The sphenoid sinus is the most posterior paranasal sinus. It lies anteroinferior 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.
- location: the central body of the sphenoid bone anteroinferior to the sella turcica
- blood supply: posterior ethmoidal and sphenopalatine arteries
- innervation: posterior ethmoidal nerve and orbital branch of pterygopalatine fossa
The sphenoid sinuses are paired spaces formed within the body of the sphenoid bone, communicating with the roof of the nasal cavity via the spheno-ethmoidal recess in its anterior wall. The two sinuses are separated by a septum which may or may not be in the midline.
A large sinus can show a number of ridges and depressions related to closely adjacent structures. These can include the pituitary gland, optic nerve and internal carotid artery.
- superiorly: cavernous sinus, sella turcica and its contents
- inferiorly: nasal cavities
- anteriorly: nasal cavities, posterior ethmoid air cells
- posteriorly: contents of the middle cranial fossa
- 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