Sphenoid Sinus

The sphenoid sinuses are paired air-filled cavities located within the body of the sphenoid bone. They are the most posterior of the paranasal sinuses and occupy a central position within the skull base, posterior to the nasal cavity.

The sphenoid sinuses are anatomically important because they lie close to several major neurovascular and endocrine structures. The pituitary gland lies superiorly within the sella turcica, the cavernous sinuses and internal carotid arteries are related laterally, and the optic nerves and optic chiasm are closely related to the superior and superolateral region.

Location

The sphenoid sinuses are located within the body of the sphenoid bone, posterior to the nasal cavity and ethmoidal air cells.

They lie inferior to the sella turcica and central skull base and communicate anteriorly with the nasal cavity.

Sphenoid Bone

The sphenoid bone is a centrally positioned bone of the cranial base.

Its body contains the sphenoid sinuses and supports the sella turcica, which houses the pituitary gland.

Right and Left Sphenoid Sinuses

The body of the sphenoid usually contains right and left sphenoid sinuses separated by a bony intersinus septum.

The two cavities are commonly unequal in size and shape because the septum frequently deviates from the midline.

Intersinus Septum

The intersinus septum divides the sphenoid sinus into right and left compartments.

Its orientation is highly variable and it may attach eccentrically to the sinus walls, including regions near important neurovascular structures.

Shape and Size

The size and configuration of the sphenoid sinuses depend on the extent of pneumatization of the sphenoid bone.

Considerable variation exists between individuals and between the two sides of the same individual.

Walls and Relationships

The walls of the sphenoid sinus have important relationships with surrounding skull base structures.

• Superiorly, the sinus is related to the sella turcica, pituitary gland, optic chiasm, and structures of the middle cranial region.
• Laterally, it is related to the cavernous sinuses, internal carotid arteries, and cranial nerves associated with the cavernous sinus.
• Anteriorly, it is related to the posterior nasal cavity and sphenoethmoidal recess.
• Posteriorly, it approaches the clival region.
• Inferiorly, it is related to the roof of the nasopharynx and sphenoidal rostrum region.

Superior Wall

The superior wall of the sphenoid sinus is closely related to the central skull base.

Its posterior superior portion lies beneath the sella turcica, while more anterior and lateral portions may have close relationships with the optic apparatus.

Sella Turcica

The sella turcica is a saddle-shaped depression on the superior surface of the sphenoid body.

Its central depression, the hypophyseal fossa, contains the pituitary gland and lies immediately superior to a well-pneumatized sphenoid sinus.

Pituitary Gland Relationship

The pituitary gland occupies the hypophyseal fossa above the sphenoid sinus.

This relationship provides the anatomical basis for transsphenoidal surgical approaches to the pituitary gland through the nasal cavity and sphenoid sinus.

Optic Chiasm Relationship

The optic chiasm lies superior to the sphenoid region and anterior to the pituitary stalk in its usual configuration.

The extent of sphenoid pneumatization influences the thickness of bone separating the sinus from neighboring optic structures.

Optic Nerve Relationship

The optic nerves course close to the superolateral aspects of the sphenoid sinus as they approach the optic canals.

In some individuals, extensive pneumatization causes the optic canal to produce a prominence in the sinus wall, and the intervening bone may be very thin.

Internal Carotid Artery Relationship

The cavernous segments of the internal carotid arteries lie lateral to the sphenoid sinus.

The arteries may create visible prominences in the lateral sinus walls, particularly when sphenoid pneumatization is extensive.

Cavernous Sinus Relationship

The cavernous sinuses lie on either side of the body of the sphenoid.

They are therefore closely related to the lateral walls of the sphenoid sinus and contain or are associated with several important cranial nerves and the internal carotid artery.

Cranial Nerve Relationships

The cavernous sinus region contains important cranial nerves related to ocular movement and facial sensation.

