The most common symptom of sinus thrombosis is a headache. It usually builds over days, gets worse when lying down, coughing or straining, and does not behave like the person’s usual headaches. Other symptoms include blurred or double vision, seizures, weakness or numbness on one side, and confusion or drowsiness. Their clinical importance is that they can look like a migraine or a simple stroke, while the underlying clot needs specific imaging and anticoagulant treatment. Recognizing the pattern early is what prevents lasting brain injury.
What Sinus Thrombosis Is
Sinus thrombosis, more precisely cerebral venous sinus thrombosis (CVST), is a blood clot in the dural venous sinuses. These are the large channels that drain blood out of the brain. It has nothing to do with the air-filled nasal sinuses behind the face.
When a sinus is blocked, blood backs up inside the brain. Two things follow, and they explain almost every symptom:
- Raised intracranial pressure: cerebrospinal fluid is absorbed through the venous sinuses, so a blockage raises the pressure inside the skull. This causes headache, vision changes and vomiting.
- Local brain injury: congested veins leak, causing swelling, venous infarction and sometimes bleeding. This leads to seizures and focal deficits.
CVST is an uncommon cause of stroke. It affects younger adults more than typical arterial stroke does, and women more than men.
Sinus Thrombosis Symptoms and What They Signal
| Symptom | Typical features | Clinical implication |
|---|---|---|
| Headache | The most frequent symptom; often gradual and progressive, worse lying down or on straining. Occasionally sudden and severe (“thunderclap”). | Raised intracranial pressure; may be the only symptom |
| Visual blurring, transient vision loss, double vision | Swelling of the optic discs (papilledema); double vision from sixth nerve strain | Sustained high pressure can permanently damage vision |
| Nausea and vomiting | Often accompany the headache | Another sign of raised pressure |
| Seizures | Focal or generalized; more common than in arterial stroke | Irritation from venous congestion, infarction or bleeding |
| Weakness, numbness, speech difficulty | One-sided; may fluctuate or affect both sides | Venous infarction or hemorrhage in the brain tissue |
| Confusion, drowsiness, coma | Encephalopathy, especially with deep vein involvement | A severe pattern that needs urgent, often intensive, care |
| Eye swelling, bulging eye, eye movement palsy | Seen when the cavernous sinus is involved, often after facial infection | Septic thrombosis; needs antibiotics as well as other treatment |
Clinicians often group these into four overlapping syndromes: isolated raised intracranial pressure, focal neurological deficits, seizures, and encephalopathy. The syndrome depends on which sinus or vein is blocked, how quickly the clot formed and how well other veins compensate.
Why These Symptoms Are Easy to Miss
CVST is diagnosed late more often than most strokes. There are several reasons:
- The headache can look exactly like a migraine or tension headache.
- Symptoms can come on over days or even weeks rather than suddenly.
- A standard non-contrast CT scan is often normal early on.
- Patients are frequently young and otherwise healthy, so stroke is not suspected.
A clue I pay attention to in practice is a new or changed headache in someone with a clotting risk factor. Examples are a woman who is pregnant, recently postpartum or on estrogen-containing contraception, or someone with a known thrombophilia.
Risk Factors That Raise Suspicion
Like other clots, CVST usually arises from a combination of factors:
- Hormonal: combined oral contraceptives, pregnancy and the postpartum period, hormone therapy
- Inherited thrombophilia: factor V Leiden, prothrombin gene mutation, protein C, protein S or antithrombin deficiency
- Acquired conditions: antiphospholipid syndrome, cancer, inflammatory bowel disease, nephrotic syndrome, myeloproliferative neoplasms
- Local causes: ear, sinus or facial infections, meningitis, head injury, recent neurosurgery or lumbar puncture
- Other: dehydration, severe anemia, and certain medications
How Symptoms Lead to Diagnosis
When the symptoms fit, the key step is imaging of the venous system:
- MRI with MR venography (MRV): the preferred test. It shows the clot and any brain swelling, infarction or bleeding.
- CT venography (CTV): fast and widely available; a good alternative when MRI is not possible.
- Blood tests: blood count, clotting tests and inflammatory markers. A normal D-dimer makes CVST less likely but does not rule it out, especially with a long-standing headache.
- Eye examination: looks for papilledema.
- Thrombophilia testing: in selected patients once the acute phase is over, to guide how long to treat.
Treatment and Outlook
Anticoagulation is the cornerstone of treatment, and it is started even when the scan shows bleeding caused by the venous blockage. The aim is to stop the clot from growing and allow the vein to reopen.
- Acute phase: low molecular weight heparin or unfractionated heparin.
- Continuation: warfarin or, increasingly, a direct oral anticoagulant (DOAC), typically for 3 to 12 months. Treatment is longer when a persistent risk factor is present.
- Supportive care: seizure medication, treatment of raised pressure, fluids, and antibiotics for infection-related cases.
- Rescue therapies: endovascular clot removal or, rarely, surgery to relieve pressure for patients who worsen despite anticoagulation.
With prompt treatment, most patients recover well. Some have lingering headaches, fatigue or visual problems, so follow-up with neurology and hematology is worthwhile. Our blood clotting guide covers how clots form and how anticoagulants work.
When to See a Doctor
Seek emergency care straight away for:
- A new, severe or steadily worsening headache, especially with vomiting or blurred vision
- A sudden “worst ever” headache
- A seizure in someone with no history of epilepsy
- Weakness, numbness, speech difficulty or confusion
- Any of the above during pregnancy, after childbirth or while taking estrogen
Frequently Asked Questions
Is sinus thrombosis related to a sinus infection?
Usually not. The “sinuses” in sinus thrombosis are veins inside the skull. Infections of the ears, face or nasal sinuses can occasionally spread and cause a clot, particularly in the cavernous sinus.
How is a sinus thrombosis headache different from a migraine?
It is typically new or unlike previous headaches, tends to worsen over days, and is often worse lying down or on straining. It may come with vision changes, vomiting, seizures or weakness. Any headache with these features needs urgent assessment.
Can you have sinus thrombosis with only a headache?
Yes. Isolated headache from raised intracranial pressure is a recognized presentation, which is one reason the diagnosis is sometimes delayed. Imaging of the venous system settles the question.
Why give blood thinners if there is bleeding in the brain?
In CVST, the bleeding is caused by blocked veins backing up. Anticoagulation treats that cause by stopping the clot from growing and helping the veins reopen, so it is used even when a hemorrhage is present.
