Cavernous sinus thrombosis

Cavernous sinus thrombosis is defined by clotting in the cavernous sinus, part of the skull at the base of the brain through which deoxygenated blood drains into veins. It's most often caused by an infection, usually staphylococcus or streptococcus. It's often fatal, even with treatment, and progresses rapidly.
In most cases, an infection in the nasal passages or the teeth spreads to the cavernous sinus. Rarely, an infection develops in the sinus itself.
The condition is not easy to diagnose as many conditions can cause these symptoms, although they are much more severe and progress more rapidly in CST. A definitive diagnosis can usually be established with radiological imaging. One of the defining characteristics is palsy spreading from one eye. Blood cultures are often necessary to establish the exact infection, although antibiotics should be started immediately. Meningitis, which is far more common, should be ruled out.
With proper treatment, including surgical drainage if necessary, the mortality rate is usually about 20%. Early diagnosis and treatment increases the patient's changes significantly.
Cavernous sinus thrombosis at Wikipedia