The sphenoid sinus lies posterior to the nasal cavity, just superior to the nasopharynx. It is usually divided by a septum near the midline into a right and left side. The optic nerve, the carotid artery, and the cavernous sinus run just lateral to the sphenoid sinus, and can be at risk in severe sphenoid infections. In some cases the bony separation between these structures can be dehiscent.