Sphenoid sinus

The sphenoid sinus is the most posterior paranasal sinus.

Summary

• 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 the orbital branch of the pterygopalatine ganglion

Gross anatomy

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 hemisinuses 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 pneumatisation

Pneumatisation types have been subdivided ⁴:

• 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

Lymphatic 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 (CN II) 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

Pneumatisation of the sphenoid sinus 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 pneumatisation of this sinus and to report its relationship with adjacent neurovascular structures, especially the presence of dehiscence. In particular, the close proximity of the optic canal and carotid canal to the sphenoid sinus are important aspects to consider when planning sphenoid sinus surgery.⁵

See also

• trans-sphenoidal hypophysectomy