotting disorders (thrombophilias)
In a meaningful number of cases, no clear cause is ever identified.
Symptoms to Recognize
Headache is the hallmark symptom, present in the vast majority of cases. It often builds over days rather than striking suddenly, which can make it easy to dismiss. The headache typically worsens with lying down or straining, reflecting the rising pressure inside the skull. Unlike a typical tension headache, it may not respond to over-the-counter painkillers and tends to intensify progressively.
Beyond headache, symptoms depend on where the clot sits and how much pressure has built up. Seizures are common and sometimes the first obvious sign. Vision changes, particularly blurred or double vision, can occur when swelling compresses the nerves behind the eyes. Weakness or numbness on one side of the body, difficulty speaking, and confusion are possible when brain tissue is directly affected by swelling or bleeding. In severe cases, consciousness can decline rapidly.
Because symptoms overlap with migraines, meningitis, and other conditions, CVT is frequently misdiagnosed on the first visit. A high index of suspicion matters, especially in younger women with new, unusual headaches and any additional neurological symptoms.
How CVT Is Diagnosed
A standard CT scan of the head can sometimes show clues, like bleeding or swelling, but it often looks normal in early CVT. The diagnosis requires specialized imaging that visualizes the veins themselves. Two main options exist: CT venography (a CT scan with contrast dye timed to highlight veins) and MR venography (an MRI technique that maps blood flow through the venous system).
CT venography has a sensitivity of about 95% and specificity of 91% compared to the gold standard of catheter angiography. It’s fast and widely available, which makes it a practical first choice in emergency settings. MR venography works well too and avoids radiation, but it carries a higher risk of false positives, particularly when a person has a naturally smaller vein on one side of the head, a common anatomical variant.
MRI with specific sequences is the most sensitive tool for seeing the clot material itself. In unclear cases, catheter angiography, where dye is injected directly into the blood vessels through a thin tube, remains the definitive test but is reserved for situations where other imaging is inconclusive.
Treatment
The core treatment for CVT is blood thinners (anticoagulation), even when there is bleeding in the brain. That sounds counterintuitive, but the bleeding in CVT is caused by venous congestion, and the only way to resolve it is to treat the clot. Guidelines from the American Heart Association recommend starting with injectable blood thinners, typically a type called low-molecular-weight heparin, because it has more predictable effects and a better safety profile than older intravenous alternatives.
After the initial phase, treatment transitions to an oral blood thinner. The traditional choice has been warfarin, though newer oral anticoagulants are increasingly used. How long you stay on blood thinners depends on the underlying cause. If the trigger was temporary, like dehydration or oral contraceptives that have since been stopped, treatment typically lasts 3 to 12 months. If you have a permanent clotting disorder or a history of recurrent blood clots, lifelong anticoagulation may be recommended.
For women who develop CVT during pregnancy, injectable blood thinners are continued throughout pregnancy and for at least 6 weeks after delivery, for a minimum total of 3 months. Warfarin and newer oral blood thinners are not safe during pregnancy.
Long-Term Outlook
The prognosis for CVT is better than for most other types of stroke. At least 80% of survivors recover with a favorable neurological outcome, and only 7% to 20% are left with lasting disability. The risk of the clot coming back in the same location is low, roughly 3% based on long-term follow-up studies. However, about 7% of people go on to develop a blood clot elsewhere in the body, such as a deep vein thrombosis in the leg or a pulmonary embolism, translating to an overall recurrence rate of about 2 per 100 people per year for any type of venous clot.
Recovery time varies widely. Some people bounce back within weeks, while others deal with lingering headaches, fatigue, or cognitive difficulties for months. Seizures that developed during the acute phase sometimes require ongoing medication, though many people are eventually able to taper off.
CVT in Newborns and Children
CVT also occurs in infants, though it looks quite different. In newborns, the triggers are typically dehydration, infection (sepsis or meningitis), low oxygen at birth, or recent surgery. The symptoms are nonspecific: irritability, seizures, or a generally unwell appearance, which makes the diagnosis easy to miss or delay. Premature infants with CVT are more than twice as likely to have no obvious symptoms at all compared to full-term infants.
The location of the clot and the pattern of brain injury differ by gestational age. Preterm infants tend to develop clots in the side drainage channels and show white matter injury, while full-term infants more commonly have clots in the central sinuses with bleeding in deeper brain structures.