The sphenoid sinus is the most posterior paranasal sinus. It lies antero-inferior to the sella. It is important to look for the variable pneumatization of this sinus and to report the relationship with neurovascular structures.
Pneumatization starts at around 2 year of age and it develops more slowly than the other paranasal sinuses.
The sphenoid sinus is formed within the body of the sphenoid, communicating with the roof of the nasal cavity via the spheno-ethmoidal recess in its anterior wall.
- superiorly: cavernous sinus, sella turcica and its contents
- inferiorly: nasal cavities
- anteriorly: nasal cavities
- posteriorly: contents of the middle cranial fossa, posterior ethmoidal sinus
- laterally: cavernous sinus, cranial cavity
Types of pneumatization
- lateral recess
- sellar (which can be incomplete or complete)
- arterial supply: posterior ethmoidal artery, nasal branches of the sphenopalatine artery
- venous drainage: superior ophthalmic veins via posterior ethmoidal veins
Lymph drainage occurs via afferent vessels leading into the retropharyngeal nodes.
- parasympathetic: orbital branches of the pterygopalatine ganglia
- sensory: posterior ethmoidal nerve from the nasociliary nerve, a branch of the ophthalmic division of the trigeminal nerve
With respect to optic nerve relationship:
- type 1: adjacent to sphenoid sinus
- type 2: indenting the sinus
- type 3: traversing the sinus
- type 4: adjacent to posterior ethmoid sinus