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. The sinus is often divided by a central septum, and in this context some radiologists employ the term sphenoid hemisinus for each portion.
Pneumatization starts at around 2 year of age and it develops more slowly than the other paranasal sinuses.
- 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 ganglion
- 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