Sphenoid bone: anatomy, function and treatment

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The unpaired bone located in the skull (or skull), the sphenoid bone, also known as the wasp bone, is located in the middle and closer to the front of the skull, just in front of the occipital bone .

The sphenoid bone is one of the seven bones that make up the orbit (the space that houses the eyeball) and helps form the floor of the middle fossa, a butterfly-shaped depression at the base of the skull that houses the temporal bone. lobes of the cerebellum .

The central bone in the skull has a very complex shape with a body and two pairs of wings: one small and one large, as well as two pterygoid processes (protrusions that descend from where the wings meet the body).

Diseases or problems of the sphenoid bone can lead to a number of problems, including sphenoid sinusitis (an infection of the sphenoid sinuses), sphenoid wing fractures or dysplasia, a malformation or deficiency caused by a condition called neurofibromatosis type 1 .

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Anatomy

Composition

The sphenoid bone has a butterfly-shaped structure with four main components: the body, the minor wings, the major wings, and the pterygoid processes .

Body

Located in the central part that runs along the midline, the body of the sphenoid bone lies between the wings and forms several important structures. The front helps shape the nasal cavity and the sides help shape the optic canal, the tunnel through which the optic nerve and ophthalmic artery pass.

The upper surface of the sphenoid bone forms the sella turcica, which consists of the pituitary fossa (a small depression in which the pituitary gland is located), the dorsum of the sella turcica (a depression that extends backward at the base of the skull ). and tuberculum sellae.

The Turkish saddle is surrounded by two anterior clinoid processes and two bony protrusions (one on each side), and on its posterior side there are two other eminences, called posterior clinoid processes. They deepen the sella turcica and adhere to the tentorium cerebellum, part of the dura of the brain.

Small wings

Two small triangular-shaped paired wings rise from the front of the body of the sphenoid bone and extend to the sides. Its lower limits are part of the orbits (in which the eyes are located) and the upper surface is part of the cranial cavity, which contains parts of the brain.

Big wings

Behind the smaller wings, two large wings appear, which are also triangular in shape and run to the side of the body. Its sides form the infratemporal surfaces, which are convex and move back and forth. They form parts of the infratemporal fossa, which are grooves at the base of the skull through which nerves and blood vessels pass.

The anterior portions of the large wings help to form the lateral walls of the orbit. Each wing contains three openings: a circular opening, an oval opening, and a spiny opening through which important nerves and blood vessels pass. The maxillary nerve, the mandibular nerve, and the vessels of the meninges, respectively, pass through these openings.

Notably, the superior orbital fissure, the large space through which nerves associated with vision pass, is located at the edge of the body and the large and small wings.

Pterygoid processes

Continuing with the body of the sphenoid bone, the pterygoid processes consist of two protrusions that extend from the back of the body and continue downward. These include two canals, the pterygoid and the palatovaginal, through which nerves pass, each having a smaller, hooked protrusion or tubercle.

Location

The sphenoid bone is located in the central part of the skull along the midline, separating the frontal bone ( frontal bone) from the occipital bone, the trapezius that forms the lower part of the back of the skull.

In addition, this bone articulates (joins with) several other bones on the sides, including the parietal, ethmoid , zygomatic , temporal , palatine , and vomer bones, to form space for the brain and nerves. and other structures to get to and from there .

Basically, the sphenoid bone is the lower part of the skull.

Anatomical variations

Given the complexity of this bone, it should come as no surprise that there are a number of inherent variations in its anatomy. They can be divided into pneumatization (the presence of holes in the bones) and bulge (expansion of the bone), and these include the following.

