Cavernous sinus thrombosis


Cavernous sinus thrombosis is a blood clot in the cavernous sinuses. It can be life-threatening.

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

A blood clot can develop when an infection in the face or skull spreads to the cavernous sinuses. The blood clot develops to prevent the infection spreading further, but it can restrict the blood flow from the brain, which can damage the brain, eyes and nerves running between them. Sometimes, clots can develop without infection.

Read more about the causes of cavernous sinus thrombosis.

Symptoms of cavernous sinus thrombosis include:

  • a sharp and severe headache, particularly around the eye
  • swelling and bulging of the eye(s) and the surrounding tissues
  • eye pain that's often severe
  • double vision

Read more about the symptoms of cavernous sinus thrombosis.

When to see your GP

Contact your GP if you experience a persistent and severe headache you haven't had before, or if you develop eye pain or swelling of one or both eyes.

While it's highly unlikely to be the result of cavernous sinus thrombosis, a persistent headache usually needs to be investigated.

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

Treating cavernous sinus thrombosis

Cavernous sinus thrombosis needs treatment in hospital.

In most cases, you'll be treated in an intensive care unit, so you can be closely monitored.


Antibiotics are the main treatment for cavernous sinus thrombosis. Treatment will be started as soon as possible, even before tests have confirmed if a bacterial infection is responsible.

If tests later show that a bacterial infection didn't cause the condition, antibiotic treatment may be stopped.

Most people will require antibiotics for a few weeks to ensure the infection has been fully cleared from their body. The antibiotics will be given through an intravenous drip directly connected to one of your veins.

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


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

Some people also need to take anticoagulant tablets for a few months or longer after leaving hospital.


Some people are also given steroid medication (corticosteroids). Corticosteroids can reduce inflammation and swelling in your body.

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.

How long does treatment last?

Several weeks of antibiotic treatment are usually necessary to ensure the infection has cleared. However, it can take a long time to recover fully, and it may be several months before you're well enough to leave hospital.

Complications of cavernous sinus thrombosis

Cavernous sinus thrombosis is a very serious condition. Even with prompt treatment, as many as 1 in 3 people with the condition may die.

Some people who survive will develop long-term health problems due to damage to their brain, such as persistent headaches and fits, or some degree of vision loss.

Who's affected?

It's difficult to say exactly how many people are affected by cavernous sinus thrombosis, but it's thought to be very rare.

The condition affects people of all ages and tends to be more common in women than men. This may be because pregnancy and taking the oral contraceptive pill can make women more vulnerable to blood clots.


The most common initial symptom of 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 5 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 usually starts in one eye and spreads to the other eye soon after
  • red 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 38C (100.4F) or above
  • vomiting
  • seizures (fits)
  • changes in mental state, such as feeling very confused

These symptoms 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 have a persistent and severe headache that you've never had before.

While it's highly unlikely to be caused by a cavernous sinus thrombosis, a persistent headache usually requires further investigation.

You should also contact your GP if you develop any of the eye symptoms described above.

Who can get it

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

Many 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
  • boil – a red, painful lump that develops at the site of an infected hair follicle (squeezing 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's 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, which increases the pressure in the cavernous sinuses and can damage the brain, eyes and the nerves running between them.

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:

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

The cavernous sinuses

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

Each forms a major vein that is part of a network of sinuses that eventually drain into the jugular veins, which carry blood away from the brain.


Up to 1 in 3 people with cavernous sinus thrombosis may die. Some people who survive it are left with ongoing symptoms such as seizures (fits) and severe headaches.

It can also cause further problems with vision, blood clots and infections.

Vision problems

Problems with vision are a relatively common complication of cavernous sinus thrombosis.

A few people have a degree of permanent visual impairment although permanent blindness is uncommon.

Blood clots

There's also a risk that another blood clot may develop elsewhere in the body – for example, in the:

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

These conditions are very serious and can be fatal.


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

  • meningitis – an infection of the outer protective layer of the brain that 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, particularly if they're not treated promptly.

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website
Last Updated: 05/07/2021 12:45:36