Bones - Sphenoid Bone

Question 1

Sphenoid body

Features?

Bony landmarks?

Answer 1

Sphenoidal sinuses - separated by a sinus - body articulates with the ethmoid anteriorly where the sinuses open up into the nasal cavity. The opening of the sphenoidal sinus can be found on the anterior surface of the body.

Sella turcica:

1) Anteriorly - tuberculum sellae (elevation posterior to optic chiasm)
2) Posteriorly - dorsum sellae (square-shaped)
3) Deep - hypophyseal fossa, where the pituitary gland is located.
4) Chiasmatic sulcus - anterior to the tuberculum sellae - a groove where the optic nerve passes.
5) Anterior and posterior clinoid processes - serve as attachment points for the tentorium cerebelli and the diaphragm sellae.

Question 2

Greater wing of sphenoid

Contributions to which part of the facial skeleton?

Foramina and their contents?

Answer 2

• Floor of the middle cranial fossa
• Posterolateral wall of the bony orbit
• Lateral wall of the skull

Foramina:

Foramen rotundum - inferior to the superior orbital fissure and superolateral to the pterygoid canal - conducts the maxillary nerve.

Foramen ovale - anteromedial to the foramen spinosum and posterolateral to the foramen rotundum - transmits the mandiular, lesser petrosal nerve, and the venous plexus of the foramen ovale.

Foramen spinosum - immediately posterolateral to the foramen ovale - transmits the middle meningeal artery, veins and the meningeal branch of the mandibular nerve.

Question 3

Lesser wing of Sphenoid

Orientation?

Contribution to the facial skeleton?

Which fossa does it separate?

Foramina?

Answer 3

Located anterior to the body of sphenoid and emerges in a superolateral direction.

Forms the posteromedial aspect of the bony orbit.

It separates the anterior cranial fossa from the middle cranial fossa.

1) Optic canal - Forms the lateral aspect of the optic canal - transmits the ophthalmic artery and nerve.
2) Superior orbital fissure - the lesser wing forms the superomedial aspect of the fissure - transmits various structures:
i) Occulomotor nerve (CN III)
ii) Trochlear nerve (CN IV)
iii) Abducens nerve (CN VI)
iv) Ophthalmic nerve (a branch of CN V) and its branches
v) Superior and inferior ophthalmic veins

Question 4

Pterygoid plates

Origin?

Fossae?

Answer 4

Originates from the junction between the body and greater wing.

1) Medial pterygoid plate - supports the posterior opening of the nasal cavity.
2) Lateral pterygoid plate - site of origin of the lateral and medial pterygoid muscles

Between the two plates is the pterygoid fossa.

Question 5

Clinical relevance: transsphenoidal surgery

Answer 5

The pituitary gland can be accessed by passing instruments through the sphenoid bone and sinus.

This type of surgery is a form of endoscopy and is the usual treatment choice for pituitary adenomas.