The oculomotor, trochlear, ophthalmic, and maxillary nerves are related to the lateral wall of the cavernous sinus, while the abducens nerve passes within the cavernous sinus close to the internal carotid artery.

Clivus

The clivus lies posterior to the sphenoid sinus and is formed by portions of the sphenoid and occipital bones.

The extent of posterior sphenoid pneumatization determines the relationship between the sinus cavity and clival bone.

Anterior Wall

The anterior wall of the sphenoid sinus faces the posterior nasal cavity.

Each sinus communicates with the nasal cavity through a sphenoidal ostium located in its anterior wall.

Sphenoidal Ostium

The sphenoidal ostium is the natural opening of the sphenoid sinus.

It is typically located high on the anterior sinus wall and opens into the sphenoethmoidal recess.

Sphenoethmoidal Recess

The sphenoethmoidal recess is a small space in the posterosuperior nasal cavity.

It lies superior and posterior to the superior nasal concha and receives the opening of the sphenoid sinus.

Drainage Pathway

1. Mucus is transported toward the sphenoidal ostium by ciliary activity.
2. Secretions pass through the natural sphenoidal ostium.
3. They enter the sphenoethmoidal recess.
4. Secretions then enter the posterior nasal cavity.
5. Mucociliary transport carries the material toward the nasopharynx.

Relationship to the Superior Nasal Concha

The superior nasal concha lies anterior and inferior to the sphenoethmoidal recess.

It is an important anatomical landmark for identifying the region containing the sphenoidal sinus opening.

Relationship to the Superior Nasal Meatus

The sphenoid sinus does not normally drain into the superior nasal meatus.

The superior meatus receives the posterior ethmoidal air cells, while the sphenoid sinus opens separately into the sphenoethmoidal recess above the superior nasal concha.

Relationship to the Ethmoidal Air Cells

The posterior ethmoidal air cells lie anterior to the sphenoid sinus.

The boundary between posterior ethmoidal and sphenoidal pneumatization varies considerably among individuals.

Onodi Cells

An Onodi cell is a posterior ethmoidal air cell that extends posteriorly and often superiorly in close relationship to the sphenoid sinus.

It may have an intimate relationship with the optic nerve, making recognition of this variation important in posterior ethmoidal and sphenoidal anatomy.

Mucosal Lining

The sphenoid sinus is lined by respiratory mucosa continuous with that of the nasal cavity.

The mucosa is relatively thin and contains ciliated respiratory epithelium responsible for transporting secretions toward the natural ostium.

Respiratory Epithelium

The lining consists predominantly of ciliated pseudostratified columnar epithelium with mucus-producing cells.

The coordinated movement of cilia helps maintain normal sinus clearance.

Mucociliary Clearance

Mucus within the sphenoid sinus is transported toward the sphenoidal ostium regardless of the effect of gravity alone.

Patency of the ostium and normal ciliary function are therefore important for sinus ventilation and drainage.

Functions

The sphenoid sinuses participate in the general functions attributed to the paranasal sinus system.

These include mucus production and clearance, contribution to conditioning of inspired air, reduction of the mass of portions of the skull, and contribution to resonance characteristics of the upper airway.

Development

The sphenoid sinus develops through pneumatization of the sphenoid bone during childhood.

It begins as an extension from the posterior nasal and sphenoethmoidal region and enlarges progressively with growth.

Pneumatization

The degree and direction of sphenoid pneumatization vary markedly.

This variation determines the relationships of the sinus to the sella turcica, clivus, optic canals, internal carotid arteries, and other skull base structures.

Patterns of Pneumatization

Sphenoid sinus pneumatization is commonly described according to its relationship to the sella turcica.

Pattern	General Description
Conchal	Minimal pneumatization of the sphenoid body
Presellar	Pneumatization extends toward but not substantially beneath the sella
Sellar	Pneumatization extends beneath the sella turcica

Sellar Type

In the sellar pattern, the sinus extends posteriorly beneath the sella turcica.

