Learning Objective: Describe the anatomy of the sphenoid bone, including its parts, articulations, foramina, muscular attachments, and clinical significance, such as transsphenoidal surgery.
The sphenoid bone is an unpaired, wedge-shaped (sphenoeides) bone located centrally in the skull. It contributes to the middle cranial fossa, the lateral walls of the skull, and the floor and sides of the orbits. Its ‘butterfly shape’ is formed by a central body, paired greater wings, paired lesser wings, and two pterygoid processes.
Anatomical Structure
Body
- Cuboidal, hollow, contains sphenoidal sinuses separated by a septum.
- Articulates anteriorly with the ethmoid bone; sinuses drain into the nasal cavity.
- Superior surface landmarks:
- Sella turcica: saddle-shaped depression for the pituitary gland
- Tuberculum sellae: anterior wall; posterior chiasmatic groove
- Hypophyseal fossa: the deepest part, houses the pituitary gland
- Dorsum sellae: posterior wall
- Chiasmatic groove: sulcus for optic chiasm
- Anterior and posterior clinoid processes: attachment for tentorium cerebelli
Greater Wing
- Extends laterally, superiorly, and posteriorly.
- Contributes to:
- Floor of the middle cranial fossa
- Lateral skull wall
- Posterolateral orbit wall
- Contains three foramina:
- Foramen rotundum: maxillary nerve (CN V2)
- Foramen ovale: mandibular nerve (CN V3)
- Foramen spinosum: middle meningeal vessels
Lesser Wing
- Arises anteriorly and superolaterally; it separates the anterior from the middle cranial fossa.
- Forms the lateral border of the optic canal (optic nerve and ophthalmic artery).
- The superior orbital fissure lies between the lesser and greater wings; it transmits cranial nerves III, IV, V1, VI, and ophthalmic veins.
Pterygoid Process
- Descends inferiorly from the junction of the body and the greater wing.
- Medial plate: supports the posterior nasal cavity
- Lateral plate: origin of the medial and lateral pterygoid muscles
Muscular Attachments
-
Lateral pterygoid plate: origin of medial and lateral pterygoid muscles (mastication)
Articulations
The sphenoid articulates with 12 bones:
- Unpaired: occipital, vomer, ethmoid, frontal
- Paired: temporal, parietal, zygomatic, palatine
Clinical Significance
Transsphenoidal Surgery (ETSS)
- The pituitary gland lies in close relation to the sella turcica.
- Endoscopic transsphenoidal surgery allows access through the sphenoid sinus to remove pituitary adenomas without craniotomy.
- Advantages: minimally invasive, reduced morbidity, direct midline access.