  • Pterygoid process pneumatization : In 15.5-43% of cases, medical workers found pneumatization, that is, the presence of small holes in the pterygoid process. This can occur on one side (unilaterally) or on both sides (bilaterally).
  • Pneumatization of the anterior clinoid process : Hole formation was also observed in the anterior cuneiform process, which is closer to the posterior part of the body of the sphenoid bone. As with the pterygoid process, this occurs on the unilateral or bilateral side and has been found to occur in approximately 13 to 16% of people.
  • Bulging round hole : Foreign bone expansion in the circular foramen was reported in approximately 17.5% of cases. As with some other options, this can be done unilaterally or bilaterally.
  • Protrusion of the internal carotid artery (ICA) : The ICA, the paired artery that runs along the sides of the neck and leads to the skull, has been observed to protrude into the sphenoid sinus and associated areas. This was reported in 12.75% of the cases.
  • Pterygoid canal bulge : Sometimes small bumps arise from the pterygoid processes in the pterygoid canal. This is reported to occur between 7.5% and 13% of people.

Function

The main function of the sphenoid bone, which works in conjunction with the lower part of the orbit, is to form the base and sides of the skull. Parts of this bone are also components of the facial skeleton.

Its central position in this part of the body makes it important to provide rigidity, thus protecting the brain and nerve structures, while its backs are also points of attachment for the muscles involved in chewing and speaking.

It is also noteworthy that the foramina (clefts) and crevices of the sphenoid bone allow important nerves and vessels to enter and exit the skull. Also, a cavity in your body forms a sinus (called a sphenoid sinus), which connects to the nasal cavity; this allows the skull to be clearer and improves resonance.

Related conditions

There are several conditions that can affect the sphenoid bone; Given their importance, they can have serious complications. Associated terms include those listed below .

Wedge-shaped sinusitis

A sphenoid sinus infection can be a serious problem and can lead to acute and chronic sphenoid sinusitis. This disease is usually accompanied by infection in the surrounding areas and can lead to fever, postnasal discharge, and weakness.

Treatment should be sought immediately because if the infection progresses, patients can develop serious problems such as meningitis, brain abscess, and / or cranial nerve problems.

Sphenoid bone fractures

A sphenoid bone fracture affects the orbit or base of the skull. Given its function, this can lead to many dangerous complications, such as damage to the cranial nerves and eyes, and loss of color vision.

A battle mark (a bruise on the face that is a sign of a skull fracture), hemotympanum (blood in the middle ear), and / or cranial nerve palsy (decrease or complete loss of function of the cranial nerves) they are all signs of this condition. , which is considered a medical emergency.

Sphenoid wing dysplasia

In people with a condition called neurofibromatosis type 1 (characterized by discoloration of the skin and the development of tumors on the skin, brain, and other parts of the body), the wings of the sphenoid bone can become deformed due to improper cell development. This can lead to a wide range of symptoms that can ultimately lead to blindness if left untreated.

If you suspect that you have any of these conditions, or if you think the sphenoid bone has been broken, you should seek medical attention immediately.

Watch out

Given the severity of the above conditions, treatment must be timely and effective. Fortunately, healthcare professionals today are better able than ever to treat sphenoid bone problems.

For wedge-shaped sinusitis, although some milder and more severe cases can be treated with medication, surgery is often indicated. The main approach is a procedure called endoscopic transnasal sphenoidotomy, which involves surgically accessing the sphenoid sinus, expanding it, and then removing the infected portions.

In the case of a sphenoid bone fracture, much depends on the severity of the case. While certain types of sinus fractures can be treated more conservatively (essentially by prescribing medications to reduce pain and inflammation and ensure proper healing), sphenoid fractures generally require surgery to repair. This is due to the presence of important nervous and vascular structures in this area.

Wedge wing dysplasia caused by type 1 neurofibromatosis will also require surgical treatment, especially given the severity of the condition. The surgery is quite complex and varied; however, a popular method involves draining excess fluid to relieve pressure, identifying the defect area or areas, and using a special titanium mesh, bone cement, or bone graft to strengthen the problem area.

In these conditions, timely treatment is necessary for success. Don't hesitate to contact your doctor if you suspect you have a sphenoid bone problem.

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