This configuration creates a particularly close relationship between the sinus roof and the pituitary fossa.

Presellar Type

In the presellar pattern, pneumatization extends posteriorly toward the anterior margin of the sella without substantially extending beneath it.

The bony separation between the nasal route and pituitary region is therefore greater than in a extensively pneumatized sellar sinus.

Conchal Type

In the conchal pattern, the sphenoid body remains predominantly solid with relatively little sinus pneumatization.

This pattern alters the anatomical corridor between the nasal cavity and sellar region.

Lateral Pneumatization

Pneumatization may extend laterally into portions of the sphenoid bone.

Extensive lateral pneumatization can increase the exposure of bony prominences related to the optic nerve, internal carotid artery, and other skull base structures within the sinus cavity.

Septal Variation

The intersinus septum is frequently eccentric and may be accompanied by accessory septa.

Septal attachments can occur near prominences produced by adjacent neurovascular structures, making individual anatomy important in surgical orientation.

Blood Supply

The sphenoid sinus receives arterial supply from branches associated with the posterior nasal and orbital arterial systems.

Important contributions include branches of the sphenopalatine artery and posterior ethmoidal artery.

Sphenopalatine Artery

The sphenopalatine artery is a terminal branch of the maxillary artery.

Its posterior nasal branches contribute to the blood supply of the posterior nasal cavity and sphenoidal region.

Posterior Ethmoidal Artery

The posterior ethmoidal artery arises from the ophthalmic artery.

It contributes to the vascular supply of posterior ethmoidal and neighboring sphenoidal structures.

Venous Drainage

Venous drainage of the sphenoid sinus communicates with venous networks of the posterior nasal cavity and neighboring skull base region.

These vessels have anatomical relationships with the pterygoid, orbital, and intracranial venous systems.

Sensory Innervation

Sensory innervation of the sphenoid sinus is derived from branches associated with the trigeminal nerve.

Posterior ethmoidal branches of the ophthalmic division and orbital or posterior nasal branches associated with the maxillary division may contribute to sensory innervation of the sphenoidal region.

Posterior Ethmoidal Nerve

The posterior ethmoidal nerve is associated with the nasociliary nerve of the ophthalmic division of the trigeminal nerve.

It provides sensory fibers to posterior ethmoidal and sphenoidal regions.

Maxillary Division Contributions

Branches associated with the maxillary division of the trigeminal nerve reach the posterior nasal and sphenoidal region through pathways associated with the pterygopalatine fossa.

These fibers contribute to general sensation from portions of the sinus mucosa.

Autonomic Innervation

Autonomic fibers regulate secretion and vascular tone within the sinus mucosa.

Parasympathetic secretomotor and sympathetic vasomotor fibers reach the region through autonomic pathways associated with the pterygopalatine ganglion and neighboring neurovascular structures.

Sphenoid Sinusitis

Inflammation of the sphenoid sinus is termed sphenoid sinusitis.

Mucosal swelling can obstruct the sphenoidal ostium, reducing ventilation and interfering with mucociliary drainage.

Clinical Importance of Deep Location

The sphenoid sinus occupies a deep central position in the skull and is surrounded by several important structures.

Its anatomical relationships differ from those of more anterior paranasal sinuses because the pituitary gland, cavernous sinus, optic apparatus, and internal carotid arteries are located nearby.

Optic Complications

The optic nerve may be separated from the sphenoid sinus by only a thin bony wall in some individuals.

This close anatomical relationship is important when evaluating disease or performing procedures involving the posterior paranasal sinus region.

Cavernous Sinus Relationships

The cavernous sinuses lie lateral to the sphenoid body.

Their proximity is anatomically important because they contain the internal carotid artery and are associated with cranial nerves controlling ocular movement and facial sensation.

Transsphenoidal Approach

The relationship between the sphenoid sinus and pituitary gland provides a natural surgical corridor to the sellar region.

