SPHENOID: ANATOMY, PTERYGOID PROCESS, FUNCTIONS, INJURIES - ANATOMY AND PHYSIOLOGY - 2024

The sphenoid is an odd bone in the skull that is part of the facial skeleton. It is located in the middle part of the skull, behind the frontal bone and the ethmoid and in front of the occiput. It is one of the seven bones that articulate to form the orbit.

It is shaped like a butterfly or bat, since it has a central body with lateral wings. In its structure it has multiple orifices and channels through which neurological and vascular structures open.

Location of the sphenoid bone. By Images are generated by Japan Life Science Databases (LSDB). - from Anatomography, website maintained by Life Science Databases (LSDB). You can get this image through URL below. 次 の ア ド レ ス か ら こ の 画像 を 取得 で き ま す 。URL, CC BY-SA 2.1 jp, https: //commons.wikimedia.org / w / index.php? curid = 7743063

In its lower portion it has a projection on each side called the pterygoid process, which serves as an insertion surface for several of the muscles of the face. Multiple neurological elements run through this process.

The body of the sphenoid is hollow and forms the so-called sphenoid sinus, one of the eight paranasal sinuses. These air cavities of the bones are structures that influence phonation, in regulating the temperature of the air that enters through the nose and as a defense in infectious processes, among other functions.

Due to the relationships of the sphenoid with important nerves and arteries of the face and skull, its injuries involve serious sequelae for the patient, so they must be treated in a timely manner.

Embryology

Sphenoid began his training from 8 ^goes week of gestation in a complex process in which your body is first formed with the recess for the pituitary gland and subsequently its wings. By that time, these elements are separate.

Towards 9 ^to week they begin to form cartilage ossification nuclei that will eventually join into a single bone structure.

The sphenoid sinus, which is the hollow portion of the body, is formed from 12 ^to week when a cartilaginous portion invades the back bone and form a cavity filled with air years after birth.

The origin of the sphenoid is parallel to that of the brain, so it can be associated with some rare birth defects, such as transsphenoidal encephalocele, which is the exit of part of the brain through the body cavity of the sphenoid, due to abnormalities in its formation.

Anatomy

The sphenoid bone is one of the 22 bones that make up the skull and one of the 8 that make up the orbit. It represents the boundary between the neurocranium and the facial skeleton, joining both structures.

It is a large and complex bone that occupies the middle part, below the base of the skull. In front it borders the frontal bone and the ethmoid bone, and behind it the occipital bone. Its anterior limits allow stability to the skull and make an adequate and strong cavity for the brain.

Anterior and posterior view of the sphenoid. By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, It is made up of a cuboid body and lateral structures called sphenoid wings, in which two portions are recognized: major and minor.

In the body of the sphenoid a depression called the sella turcica is recognized, it is there where the pituitary gland is located. This body is hollow and forms one of the eight paranasal sinuses, the so-called sphenoid sinus.

Turkish chair By National Endocrine and Metabolic Diseases Information Service, NIH. - http://endocrine.niddk.nih.gov/pubs/prolact/prolact.htm, Public Domain, The sphenoid has multiple orifices and passage channels through which important vascular and neurological structures run. There are the optic canal, for the optic nerve, the foramen ovale, the superior orbital fissure and the spinous foramen.

In the position it occupies, it is articulated with 12 bones. Unique four: vomer, ethmoid, frontal and occipital; and 6 pairs: temporal, zygomatic, parietal and palatal.

Pterygoid process

The pterygoid process is a protrusion of the sphenoid that is located on each side of the point where the body meets the greater wing.

It is pyramidal in shape with a lower vertex and upper base. Two blades are described in its structure, one lateral and one medial.

Pterygoid process outlined in red (below). By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See «Book» section below) Bartleby.com: Gray's Anatomy, Plate 146, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 566521

The medial one has a horseshoe shape, its inner edge serves as an insertion surface for the tendon of the tensor palati muscle, while its outer edge constitutes part of the lateral limit of the choanas, which are the inner openings of the nasal cavity.

For its part, the lateral pterygoid and median pterygoid muscles are inserted in the lateral lamina. Together with the temporal bone, it contributes to the formation of some orifices for the passage of neurological structures.

Features

The sphenoid bone is essential at the junction of the facial and cranial bones. Its relationship and articulation with the rest of the bone structures, gives rigidity to the skull.

It also serves as an insertion surface for various muscles, especially the pterygoid process, where the chewing muscles insert.

It acts as protection for the important vascular and neurological structures that have passage between the brain, the facial space and the cervical.

The sphenoid sinus, like the rest of the paranasal sinuses, helps to reduce the weight of the skull, to drain nasal secretions, to warm the air that enters through the nose, to protect against respiratory infections and to improve resonance during phonation.

Injuries

Sphenoid fractures

Sphenoid fractures are complex and serious injuries that must be diagnosed and treated in a timely manner.

Partial or complete loss of vision is a common complication of injuries to the orbital portion of the bone. Thus, there may be multiple neurological sequelae depending on the degree of the injury, due to the multiple nerves that cross the bone.

The appearance of some signs such as that of Battle, which is the hematoma in the cutaneous projection of the mastoid process, may indicate injury to the sphenoid bone.

Whenever a skull base fracture with cranial nerve dysfunction is suspected, the possibility of injury to the sphenoid bone should be investigated.

Pterygoid process fractures

The pterygoid process fracture falls into the group of midface fractures called LeFort fractures.

Any facial fracture that involves severe trauma to the nose or frontal bone may involve the pterygoid process and the sphenoid bone.

LeFort fracture, indicated with an arrow. By James Heilman, MD - Own work, CC BY-SA 3.0, They are diagnosed from the history and physical examination. In turn, confirmation is made by imaging studies such as plain skull radiography and computerized axial tomography (CT).

The treatment of these fractures is surgical, since it is a life-threatening injury that affects the stability of the skull.

References

1. Jamil, R. T; Waheed, A; Callahan, AL (2019). Anatomy, Sphenoid Bone. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
2. Shumway, C.L.; Motlagh, M; Wade, M. (2019). Anatomy, Head and Neck, Orbit Bones. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
3. Liem, T., Becker, AR, & Panizo, A. (2002). Craniosacral osteopathy. Barcelona. Editorial Paidotribo
4. Koenen, L; Waseem, M. (2019). Orbital Floor (Blowout) Fracture. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
5. Cope, VZ (1917). The Internal Structure of the Sphenoidal Sinus. Journal of anatomy. Taken from: ncbi.nlm.nih.gov
6. Cappello, Z. J; Dublin, AB (2018). Anatomy, Head and Neck, Nose Paranasal Sinuses. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov