[1][2] : 345–346  Due to the special nature of the blood supply to the human nose and surrounding area, it is possible for retrograde infection from the nasal area to spread to the brain, causing cavernous sinus thrombosis, meningitis, or brain abscess.

The cavernous sinus lies within the cranial cavity, between layers of the meninges, and is a major conduit of venous drainage from the brain.

Thus, it is not the absence of venous valves but rather the existence of communications between the facial vein and cavernous sinus and the direction of blood flow that is important in the spread of infection from the face.

[5] In 1937, a study found that 61% of the cases of cavernous sinus thrombosis were the result of boils on the upper part of the face.

Failure of each of the nerves listed above will manifest in loss of function of the specific muscle, gland, or parasympathetic innervations (from CN III).