What is Venous Sinus Thrombosis?
Venous sinus thromboses (VST) are when blood clots form in the primary veins inside the brain. These blood clots can either happen for a specific reason or without a known cause. The symptoms you may experience vary depending on where the clot is located and how big it is. These clots commonly develop in areas such as the dural sinuses (a network of veins in the brain), the cavernous sinus, and deep veins within the cortex layer of the brain.
What Causes Venous Sinus Thrombosis?
A venous sinus thrombosis is a blood clot that forms in the brain’s veins. This can occur for the same reasons as blood clots in other veins. Anything that can make blood clots more likely to form can contribute to the development of this condition.
For instance, you may be at a higher risk if your blood is thicker than normal, a condition known as increased coagulability, or if your blood flow is slower in certain parts of your veins. You also could be more at risk of getting a venous sinus thrombosis if you have inherited a disorder that makes your blood clot more easily, have a type of cancer that increases clotting, are using birth control pills, are pregnant, have an infection, or have recently had a trauma or injury.
If you have a dural sinus thrombosis, a blood clot in the dural sinuses which are channels found around your brain, it might be due to a recent infection. Specifically, infections like meningitis, which is an inflammation of the membranes around your brain and spinal cord, brain abscess, a pocket of pus in your brain caused by infection, or other infections in your central nervous system (CNS), the part of your body that includes your brain and spinal cord, might cause a blood clot to form in the veins surrounding your brain.
Risk Factors and Frequency for Venous Sinus Thrombosis
Despite being relatively rare, venous sinus thromboses (VST) do occur. Roughly, the incidence of it ranges from 13.2 to 15.7 cases per million patient-years. It’s more commonly seen in females, with the female-to-male ratio varying quite a bit – from 3:1 in some studies, down to an even 1:1 in others. On average, this condition shows up in people in their 4th or 5th decade of life, but can also occur earlier. VST is more likely to occur in patients who have health conditions making them predisposed to other forms of venous clots. Such conditions include issues like clotting disorders (thrombophilias), acute cancers, nephrotic syndrome, and even COVID-19.
Signs and Symptoms of Venous Sinus Thrombosis
Venous sinus thrombosis is a condition where there’s a blood clot in the brain’s venous sinuses. The key symptom is usually a headache. Other symptoms can depend on where the clot is, its size, and how severe it is. Some common signs include:
- Seizure
- Mental confusion or altered mental status
- Sudden sharp headache followed by other neurological symptoms such as seizures
- Raised pressure within the skull causing worse headaches when lying down, pulsating noise in the ears, and brief blurry vision
Patients presenting these features often do not have a history of certain medications and do not fit the typical profile of those who suffer from high pressure within the skull without a clear cause, often seen in young, overweight women. In these patients, there is often swelling at the back of the eye (optic nerve edema) when examined. An indication of increased pressure inside the skull is the absence of certain observable movements in the veins at the back of the eye.
Another type of sinus thrombosis can happen in the cavernous sinus in the brain, which often leads to problems with the third, fourth, fifth, and sixth cranial nerves. These issues usually happen all at once and can affect the eyes. This type of sinus thrombosis often happens because of an infection, most often related to the eyes, sinuses, or teeth.
Testing for Venous Sinus Thrombosis
The process for figuring out if someone has venous sinus thrombosis, which is a condition where a blood clot forms in the brain’s venous sinuses, often involves three main types of imaging. These include magnetic resonance imaging (MRI), magnetic resonance venography or computed tomogram (CT) venography.
An MRI is usually the first step as it can show the clot’s location depending on the clot’s age or breakdown phase. The MRI can also identify areas of localized swelling and internal brain bleeding. Furthermore, MRI can reveal areas of limited diffusion and lower apparent diffusion coefficient values, which indicate limited blood flow; this could mean that a clot is present. However, MRI is not the most precise tool for diagnosing venous sinus thrombosis.
On the other hand, techniques like magnetic resonance venography and CT venography provide a more specific and exact visualization of your brain’s veins, making them more sensitive for detecting the clot.
When a CT scan without contrast is performed, a typical sign of venous sinus thrombosis is an area of high density in the sinus regions, due to the clot being denser than flowing blood. However, non-contrast CT scans are not highly sensitive, and may only pick up the condition about one-third of the time. The addition of contrast in CT venography improves the visualization of the clot. A commonly noted feature is the ’empty delta sign’, where the clot appears dark due to lack of blood flow, while the surrounding areas appear bright.
With MRI imaging, the clot initially appears similar in color to the surrounding tissue on T1-weighted imaging, and these images become more intense as the clot’s contents change. On T2-weighted images, the clot appears darker. MRI can provide an effective visual representation of the clot using time of flight or gadolinium enhancement.
