Expansion
Nose to the mouth's two corners, no valves, straight line to the cavernous sinus
Mnemonic
“The triangle from the corners of the mouth to the bridge of the nose”.
The facial vein is valveless, and communicates with the cavernous sinus through:
- The superior ophthalmic vein, via the angular vein
- The deep facial vein to the pterygoid plexus, and thence by emissary veins
Infection in this area, classically from squeezing a boil of the upper lip or nose, can therefore travel against the direction of flow into the skull, causing cavernous sinus thrombosis.
The signs are a proptosed, chemotic, painful eye with an early sixth nerve palsy, because the abducens nerve lies free within the sinus, followed by III, IV, V1 and V2 in the lateral wall.
Expansion
- Triangle boundaries - bridge of the nose to both corners of the mouth
- Facial vein - lacks valves in this region
- Risk - direct spread to the cavernous sinus