The sphenoid bone is a single, unpaired bone nestled deep within the skull, centrally located just behind the eyes and beneath the front part of the brain. Often described as the “keystone” of the cranial structure, this complex bone provides structural integrity to the head. It connects and stabilizes numerous other bones, acting as a central brace for the entire cranium and facial skeleton.
Anatomical Position and Shape
The sphenoid bone occupies a strategic position at the intersection of the cranial vault and the facial skeleton. Lying in the middle of the skull base, it is situated anterior to the temporal bone and posterior to the frontal bone. Its intricate structure is often likened to a butterfly or a bat with extended wings.
This bone consists of a central body and three pairs of projections: the greater wings, the lesser wings, and the pterygoid processes. The greater wings sweep upward and outward, contributing to the side walls of the skull and the eye sockets. The smaller, shelf-like lesser wings form a portion of the roof of the orbital cavity.
The sphenoid bone articulates with almost all the other bones of the cranium. It connects directly with the frontal, temporal, parietal, occipital, and ethmoid bones, as well as facial bones like the vomer and palatine bones. This extensive set of connections highlights its role as a structural hub, linking the neurocranium (braincase) with the viscerocranium (face).
Critical Role in the Skull Base
The sphenoid bone forms the central, load-bearing platform of the middle cranial fossa, which is the floor of the skull. This positioning protects the delicate neurological and vascular structures that pass through the area. A prominent feature within the bone’s body is the sella turcica, Latin for “Turkish saddle.”
The sella turcica is a saddle-shaped depression that serves as the bony enclosure for the pituitary gland, a master endocrine gland. This recess provides protected housing for the gland, which regulates many of the body’s hormones. The sphenoid bone also contains a series of small, precisely located openings called foramina.
These foramina act as dedicated passageways for structures traveling between the brain and the rest of the head and face. The optic canal, for instance, allows the optic nerve to travel from the eye to the brain. Other openings, such as the foramen rotundum, foramen ovale, and superior orbital fissure, transmit cranial nerves and major blood vessels that supply the face and scalp.
Understanding the Sphenoid Sinus
The sphenoid sinuses are a pair of air-filled cavities within the body of the sphenoid bone, forming part of the paranasal sinus system. These cavities contribute to several physiological functions, including lightening the skull’s overall weight, which aids in balancing the head. The air spaces also influence voice quality, acting as resonating chambers.
The sinuses also play a role in respiration by helping to warm and humidify inhaled air before it reaches the lower respiratory tract. Like other sinuses, the sphenoid sinuses are lined with a mucous membrane that filters the air and traps foreign particles.
A common clinical issue is sphenoid sinusitis, which is inflammation or infection of the sinus lining. Because the sphenoid sinuses are located deep within the center of the skull, symptoms can be challenging to diagnose correctly. Patients often experience a deep-seated, persistent headache felt in the face, the vertex of the head, or the back of the skull (occipital region). This referred pain occurs due to the sinus’s proximity to various cranial nerves. Since the symptoms are vague and not always localized, the condition is sometimes misdiagnosed as migraine or tension headache.
The Transsphenoidal Surgical Approach
The deep, central location of the sphenoid bone and its sinus provides a unique pathway for a specialized surgical technique. The transsphenoidal approach is a minimally invasive method primarily used by neurosurgeons to access the pituitary gland and other structures near the skull base. This technique avoids the need for a traditional craniotomy, which involves opening the skull to reach the brain.
The procedure involves the surgeon passing instruments through the nasal cavity and navigating through the sphenoid sinus to reach the sella turcica. Because the sphenoid bone and sinus are directly in front of the pituitary gland, they offer the most direct and least disruptive route to the target area. The use of this natural cavity minimizes trauma to surrounding brain tissue.
This approach is favored because it generally results in less post-operative pain and a shorter recovery time compared to open-skull surgery. While complex, the transsphenoidal route is an effective way to remove pituitary tumors and treat other lesions in this sensitive region.