Understanding the Sphenoid Bone: Anatomy, Articulations, and Clinical Significance
Introduction
The sphenoid bone is one of the eight bones that make up the neurocranium. It is butterfly-shaped and an irregular, unpaired bone. It consists of a body and 3 pairs of processes:
- Greater wings
- Lesser wings
- Pterygoid processes
Anatomical Location
It is wedged between the frontal, temporal, and occipital bones. It sits anteriorly in the cranium. It contributes to:
- The anterior and middle cranial fossa
- The lateral wall of the skull
- The floor and sides of the orbits
- The infratemporal fossa
Articulations
It has articulations with 12 other bones:
Unpaired bones:
- Occipital
- Vomer
- Ethmoid
- Frontal bones
Paired bones:
- Temporal
- Parietal
- Zygomatic
- Palatine bones
The Body Of The Sphenoid
- Lies at the centre of the sphenoid bone
- It is almost completely cubical in shape
- It is a hollow bone – it contains sphenoidal sinuses which are separated by a septum. The sinuses open up into the nasal cavity by the anterior articulation of the body with the ethmoid bone.
- The superior surface of the sphenoid body contains some important bony landmarks:
Sella Turcica
It is a saddle-shaped depression. It has 3 parts:
- Tuberculum sellae (horn of saddle)
- It is a median elevation that forms the anterior wall of the sella turcica
- It is the posterior boundary of the prechiasmatic groove
- The anterior boundary of the hypophysial fossa
- Hypophysial fossa/pituitary fossa (seat of saddle)
- It is the deepest part of the sella turcica
- It accommodates the pituitary gland
- Dorsum sellae (back of saddle)
- A square plate of bone projecting superiorly from the body of the sphenoid
- It forms the posterior boundary of the sella turcica
- Its prominent superolateral angles make up the posterior clinoid process
It is surrounded by:
- The anterior clinoid process – arising from the lesser wing of sphenoid
- The posterior clinoid process – superolateral projections of the dorsum sellae
They serve as attachment points for the tentorium cerebelli (a membranous sheet that divides the brain)
Chiasmatic Groove
- A sulcus formed by the optic chiasm (where the optic nerves partially cross)
The Greater Wings
- They extend from the sphenoid body in a lateral, superior and posterior direction
- It has 4 surfaces:
- Cerebral surface – contributes to the floor of the middle cranial fossa
- Orbital surface – contributes to the posterior wall of the orbit
- Temporal surface – contributes to the lateral wall of the skull
- Infratemporal surface – contributes to the infratemporal fossa
There are 3 foramina present in the greater wings:
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Foramen rotundum
- It is located posterior to the medial end of the superior orbital fissure
- It opens into the pterygopalatine fossa
- It conducts the maxillary nerve
-
Foramen ovale
- It is located posterolateral to the foramen rotundum
- It opens into the infratemporal fossa
- It conducts the mandibular nerve
-
Foramen spinosum
- It is located posterolateral to the foramen ovale
- It opens into the infratemporal fossa (in relationship with the spine of the sphenoid)
- It conducts the middle meningeal vessels
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The superior orbital fissure is a slit-like gap between the lesser and greater wings of the sphenoid. It opens anteriorly into the orbit. Numerous structures pass through here to reach the bony point.
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These 3 foramina, along with the superior orbital fissure, from the crescent of four foramina
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[The foramen lacerum (not part of the crescent of foramina) is located between the sphenoid and temporal bones, posterolateral to the hypophysial fossa]
The Lesser Wings
- They arise from the anterior aspect of the sphenoid body in a superolateral direction
- Is separates the anterior cranial fossa from the middle cranial fossa
- It also forms the lateral border of the optic canal, through which the optic nerve and ophthalmic artery travel. The medial border of the optic canal is formed by the body of the sphenoid.
The Pterygoid Processes
- They extends inferiorly on each side from the junction of the body and greater wings
- It consists of 2 parts:
- Medial pterygoid plate – supports the posterior opening of the nasal cavity
- Lateral pterygoid plate – site of origin of the medial and lateral pterygoid muscles
Clinical Correlates
Endoscopic Trans-sphenoidal Surgery (ETSS)
- This is a type of surgery where the pituitary gland is accessed surgically by passing instruments through the sphenoid bone and sinus
- It is usually the treatment of choice for pituitary adenomas
- It allows for the surgical management of pituitary pathology without the need for a more extensive craniotomy
