Cavernous sinus thrombosis is usually caused by a bacterial infection that spreads from another area of the face or skull.

About 7 in every 10 cases are the result of an infection of staphylococcal (staph) bacteria, which can cause:

• sinusitis – an infection of the small cavities behind the cheekbones and forehead
• a boil – a painful pus-filled swelling or lump that develops on the face (attempting to squeeze a boil can increase the risk of the infection spreading)

Most people have one of these conditions before developing cavernous sinus thrombosis. However, boils and sinusitis are common and it is very rare that they lead to cavernous sinus thrombosis.

Blood clot

In most cases of cavernous sinus thrombosis, a blood clot forms in the cavernous sinuses to try to prevent bacteria spreading further into the body. This is known as thrombosis.

However, the clot usually blocks the flow of blood away from the brain. This increases the pressure in the cavernous sinuses and can cause damage to the brain, eyes and central nervous system.

In addition, the blood clot is often unable to prevent the spread of infection. If the condition is left untreated, the infection can spread through the bloodstream, causing blood poisoning (sepsis).

Other causes

Less commonly, a blood clot can develop in the cavernous sinuses due to:

• a severe head injury
• an infection spreading from the teeth or gum (dental abscess)
• a fungal infection
• a health condition or other underlying factor that makes you more prone to blood clots, the most common being pregnancy
• conditions that cause inflammation (swelling) inside the body, such as lupus or Behçet’s disease
• some types of medication, such as the contraceptive pill, although this is very rare

About one in three people with cavernous sinus thrombosis die, and many people who survive it go on to develop further problems.

The condition leads to long-term symptoms in around 1 in 10 people, including seizures (fits) and severe headaches.

Vision problems

Problems with vision are also a relatively common complication of cavernous sinus thrombosis. About one in six people experience some degree of permanent visual impairment.

However, permanent blindness is less common, affecting around 1 in 160 people.

Blood clots

There is a risk that another blood clot may develop elsewhere in the body, for example:

• the legs – this is known as deep vein thrombosis and affects around 1 in 40 people
• the lungs – this is known as a pulmonary embolism and affects around 1 in 200 people
• the brain – this triggers a stroke and affects around 1 in 330 people

These conditions are very serious and can be fatal.

Infection

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

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

Both of these conditions are very serious and can be fatal, especially if they’re not treated promptly.

Cavernous sinus thrombosis is a rare and life-threatening condition in which a blood clot develops in the cavernous sinuses.

The cavernous sinuses are a series of hollow spaces located under the bottom of the brain, behind each eye socket. A major blood vessel called the jugular vein carries blood through the cavernous sinuses away from the brain.

Symptoms of a cavernous sinus thrombosis include:

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

Read more about the symptoms of cavernous sinus thrombosis.

When to see your GP

You should always contact your GP if you are experiencing a persistent and severe headache you have not had before, or if you develop swelling of the eyes or severe eye pain.

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.

After an examination of your symptoms, you may be referred for several tests, including a computerised tomography (CT) scan, a magnetic resonance imaging (MRI) scan and blood tests.

Why does cavernous sinus thrombosis happen?

Most cases of cavernous sinus thrombosis occur when a bacterial infection in another part of the skull or face spreads into the cavernous sinuses.

In around 7 out of every 10 cases, staphylococcal (staph) bacteria, which can cause sinusitis and boils, is responsible. It often appears a few days before cavernous sinus thrombosis.

A blood clot then forms inside the cavernous sinuses in an attempt to prevent the infection from spreading further into the body.

This blood clot places the brain under increasing pressure by restricting the blood flow, which can damage the brain, eyes and central nervous system.

Read more about the causes of cavernous sinus thrombosis.

How is cavernous sinus thrombosis treated?

Cavernous sinus thrombosis needs treatment in hospital.

The main treatment for the condition is antibiotics, which are normally given through a drip into a vein in the arm. This treatment usually lasts at least three to four weeks.

Despite some uncertainty about their use, you may also be given additional treatment with anticoagulant medication (to dissolve and prevent blood clots) or steroid medication (to reduce any swelling).

Most people will need to stay in hospital for several weeks or even months before they are well enough to go home.

Read more about treating cavernous sinus thrombosis.

Complications

Cavernous sinus thrombosis is an extremely serious condition. Even with prompt treatment, as many as one in three people with the condition die.

Around 1 in 10 people who survive will develop long-term health problems as the result of damage to their brain, such as persistent headaches and fits, or some degree of visual impairment. 

Read more about the complications of cavernous sinus thrombosis. 

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.

Symptoms often start within five to 10 days of developing an infection in the face or skull, such as sinusitis or a boil.

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

The eyes

In most cases of cavernous sinus thrombosis, the eyes are affected. You may experience:

• swelling and bulging of the eyes – this normally starts in one eye and spreads to the other eye within 24 to 48 hours 
• redness of the eyes
• eye pain, which can be severe
• vision problems, such as double vision or blurred vision
• difficulty moving the eyes
• drooping of the eyelids

Other symptoms

Other symptoms of cavernous sinus thrombosis include:

• a high temperature of 38°C (100.4°F) or above
• being sick (vomiting)
• seizures (fits)
• changes in your mental state, such as feeling very confused

These usually occur if cavernous sinus thrombosis is left untreated or if an infection causing the condition spreads throughout the body.

Without treatment, most people with cavernous sinus thrombosis will become increasingly drowsy and eventually 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.

Cavernous sinus thrombosis is a serious condition that needs to be treated in hospital. 

In most cases, you will be treated in an intensive care unit so your condition can be closely monitored.

Antibiotics

The main treatment for cavernous sinus thrombosis is antibiotic medication. This is started as soon as possible, even before tests have confirmed if a bacterial infection is responsible for the condition.

If tests later show that a bacterial infection did not cause the condition, antibiotic treatment may stop.

Most people will require at least a three- to four-week course of antibiotics to ensure the infection has been fully cleared from their body. These are given through an intravenous drip directly connected to one of your veins.

Around 1 in 10 people will experience side effects when taking antibiotics. These are generally mild and can include diarrhoea, nausea and a skin rash.

Anticoagulants

In some cases, you may also be given a medication called heparin to help dissolve the clot and prevent further clots. Heparin is an anticoagulant, which means it makes the blood less sticky.

However, there are some doubts about the use of anticoagulant treatment for cavernous sinus thrombosis, such as when it should be used and how long treatment should last. There is also a risk of serious problems such as excessive bleeding (haemorrhaging).

There is a lack of evidence concerning the use of anticoagulants for the condition because it is so rare that it is difficult to study. Nevertheless, the little research that does exist seems to suggest that anticoagulants can be an effective treatment for some people, and most doctors agree it should be used where appropriate. 

Corticosteroids

You may also be given steroid medication (corticosteroids) in addition to antibiotics. Corticosteroids can help reduce the level of inflammation and swelling in your body.

However, as with anticoagulant therapy, there is little evidence concerning the effectiveness of corticosteroids in treating cavernous sinus thrombosis. Nonetheless, corticosteroids are thought to be beneficial for some people.

Surgical drainage

If the symptoms of cavernous sinus thrombosis were caused by an infection spreading from a boil or sinusitis, it may be necessary to drain away pus from that site. This can be done either using a needle or during surgery.

Read more about treating abscesses.