Sphenoid sinus

Dr Daniel J Bell ◉ and Dr Ayush Goel et al.

The sphenoid sinus is the most posterior paranasal sinus.

The sphenoid sinuses are paired spaces formed within the body of the sphenoid bone, communicating with the roof of the nasal cavity via the sphenoethmoidal recess in its anterior wall. The two sinuses are separated by a septum which may or may not be in the midline. It usually lies anteroinferior to the sella.

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.

Relations

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

conchal
lateral recess
presellar
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

Lymphatic drainage

Lymph drainage occurs via afferent vessels leading into the retropharyngeal nodes

Innervation

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

Variant anatomy

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

Development

Pneumatization starts at around 2 years of age and it develops more slowly than the other paranasal sinuses.

Practical points

It is important to look for and report the type of pneumatization of this sinus and to report the relationship with adjacent neurovascular structures, especially dehiscence