The danger triangle of the face is a triangle with
two corners at both corners of the mouth and one corner in the middle
of the nose between the eyes. The way the blood flows
to the human nose is special, so it is possible (but not likely) for infections to
spread directly to the brain from a cut, scratch or a popped pimple.
The path this infection would take would be back up the
wrong way of a vein (called the ophthalmic veins) that runs from an
empty hollow in the middle of the head at the bottom of the skull called the
cavernous sinus. The cavernous sinus lies partly inside the skull, under the
layers of protection against infection. The cavernous sinus is a way a lot of
blood flows away from the brain back down the neck.
Many people wrongly assume that the veins of the
head do not contain one-way valves like other veins of the circulatory system.
In fact, almost all people, but not all, have valves in the veins of the face. But
even with one way valves, blood flow between the facial vein and cavernous
sinus can spread infection from the face; it is the direction of blood flow
that is important.