In addition to imaging, routine blood tests are needed, such as complete blood count, prothrombin time (a measure of how long it takes your blood to clot), activated partial thromboplastin time (another clotting measure), and international normalized ratio (a measure of blood clotting time). Doctors will also consider your medical history and look for conditions that might predispose you to blood clots. If these aren’t initially apparent, additional tests may be conducted to identify any hidden diseases or inherited conditions that increase blood clot risk, like factor V Leiden. Normal levels of D-dimer, a protein fragment involved in blood clotting, might indicate a lower likelihood of having venous sinus thrombosis. However, it’s also possible to have this condition even with normal D-dimer levels.
Treatment Options for Venous Sinus Thrombosis
Dural sinus thrombosis refers to the formation of a blood clot in the veins of the brain. Treating this condition involves two main steps. Firstly, treating the clot itself and the factors that may have led to its formation. Then, treating any subsequent medical problems that the clot may have caused.
The most frequent treatment for the blood clot is an anticoagulant, a medication that helps prevent blood clots. Depending on the severity of the condition, more robust treatments to dissolve the clot might be needed. These include thrombolytic therapy, which uses medicine to break up clots, and thrombectomy, a kind of surgery or procedure to remove the clot.
Guidelines from medical organizations like the American Heart Association suggest using an anticoagulant called heparin when the condition is first diagnosed. Several studies show that patients who received this medication shortly after being diagnosed had a lower risk of dying and better long-term health outcomes. The decision to use this treatment can be complex, due to common occurrence of brain hemorrhage (bleeding inside the brain). However, it’s important to note that these studies did not exclude patients with brain hemorrhages from receiving anticoagulation and the deaths in these studies were not due to bleeding or worsening of existing brain bleeds.
Patients with this condition should keep using anticoagulant medication for three to six months if the clot was provoked by certain conditions like pregnancy, injury, or infection. If the clot was unprovoked or happened alongside other blood clot events, they may need to keep using the medication for six to twelve months. If the patient has a tendency for blood clotting or other venous thromboembolic events have occurred, doctors should consider lifelong anticoagulation. Treating blood clots directly is not yet widely recommended, but it can be beneficial in some cases. It is typically reserved for patients whose condition doesn’t improve as expected, putting them at risk of other problems like vision loss.
Finally, it’s essential to treat any complications that might arise from the blood clot, as blood clots in the veins can lead to many complications. For example, the clot may cause abnormally high pressure in the patient’s brain, which may need to be medically lowered with medications like acetazolamide or other procedures. If this condition causes severe pressure in the brain, surgeries like decompressive craniectomy, which reduces pressure on the brain by removing part of the skull, can be performed. Patients with seizures following dural sinus thrombosis may need to use antiepileptic medications.
What else can Venous Sinus Thrombosis be?
Doctors need to consider several alternatives when diagnosing certain variants of medical conditions. The conditions they might need to rule out are:
For the Encephalopathy variant:
- Metabolic derangement
- Medication side effects
- Delirium
- Dementia
- Stroke
- Sepsis
- Demyelinating processes
For the Focal deficit variant:
- Stroke
- Hemorrhage stroke
- Meningitis
- Tumor
- Multiple sclerosis
- Seizure disorder
For the Papilledema variant:
- Idiopathic intracranial hypertension (IIH)
- Meningitis
- Tumor
These are just possible conditions that the doctor might need to rule out to arrive at an accurate diagnosis.
What to expect with Venous Sinus Thrombosis
If properly diagnosed and treated, Vein Sinus Thrombosis (VST), a condition where blood clots form in the brain’s veins, generally has positive outcomes. In an international study on this condition, about 57% of patients didn’t experience any lasting symptoms or issues even after 16 months on average from initial treatment.
In the same study, however, approximately 2% of patients had serious issues due to the condition, and sadly, 8% of patients passed away. Despite those rather worry-worthy figures, do keep in mind that most people with this condition fare well with proper treatment and management.
Possible Complications When Diagnosed with Venous Sinus Thrombosis
Common complications from venous sinus thromboses are serious and varied. They can include:
- Headache
- Visual loss (This is caused by optic neuropathy due to something called papilledema)
- Stroke
- Seizure
- Subarachnoid hemorrhage (bleeding in an area of your brain)
- Subdural hemorrhage (bleeding on the surface of your brain)
- Intraparenchymal hemorrhage (bleeding inside your brain)
Venous sinus thromboses is a serious medical condition and these complications may have varying impacts on health.
Preventing Venous Sinus Thrombosis
If a patient has a condition called thrombophilia, which makes their blood more likely to clot, long-term use of blood-thinning medication can help decrease the chance of a recurring blood clot in the veins of the brain (VST). Patients should be well-informed about why it’s crucial to continue this medication. The decision to use this medication should be made together with the patient, taking into account how their clotting condition increases their risk. For example, there is a condition called antiphospholipid antibody syndrome which is known to significantly increase the chances of a recurring vein clot compared to other causes.
