A cavernous sinus thrombosis is a rare and life-threatening condition in which a blood clot develops in a part of the skull called the cavernous sinuses (see below).

Symptoms of a cavernous sinus thrombosis include:

• a sharp and severe headache
• swelling of the eyes
• eye pain that is often severe

Read more about the symptoms of cavernous sinus thrombosis.

You should contact your GP straight away if you experience any of these symptoms.

The cavernous sinuses

The cavernous sinuses are a series of hollow spaces located under the bottom of the brain, behind each eye socket.

Running through the sinuses is a major blood vessel called the jugular vein whose role is to carry blood away from the brain and back to the heart and lungs.

When to see your GP

You should always contact your GP if you are experiencing a persistent and severe headache that you have not had before.

While it is highly unlikely to be the result of a cavernous sinus thrombosis, a persistent headache is a symptom that usually requires further investigation.

You should also contact your GP if you develop swelling of the eyes or severe eye pain.

Causes

Most cases of cavernous sinus thrombosis are caused when a bacterial infection (or much less commonly, a fungal infection) in another part of the skull spreads into the cavernous sinuses.

The immune system, which is the body’s defence against infection, will then create a blood clot inside the cavernous sinuses to prevent the infection from spreading.

The blood clot can then place the brain under increasing pressure, which can damage the brain and, without treatment, will inevitably prove fatal.

Read more about what causes cavernous sinus thrombosis.

Treatment

The main treatment for cavernous sinus thrombosis is antibiotics, which are normally provided through a drip that is directly connected to a vein in the arm.

Most people will need to stay in hospital for 3-4 weeks before they are well enough to leave.

Read more about the treatment of cavernous sinus thrombosis.

Who is affected by cavernous sinus thrombosis?

Cavernous sinus thrombosis is a very rare condition. One study estimated that only 1 in every 2.5 million people in England will develop cavernous sinus thrombosis in any given year.

The condition is three times more common in women than men. It is thought that the two main reasons for this are that pregnancy and taking the oral contraceptive pill can make women more vulnerable to blood clots.

Younger adults and children are more likely to be affected by a cavernous sinus thrombosis than older adults.

Outlook

Cavernous sinus thrombosis is an extremely serious condition and even with prompt treatment as many as one in three people with the condition will die from related complications.

Around one in ten people who do survive will develop long-term health problems as the result of damage to their brain, such as persistent headaches and fits. Read more about the complications of cavernous sinus thrombosis. 

Contagious

Contagious is when a disease or infection can be easily passed from one person to another.

Inflammation

Inflammation is the body's response to infection, irritation or injury. It causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Tissue

Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.

Vein

Veins are blood vessels that carry blood back to the heart from the rest of the body.

The most common initial symptom of a cavernous sinus thrombosis is a headache. This usually develops as a sharp pain, located behind or around the eyes, that steadily gets worse over time.

Occasionally, some people get what is known as a thunderclap headache, which is a sudden severe headache that comes out of nowhere.

It can be several days or even weeks before additional symptoms develop after the headache starts.

The eyes

Normally the eyes are the first to be affected by additional symptoms following the headache.

You may experience:

• Swelling of the white sections of your eyes. The swelling normally starts in one eye and then spreads to the other eye within 24-48 hours. 
• Redness of the eyes.
• Eye pain and an uncomfortable feeling of your eyes being heavy and full.
• Problems with your vision, such as double vision.
• Difficulty controlling the movement of your eyes.
• Enlarged pupils (the hole in the centre of the eye).
• Drooping of your lower or upper eyelid.

Other symptoms

If cavernous sinus thrombosis is left untreated then the pressure inside the skull can increase. If the condition is caused by a bacterial infection, the infection can spread throughout the body.

This can trigger a range of symptoms, such as:

• A high temperature of 38°C (100.4°F) or above.
• Seizures (fits).
• Changes in your mental state, such as feeling very confused or like you can’t be bothered to do anything (apathetic).
• Weakness on one or both sides of the body. This is caused by damage to the nerves you use to control the body rather than a weakness in your muscles.
• Problems with speech. Most people who develop this symptom can speak normally but their words make no sense. The medical term for this is aphasia.

Without treatment most people with cavernous sinus thrombosis will become increasingly drowsy and then fall into a coma.

When to seek medical advice

You should always contact your GP if you are experiencing a persistent and severe headache that you have never had before.

While it is highly unlikely to be the result of a cavernous sinus thrombosis, a persistent headache is a symptom that usually requires further investigation.

