The Anatomy of the Sphenoid Bone

The sphenoid bone (wasp bone) is part of the base of the skull

In This Article
Table of Contents

An unpaired bone located in the cranium (or skull), the sphenoid bone, also known as the “wasp bone,” is located in the middle and towards 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 holds the eyeball, and helps make up the floor of the middle cranial fossa, the butterfly-shaped depression at the base of the skull that houses the temporal lobes of the cerebellum.

A central bone within the skull, it has a very complex shape, with a body and two sets of wings—the lesser and greater wings—as well as two pterygoid processes (protrusions that descend from where the wings meet the body).

Disorders or problems of the sphenoid bone can lead to a number of conditions, including sphenoid sinusitis (an infection of the sphenoid sinuses), fractures, or sphenoid wing dysplasia—a malformation or deficiency due to neurofibromatosis type 1.

Anatomy

Structure

The sphenoid bone has a butterfly-like structure, with four major components—body, lesser wings, greater wings, and pterygoid processes.

Body

The central portion that runs along the midline, the body of the sphenoid bone rests between the wings and forms several important structures. The front-facing portion helps make up the nasal cavity, while its sides contribute to the formation of the optic canal, a tunnel that allows the optic nerve and ophthalmic artery to pass through.

The body’s upper surface forms the sella turcica and hypophoseal fossa (a small depression that houses the pituitary gland), as well as the dorsum sellae (a depression which slopes back at the base of the skull).

The front boundary of the latter is completed by two anterior clinoid processes, two bony protrusions (one on each side), and the rear makes up two other eminences called the posterior clinoid processes. These deepen the sella turcica, and are attached to the tentorium cerebelli, a portion of the dura mater of the brain.   

Lesser Wings

Rising from the front of the body of the sphenoid bone and moving off to the sides, the two paired lesser wings are triangular in shape. Their lower borders help make up part of the orbits (which house the eyes), while the upper surface makes up a portion of the cranial cavity, which houses parts of the brain.

Greater Wings

Emerging behind the lesser wings and also running to the sides are the two greater wings, which are also triangular and run lateral to the body. Their sides make up the infratemporal surfaces, which are convex in shape, and move backward and to the sides. These form parts of the infratemporal fossa, gaps at the base of the skull that allow nerves and blood vessels to pass through.

The front portions of the greater wings help form the sidewalls of the orbit. Each wing contains two major openings, which allow important nerves and vessels to pass through—the foramen rotundum and the foramen ovale.

Significantly, the superior orbital fissure, a large gap which allows nerves associated with vision to pass through, is at the border of the body, and the lesser and greater wings.   

Pterygoid Processes

Essentially extensions of the body of the sphenoid bone, the pterygoid processes consist of two protrusions emerging from the back of the body and moving downward. These include two canals—the pterygoid and the palatovaginal canals, which allow nerves to pass through, and each has a hamulus, or a smaller hook-like projection.

Location

The sphenoid bone rests in the central portion of the skull along its midline, separating the frontal bone (the forehead bone) from the occipital bone, a trapezoidal bone that makes up the lower back of the skull.

In addition, this bone articulates with (connects to) with a number of other bones along its sides, including the parietal bone, ethmoid, zygomatic, temporal, palatine, and vomer bones to make up a space to house the brain and allow for nerves and other structures to pass to and from there.

Largely, the sphenoid bone represents the floor of the skull.  

Anatomical Variations

Given the complexity of this bone, it’s little wonder that there are a number of congenital variations in its anatomy. These can be divided into pneumatization (the presence of holes in the bones) and protrusion (extension of the bone), and include:

  • Pterygoid process pneumatization: In from 15.5% to 43% of cases, doctors have found pneumatization—that is the presence of small holes—in the pterygoid process. This can occur on one side (unilaterally) or on both (bilaterally).
  • Anterior clinoid process pneumatization: The formation of holes has also been observed in the anterior clinoid process, which is towards the back of the body of the sphenoid bone. As with the pterygoid process, this is seen either unilaterally or bilaterally, and has been found to occur in about 13% to 16% of people.
  • Foramen rotundum protrusion: Extensions of extraneous bone into the foramen rotundum have been reported in approximately 17.5% of cases. As with some other variations, this can occur unilaterally or bilaterally.
  • Internal carotid artery (ICA) protrusion: The ICA, a paired artery that runs up the sides of the neck and accesses the skull, has been observed to protrude into the sphenoid sinus and related areas. This has been reported in 12.75% of cases. 
  • Pterygoid canal protrusion: Some people will have small protrusions arising from the pterygoid processes into the pterygoid canal. This has been reported to occur in between 7.5% and 13% of cases.

