Sinus thrombosis, formally called cerebral venous sinus thrombosis (CVST), is a blood clot that forms in the large drainage channels of the brain. These channels, called dural sinuses, carry used blood out of the brain and back toward the heart. When a clot blocks one of them, blood backs up, pressure rises inside the skull, and the brain can swell or even bleed. It affects roughly 14 to 20 people per million each year and is three times more common in women than men.
How Blood Drains From the Brain
Your brain’s veins empty into a network of large, rigid channels sandwiched between two layers of the brain’s outer lining. These dural sinuses funnel blood toward the jugular veins in the neck and ultimately back to the heart. The same sinuses also absorb cerebrospinal fluid, the clear liquid that cushions the brain and spinal cord. Cerebrospinal fluid passes through tiny structures called arachnoid granulations that poke into the sinuses, where it gets reabsorbed into the bloodstream.
When a clot blocks a sinus, two things go wrong at once. First, blood can’t leave the brain efficiently, so pressure builds in the smaller veins and capillaries upstream. That rising pressure starves brain tissue of fresh blood flow, causes swelling, and can rupture small vessels. Second, cerebrospinal fluid can no longer drain properly, so it accumulates and pushes intracranial pressure even higher. This double hit is what makes sinus thrombosis dangerous.
Which Sinuses Are Most Often Affected
The superior sagittal sinus, which runs along the top of the brain from front to back, is the most frequently clotted. Its length and relatively narrow diameter make it vulnerable. The transverse sinuses, which wrap around the back of the skull, are the second most common site. The left transverse sinus is often naturally smaller than the right, giving it slower blood flow and a higher clotting risk. Clots can also extend from one sinus into another or involve the deeper internal veins, which tends to cause more severe symptoms.
Symptoms and Warning Signs
Headache is by far the most common symptom, present in more than 85% of cases. Unlike a typical tension headache, it often worsens over days rather than hours, may be worst when lying down, and frequently resists over-the-counter painkillers. Some people describe it as the worst headache of their life, while others notice a slowly building pressure that doesn’t let up.
Beyond headache, symptoms depend on where the clot sits and how much pressure it creates. Possible signs include:
- Vision changes: blurred or double vision, sometimes with swelling of the optic nerve (found in about 60% of patients in one study)
- Seizures: more common in sinus thrombosis than in typical stroke
- Weakness or numbness: usually on one side of the body, similar to an arterial stroke
- Confusion or difficulty speaking
- Loss of consciousness in severe cases
Symptoms can develop over hours or creep in over weeks, which is one reason CVST is often misdiagnosed initially. A young woman with a persistent, worsening headache and no clear cause is a classic presentation that should raise suspicion.
Who Is at Risk
Anything that makes blood more likely to clot, slows venous flow, or damages the vessel wall can contribute. The most common risk factors include:
- Hormonal factors: oral contraceptives, pregnancy, and the weeks after delivery are the biggest contributors to the female predominance of this condition
- Inherited clotting disorders: genetic conditions that make blood clot too easily
- Infections: ear infections, sinus infections, and meningitis can spread inflammation to nearby venous sinuses
- Dehydration: especially significant in children and newborns
- Head or neck trauma and recent surgery
- Cancer and chronic inflammatory diseases
In children, the triggers look somewhat different. Serious infections, dehydration, head and neck trauma, central venous catheters, mechanical ventilation, and chronic inflammatory disease are all associated with pediatric cases. Newborns are particularly vulnerable during birth complications or severe dehydration.
How It Is Diagnosed
Standard brain imaging like a plain CT scan can miss sinus thrombosis entirely, especially early on. The key is adding a venography component, which specifically maps the venous sinuses. CT venography (a CT scan with contrast dye timed to fill the veins) has a sensitivity of about 95 to 96% and specificity near 99%, making it an excellent first-line test in emergency settings where speed matters.
MRI combined with MR venography is considered the gold standard because it shows both the clot and any brain tissue damage without radiation. It’s particularly useful for follow-up imaging to track whether the clot is dissolving. If you arrive at an emergency department with a suspicious headache, you’ll likely get a CT venogram first simply because it’s faster, with an MRI to follow if needed.
Complications
Brain bleeding occurs in roughly one-third of CVST patients. This can range from small areas of oozing within swollen brain tissue to larger, more dangerous bleeds. The bleeding happens because backed-up venous pressure ruptures small blood vessels, which is a different mechanism than the bleeding seen in a typical hemorrhagic stroke.
Persistently elevated intracranial pressure can also damage vision over time by compressing the optic nerves. In rare, severe cases, massive swelling can become life-threatening and require emergency intervention to relieve pressure.
Treatment and Recovery
The core treatment is blood-thinning medication (anticoagulation). This may seem counterintuitive when bleeding is already present in the brain, but thinning the blood prevents the clot from growing and allows the body’s natural clot-dissolving systems to work. Treatment typically starts with injectable blood thinners in the hospital, then transitions to oral blood thinners for several months afterward. The exact duration depends on whether an underlying cause was found and how reversible it is.
If the cause was temporary, like oral contraceptives or a recent infection, anticoagulation may last 3 to 6 months. If a permanent clotting disorder is identified, longer or even lifelong treatment may be necessary. During this time, you’ll have regular blood work and follow-up imaging to confirm the clot is resolving.
For patients with dangerously high intracranial pressure, additional measures to reduce that pressure may be needed, including medications to decrease cerebrospinal fluid production or, in extreme cases, surgical procedures to relieve swelling.
Long-Term Outlook
The prognosis is substantially better than most people expect from a condition involving brain clots. In a large multicenter study, about 89% of patients achieved complete recovery, and an additional 4% recovered enough to live independently. Most improvement happens in the first few months, though some symptoms like headache and fatigue can linger longer.
The most common lasting issue is headache, which can persist for months after the clot itself has resolved. A small percentage of patients develop ongoing elevated intracranial pressure that requires continued management. Seizures that occur during the acute phase don’t always mean you’ll need long-term anti-seizure medication; the decision depends on how many occurred and whether brain tissue was permanently damaged. Recurrence is relatively uncommon, occurring in roughly 2 to 4% of cases per year, with higher rates in people who have an underlying clotting disorder that wasn’t addressed.