Sinus thrombosis, properly called cerebral venous sinus thrombosis (CVST), is a blood clot in one of the large veins that drain blood from the brain. It is caused by a mix of clot-promoting factors such as pregnancy, hormonal contraception, inherited clotting disorders, infection and dehydration. It is diagnosed with MRI or CT venography, and it is treated first with anticoagulants (blood thinners), with clot-removal procedures reserved for patients who worsen despite treatment. Caught early, most people recover well.
Because the condition is rare and its main symptom, headache, is so common, it is easy to miss. This article covers why it happens, how it presents, how it is confirmed, and where treatment is heading. For a companion overview, see our article on venous sinus thrombosis causes, diagnosis and treatment.
What Is Sinus Thrombosis?
The brain’s blood drains through a network of channels called the dural venous sinuses, which sit between layers of the tough membrane surrounding the brain. The largest include the superior sagittal sinus along the top of the head and the transverse and sigmoid sinuses toward the back. From there, blood flows into the jugular veins and back to the heart.
When a clot blocks one of these sinuses, blood backs up. Pressure inside the skull rises, fluid leaks into brain tissue, and in some cases a venous infarct (an area of damaged brain) or bleeding develops. This is different from the more familiar arterial stroke, in which a clot blocks blood flowing into the brain.
CVST can occur at any age, including in newborns and children, but it most often affects young and middle-aged adults and is more common in women.
Causes and Risk Factors
Clots form when three conditions combine: sluggish blood flow, damage to the vessel wall, and blood that clots too readily, known as hypercoagulability. In CVST, more than one risk factor is often present.
| Risk factor group | Examples | Why it raises risk |
|---|---|---|
| Hormonal | Pregnancy, the weeks after childbirth, estrogen-containing contraceptives, hormone therapy | Estrogen increases clotting factor levels |
| Inherited thrombophilia | Factor V Leiden, prothrombin gene mutation, protein C, protein S or antithrombin deficiency | Blood clots more easily or natural anticoagulants are reduced |
| Acquired clotting disorders | Antiphospholipid syndrome, cancer, nephrotic syndrome, inflammatory bowel disease | Systemic tendency toward clotting |
| Local causes | Ear, sinus or face infections, head injury, neurosurgery | Inflammation or damage near the venous sinuses |
| Blood disorders | Polycythemia vera, essential thrombocythemia, severe iron deficiency anemia | Thicker blood or abnormal platelet behavior |
| Other | Dehydration (especially in children), obesity, certain medicines | Slower flow and a prothrombotic state |
A rare but well-described cause is vaccine-induced immune thrombotic thrombocytopenia (VITT), seen after adenoviral-vector COVID-19 vaccines. In VITT, antibodies activate platelets, causing clots together with a low platelet count, which changes how the condition must be treated.
How Platelets and Clotting Proteins Drive the Clot
A venous clot is built mainly from fibrin and trapped red cells, but platelets play an active part. Platelet activation exposes surfaces on which clotting factors assemble, speeding thrombin generation and fibrin formation. Once a clot starts in a sinus, slow flow behind it encourages further growth.
This is why anticoagulants, which slow thrombin generation, are the backbone of treatment. They stop the clot from extending and give the body’s own fibrinolytic system time to dissolve it.
Signs and Symptoms
Symptoms can develop suddenly or over days to weeks, which is part of why diagnosis is often delayed. Common features include:
- Headache: the most frequent symptom, often worsening over days, worse when lying down or straining, and sometimes sudden and severe.
- Seizures: focal or generalized, more common than in arterial stroke.
- Focal neurological deficits: weakness on one side, speech difficulty, or visual loss.
- Signs of raised pressure: blurred or double vision, nausea and vomiting, and papilledema (swelling of the optic nerve head seen on eye examination).
- Drowsiness or confusion, particularly when deep veins are involved.
Diagnosis and Testing
The key is suspecting the condition. A plain CT scan of the head is often the first test, but it can look normal. The diagnosis is confirmed by imaging the veins directly:
- MRI with MR venography (MRV): the preferred test, showing both the clot and any brain changes.
- CT venography: fast, widely available and accurate when MRI is not possible.
- Catheter angiography: rarely needed, mainly when noninvasive imaging is unclear or an intervention is planned.
Blood tests support the workup. A normal D-dimer makes CVST less likely but does not exclude it, particularly when symptoms have lasted a while. A full blood count checks platelets and looks for blood disorders, and thrombophilia testing is considered in selected patients, often after the acute phase because some results are affected by the clot or by treatment.
Treatment and Emerging Options
Anticoagulation first
Treatment usually begins with low molecular weight heparin or unfractionated heparin, even when there is some bleeding in the brain, because the bleeding is caused by the venous blockage and stopping the clot’s growth is the priority. After stabilization, patients move to an oral anticoagulant. Warfarin has long been standard, and direct oral anticoagulants such as dabigatran are now increasingly used as an alternative in suitable patients. Pregnancy and antiphospholipid syndrome are important exceptions where the choice of drug differs.
Typical treatment lasts roughly 3 to 12 months, depending on whether the trigger was temporary. People with recurrent clots or a severe thrombophilia may need longer, sometimes indefinite, therapy.
When more is needed
- Endovascular therapy: mechanical clot removal or direct delivery of clot-dissolving drugs, considered for patients who deteriorate despite anticoagulation. Its exact place is still being defined.
- Decompressive surgery: for large swelling or bleeding that threatens brain herniation.
- Supportive care: seizure medicines, treatment of raised pressure, and treating the underlying infection or cause.
VITT is managed differently: heparin is avoided, and treatment includes non-heparin anticoagulants and intravenous immunoglobulin.
When to See a Doctor
Seek emergency care for a sudden severe headache, a headache with seizures, weakness, confusion or vision changes, or a new, steadily worsening headache in pregnancy, after childbirth, or while taking estrogen. Tell the team about any recent vaccination, infection or clotting history. For more on clots elsewhere in the body, visit our blood clotting guide.
Frequently Asked Questions
Is sinus thrombosis a type of stroke?
Yes, it is classed as an uncommon form of stroke, but it affects the veins draining the brain rather than the arteries supplying it. It tends to affect younger people and often has a better outlook than arterial stroke when treated promptly.
Can I take the contraceptive pill again after CVST?
Estrogen-containing contraception is generally avoided after CVST. Progestogen-only or non-hormonal methods are usually preferred, and the choice should be made with your doctor.
Can sinus thrombosis come back?
Recurrence is uncommon but possible, and it is more likely when a persistent risk factor remains. Your hematologist will weigh this when deciding how long anticoagulation should continue.
Will I recover fully?
Many people recover completely or with minor symptoms. Some have lingering headaches, fatigue or concentration problems, which often improve over months with follow-up and rehabilitation.