Function

Working in concert with the orbital floor, the primary function of the sphenoid bone is to help form the base and sides of the skull. Portions of this bone also are components of the facial skeleton.

Its central position within this part of the body makes it essential for providing rigidity—thereby protecting brain and nerve structures—while its rear parts are also attachments sites for muscles involved with chewing and talking.

Notably, too, the foramina (gaps) and the fissures of the sphenoid bone allow passage of important nerves and vessels in and out of the skull. Furthermore, a cavity in its body forms a sinus (called a sphenoid sinus) that connects to the nasal cavity; this allows the skull to be lighter and improves resonance.

Associated Conditions

There are several conditions that can affect the sphenoid bone; given its significance, these can have significant complications. Associated conditions include:

Sphenoid Sinusitis

Infection of the sphenoid sinuses can become a serious problem, and this can lead to either acute or chronic sphenoid sinusitis. Usually occurring alongside infection in surrounding areas, this condition can lead to fever, post-nasal drip, and weakness.

Seeking out prompt treatment is essential as, if allowed to run its course, patients may develop severe issues, such as meningitis, brain abscess, and/or problems with cranial nerves.

Sphenoid Fractures

Fracture of the sphenoid bone, often occurring when the orbit or base of the skull are impacted. Given its function, this can lead to numerous dangerous complications, including damage to cranial nerves, eyes, as well as loss of color vision.

Battle sign (a bruise on the face that’s a sign of skull fracture), hemotympanum (blood in the middle ear), and/or cranial nerve palsy (decreased or complete loss of cranial nerve function) are all signs of this condition, which is considered a medical emergency.

Sphenoid Wing Dysplasia

In patients with a condition called neurofibromatosis type 1, characterized by discoloration of the skin as well as the development of tumors in the skin, brain, and other parts of the body, the sphenoid wings can become malformed due to improper cellular development. This can lead to a wide range of symptoms, eventually leading to blindness, if untreated.

It’s important to note that if you suspect you have any of these conditions—or if you believe you’ve fractured this bone—you need to seek out medical attention immediately.

Treatment

Given the severity of the above-mentioned conditions, treatment needs to be timely and efficient. Luckily, today doctors are better able than ever before to take on issues of the sphenoid bone.

In the case of sphenoid sinusitis, while some, more mild and acute cases may be treated with medication, surgery is often indicated. The primary approach is a procedure called endoscopic transnasal sphenoidotomy, which entails surgically accessing the sphenoid sinus, widening it, and then removing infected portions.

In the case of fractures of this bone, much depends on the severity of the case. While certain kinds of sinus fracture can be taken on more conservatively (basically prescribing medications to take on pain and inflammation and ensuring healing is done properly), sphenoid fractures will typically require surgery to repair the fracture. This is because of the presence of essential nerve and vessel structures in this area.

Sphenoid wing dysplasia due to neurofibromatosis type 1 will also require surgical treatment, especially given how severe this case can get. Surgery is rather complex and varies; however, a popular approach involves draining excess fluid to ease pressure, locating the area (or areas) of defect, and using a specialized titanium mesh, bone cement, or bone graft to reinforce and the problematic area.

As always, timely treatment is absolutely essential for success, so don’t hesitate to contact your doctor if you suspect you’re having a sphenoid bone issue. 

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sieroslawski A. Sphenoid bone. Kenhub. 2020. 

  2. Jamil R, Callahan A. Anatomy, sphenoid bone. StatPearls. Updated May 7, 2020. 

  3. Turkdogan F, Turkdogan K, Dogan M, Atalar M. Assessment of sphenoid sinus related anatomic variations with computed tomographyPan Afr. Med. J. 2017;27.

  4. Charakorn N, Snidvongs K. Chronic sphenoid rhinosinusitis: management challengeJ Asthma Allergy. 2016;Volume 9:199-205.

  5. Ye L, Knipe H. Paranasal sinus fractures. Published 2020. 

  6. Concezio D, Amir S, Gianpiero T, Luca M, Mario G. Sphenoid dysplasia in neurofibromatosis type 1: a new technique for repairChilds Nerv Syst. 2017;33(6):983-986.