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 a few 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.

In very rare cases, cavernous sinus thrombosis can occur after having some types of coronavirus (COVID-19) vaccine. If this happens, symptoms can appear between 4 days and 4 weeks after vaccination.

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 of cavernous sinus thrombosis include:

• a high temperature
• 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.

Call 111 immediately if you experience:

• a severe headache that is not relieved with painkillers or is getting worse
• a headache that feels worse when you lie down or bend over
• a headache that's unusual for you and occurs with blurred vision, feeling or being sick, problems speaking, weakness, drowsiness or seizures (fits)
• eye pain or swelling of one or both eyes
• a rash that looks like small bruises or bleeding under the skin
• shortness of breath, chest pain, leg swelling or persistent abdominal (tummy) pain

While it's highly unlikely to be caused by a cavernous sinus thrombosis, these symptoms need further investigation.

In very rare cases, these symptoms may appear from around 4 days to 4 weeks after being vaccinated with the coronavirus (COVID-19) vaccine.

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