In a transsphenoidal approach, the sphenoid sinus can be approached through the nasal cavity to gain access to the sella turcica while avoiding a direct transcranial route.

Endoscopic Transsphenoidal Surgery

Endoscopic approaches use nasal and sphenoidal landmarks to reach the sellar region.

Important landmarks include the sphenoidal ostia, sphenoid rostrum, intersinus septum, sellar prominence, optic prominences, and carotid prominences when these are identifiable.

Relationship to the Pituitary Fossa

The degree of sphenoid pneumatization strongly influences the appearance of the sellar floor from within the sinus.

In a well-pneumatized sellar sinus, the bony floor of the pituitary fossa may form a recognizable prominence in the superior posterior sinus wall.

Imaging

Computed tomography demonstrates the bony anatomy of the sphenoid sinus, including pneumatization, septa, ostia, and relationships with the optic canals and carotid canals.

Magnetic resonance imaging provides complementary information about neighboring soft tissues, particularly the pituitary gland, cavernous sinus region, optic structures, and intracranial contents.

Nasal Endoscopy

The sphenoethmoidal recess and sphenoidal ostium can be approached endoscopically through the posterior nasal cavity.

The superior nasal concha is an important landmark for orientation to this region.

Anatomical Variations

The sphenoid sinus demonstrates extensive anatomical variation.

Variation may involve sinus size, pneumatization pattern, number and position of septa, location of the ostium, and relationships with the optic nerve and internal carotid artery.

Important Variations

• Conchal, presellar, or sellar pneumatization
• Asymmetric right and left sinuses
• Deviated intersinus septum
• Accessory septa
• Lateral recess pneumatization
• Prominence of the optic canal
• Prominence of the internal carotid artery
• Variable thickness of bone over neurovascular structures
• Close association with posterior ethmoidal Onodi cells

Comparison with Other Paranasal Sinuses

Sinus	Location	Principal Drainage Region
Frontal sinus	Frontal bone	Middle meatus through frontal recess
Ethmoidal air cells	Ethmoidal labyrinth	Middle or superior meatus depending on group
Maxillary sinus	Body of maxilla	Middle nasal meatus
Sphenoid sinus	Body of sphenoid	Sphenoethmoidal recess

Key Anatomical Relationships

• The sphenoid sinuses are located within the body of the sphenoid bone.
• They are the most posterior paranasal sinuses.
• Right and left sinuses are usually separated by an asymmetric intersinus septum.
• Each sphenoid sinus opens into the sphenoethmoidal recess.
• The sphenoethmoidal recess lies superior and posterior to the superior nasal concha.
• The pituitary gland lies superior to the sinus within the sella turcica.
• The cavernous sinuses lie laterally.
• The internal carotid arteries are closely related to the lateral sinus walls.
• The optic nerves have close superolateral relationships with the sinus.
• The posterior ethmoidal air cells lie anterior to the sphenoid sinus.
• Onodi cells may have close relationships with the optic nerve and sphenoidal region.
• The clivus lies posterior to the sinus.
• Sphenoid pneumatization varies considerably among individuals.
• The sinus provides an important surgical corridor to the pituitary gland and central skull base.

Clinical Importance

The sphenoid sinus is especially important because of its deep position within the central skull base and its close relationships with major structures. The pituitary gland lies superiorly, the cavernous sinuses and internal carotid arteries lie laterally, and the optic nerves and optic chiasm are closely related to its superior region.

The sinus drains anteriorly through the sphenoidal ostium into the sphenoethmoidal recess rather than into one of the three principal nasal meatuses. The superior nasal concha provides an important landmark for locating this drainage region.

Understanding the sphenoid sinus provides the anatomical foundation for studying posterior paranasal sinus drainage, sphenoethmoidal recess anatomy, pituitary and sellar relationships, optic and carotid relationships, sphenoid sinusitis, skull base imaging, and transsphenoidal surgery.