You should also contact your GP if you develop any of the symptoms affecting the eyes that are described above.

Coma

A coma is a sleep-like state when someone is unconscious for a long period of time.

The most common cause of cavernous sinus thrombosis is when an infection in another part of the skull, such as the eye, nose or ears, spreads into the cavernous sinuses.

The two infections most commonly associated with a cavernous sinus thrombosis are:

• sinusitis, which is an infection of the small, air-filled cavities behind the cheekbones and forehead
• a boil, which is a large painful pus-filled swelling or lump that develops on the face

Attempting to squeeze a boil can sometimes result in an infection spreading into the cavernous sinuses.

The immune system will create a blood clot to prevent the infection from spreading further into the body.

However, the clot will usually block the flow of blood away from the brain through the jugular vein. This blockage increases the pressure on the brain and blood can also flow back up into the brain, both of which can damage the brain, as well as the eyes and the central nervous system.

In addition, the immune system, despite the blood clot, is normally ineffective in preventing the spread of infection out of the skull and into the rest of the body.

So the infection often spreads through the blood stream causing multiple organ failure, which is known as blood poisoning or sepsis.

Other causes

Other less common causes of cavernous sinus thrombosis include:

• A severe head injury that results in a blood clot. This is thought to be the second most common cause.
• An infection spreading from a tooth or gum infection .
• Having a health condition or other underlying factor that makes you more prone to blood clots - the most common being pregnancy.
• People who have conditions that cause inflammation (swelling) inside their body, such as lupus or Behçet’s disease, can occasionally develop blood clots.
• Some types of medication, such as the contraceptive pill or the medications used in hormone replacement therapy, can cause blood clots as a side effect, though this is very rare.

Bacteria

Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some are good for you.

To confirm that you have cavernous sinus thrombosis, your GP may refer you to have the tests described below.

• A lumbar puncture, where a sample of fluid is taken from your spinal cord. This may show signs of infection. 
• A computerised tomography (CT) scan of your sinuses, eyes and brain. X-rays build up a detailed picture of your head to rule out other causes, such as an abscess.
• A magnetic resonance imaging (MRI) scan of your brain. A magnetic field and radio waves build up a detailed picture of your brain.

If it is thought that an infection is responsible for your symptoms your GP will take a sample of your blood and samples of fluid, mucus or pus from your throat and nose to send to the laboratory for testing.

X-ray

An X-ray is a painless way of producing pictures of inside the body using radiation.

Cavernous sinus thrombosis is a serious condition. If it’s suspected you will be immediately admitted to hospital. Depending on your general state of health this may be to a regular ward or to an intensive care unit.

You will be given a combination of different antibiotics through a drip that is directly connected to one of your veins.

Most people will require at least a 3-4 week course of antibiotics to ensure that the infection has been fully cleared from their body.

Around 1 in 10 people will experince side effects when taking antibiotics. These are generally mild and include:

• diarrhoea
• nausea
• skin rash
• hardening of the skin at the point where the drip goes into your vein

In some cases you may also be given a medication called heparin to help dissolve the clot and /or prevent further clots.

Heparin makes the blood less sticky.

You may also be given steroid medication (corticosteroids) to help reduce levels of inflammation and swelling in your body.

If the symptoms of cavernous sinus thrombosis were due to an infection spreading from a boil or sinusitis, then it may be necessary to drain away pus from that site.

This can be done using a needle or during surgery. Read more about treating abscesses.

Even if you respond well to treatment it may be several months before you are well enough to leave hospital.

Antibiotic

Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. Examples of antibiotics include amoxicillin, streptomycin and erythromycin.

The two most common complications of cavernous sinus thrombosis occur after the infection has passed. These are:

• seizures (fits), which affect around 1 in 10 people
• severe headaches, which also affect around 1 in 10 people

Less commonly, once the infection has passed, another blood clot may occur somewhere else in the body. For example this could be in:

• the legs, which is known as deep vein thrombosis, and affects around 1 in 40 people
• the lungs, which is known as a pulmonary embolism, and affects around 1 in 200 people
• the brain, which would trigger the potentially fatal condition known as a stroke, and affects around 1 in 330 people

Permanently severe visual impairment is another less common long-term complication affecting around 1 in every 160 people.

Complications can also occur if the infection spreads from beyond the cavernous sinuses. These include:

• meningitis, which is an infection of the outer protective layer of the brain and can cause symptoms such as stiff neck, mental confusion and sensitivity to light
• sepsis or blood poisoning, which can cause symptoms such as chills, fast heartbeat and rapid breathing
• blindness