Os sphenoidale – Sphenoid Bone: Anatomy & Function

What is the Os sphenoidale?

The Os sphenoidale, commonly known as the sphenoid bone, is an unpaired bone situated at the central base of the skull. Its distinctive butterfly- or bat-like shape – with a body, two greater wings, two lesser wings, and two pterygoid processes – makes it one of the most anatomically complex bones in the human body. The sphenoid bone is a key component of the cranium and articulates with numerous other skull bones.

Anatomy and Structure

The sphenoid bone is divided into several distinct parts:

• Body (Corpus sphenoidalis): The central portion that houses the sella turcica, a saddle-shaped depression that cradles the pituitary gland (hypophysis). Within the body lie the paired sphenoidal sinuses, which are part of the paranasal sinus system.
• Greater Wings (Alae majores): The large lateral extensions that form parts of the middle cranial fossa, the temporal region, and the lateral wall of the orbit.
• Lesser Wings (Alae minores): The smaller, superior projections that contribute to the anterior cranial fossa and the roof of the orbit. Between the lesser and greater wings lies the superior orbital fissure, through which important cranial nerves and vessels pass.
• Pterygoid Processes (Processus pterygoidei): Downward projections that serve as attachment points for muscles of mastication and form the pterygoid fossa.

Key Foramina and Canals

The sphenoid bone contains several important openings through which nerves and blood vessels pass:

• Optic canal (Canalis opticus): Transmits the optic nerve (CN II) and the ophthalmic artery.
• Foramen rotundum: Transmits the maxillary nerve (CN V2).
• Foramen ovale: Transmits the mandibular nerve (CN V3).
• Foramen spinosum: Transmits the middle meningeal artery.
• Superior orbital fissure: Transmits cranial nerves III, IV, V1, and VI, as well as ophthalmic veins.

Functions of the Sphenoid Bone

The sphenoid bone serves several critical functions:

• It forms a major portion of the skull base, contributing to the stability of the cranium.
• It protects the pituitary gland within the sella turcica from mechanical damage.
• Its sphenoidal sinuses help warm, humidify, and filter inhaled air.
• It serves as a conduit for important cranial nerves and blood vessels.
• It contributes to the formation of the orbit and the temporal fossa.

Clinical Relevance

Due to its central position and close relationship to vital anatomical structures, the sphenoid bone carries significant clinical importance.

Fractures

Sphenoid bone fractures typically result from severe head trauma. Because the sphenoid is closely associated with the internal carotid artery, the pituitary gland, and numerous cranial nerves, fractures can lead to serious complications such as cranial nerve palsies, vision loss, hormonal deficiencies (due to pituitary damage), or life-threatening hemorrhage.

Sphenoidal Sinusitis

Sphenoidal sinusitis – inflammation of the sphenoidal sinuses – is uncommon but potentially dangerous. Symptoms include diffuse headache (often in the occipital or vertex region), a sensation of pressure, and, if the infection spreads, a risk of meningitis or brain abscess formation.

Pituitary Tumors

Pituitary tumors such as pituitary adenomas are located in direct proximity to the sphenoid bone. They are frequently removed via a transsphenoidal approach – passing through the sphenoidal sinus – which is a minimally invasive surgical technique that takes advantage of the anatomical position of the Os sphenoidale as a natural surgical corridor.

Significance in Medical Imaging

In radiology, particularly in computed tomography (CT) and magnetic resonance imaging (MRI) of the skull, the sphenoid bone serves as an important anatomical landmark. Changes in this bone may indicate tumors, inflammatory disease, or traumatic injury.

Development and Ossification

The sphenoid bone develops from multiple ossification centers that fuse during embryonic development and early childhood. Complete ossification is generally achieved by the end of the first decade of life. The bone is formed by both endochondral ossification (from cartilage) and intramembranous ossification (from connective tissue).

References

1. Drake R.L., Vogl A.W., Mitchell A.W.M. – Gray's Anatomy for Students. Elsevier, 4th Edition, 2019.
2. Standring S. (Ed.) – Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier, 42nd Edition, 2020.
3. Moore K.L., Dalley A.F., Agur A.M.R. – Clinically Oriented Anatomy. Wolters Kluwer, 8th Edition, 2018.