The other, disseminated intravascular coagulation (DIC), involves blood clots forming throughout the body.
These conditions are very rare however. In a city of one million people, scientists would expect only five cases a year.
During a US study of the AstraZenca vaccine, an independent data safety monitoring board (DSMB) conducted a specific review of cerebral venous sinus thrombosis (CVST).
The DSMB found no increased risk of thrombosis among the 21,583 participants receiving at least one dose of the vaccine. There were no cases of CVST in the trial.
What is Cerebral Venous Sinus Thrombosis?
Cerebral Venous Sinus Thrombosis (CVST) is a rare form of stroke affecting about five people per million yearly.
It occurs when a blood clot forms in the brain’s venous sinuses, preventing blood from draining out.
What are the symptoms of Cerebral Venous Sinus Thrombosis
Blood cells may break and leak blood into the brain tissues, causing a haemorrhage. The condition can lead to headaches, abnormal vision and similar symptoms to stroke such as weakness of the face and limbs on one side of the body, seizures, coma and death.
Vaccinated Britons have been urged to seek medical attention if they develop a four-day headache or unexpected bruising after receiving the AstraZeneca jab.
Who is most at risk?
Risk factors for adults include pregnancy, cancer, obesity and problems with blood clotting.
It can occur even in newborns and babies in the womb.
People who have had any type of stroke recover best the sooner they are treated.
The NHS recommends that anyone who suspects they or another person may be suffering a stroke should seek medical aid immediately.
What is the treatment for CVST?
Treatments include anticoagulant blood thinners such as warfarin, anti-seizure medicine, fluids or surgery.
When was CVST first identified?
CVST was a diagnosis generally made after death until the latter half of the 20th century.
In the 1940s, doctors learned to recognise the characteristic symptoms, and used lumbar punctures to diagnose the condition.