sphenoids

Sphenoids is a rarely used plural term referring to the sphenoid bone of the skull. The sphenoid bone is a single, wedge-shaped bone located at the base of the skull, central between the eye sockets and the temporal bones. It forms part of the floor of the cranial cavity and the walls of the orbits, contributing to both the cranial base and the orbital apex.

The bone has several distinct parts: a central body, two wing groups (greater wings and lesser wings), and downward-projecting pterygoid processes. The body contains the sphenoidal sinuses in many individuals. The superior surface features the sella turcica, a saddle-shaped groove that houses the pituitary gland. The greater wings extend laterally and participate in the middle cranial fossa and the orbital walls, while the lesser wings form part of the anterior cranial fossa and help create the optic canal. The pterygoid processes provide attachment points for muscles of mastication and the soft palate.

Key openings and canals include the optic canal in the lesser wing (for the optic nerve and ophthalmic artery), the superior orbital fissure between the greater and lesser wings (for nerves and vessels passing to the orbit), and the foramina rotundum, ovale, and spinosum in the greater wing (transmitting branches of the trigeminal nerve and middle meningeal vessels). The orifices are complemented by the larger sphenoidal contributions to the foramen lacerum at the skull base.

Embryology and variation: the sphenoid develops from multiple ossification centers and fuses into a single bone during late fetal life or early infancy. Clinically, sphenoid fractures or lesions can affect the pituitary gland, cavernous sinus, optic nerve, or internal carotid arteries, and the bone is a common target for transsphenoidal surgical approaches.

Etymology: from Greek spheneidos, wedge-shaped.