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 7in 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 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 rarethat 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 clotusually blocks the flow of blood away from the brain, which increases the pressurein the cavernous sinuses andcan 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 bloodclot candevelop in the cavernous sinuses, due to:

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