Cavernous sinus thrombosis - Causes of cavernous sinus thrombosis

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