The optic canal is a cylindrical canal running obliquely through the lesser wing of sphenoid bone near the base where it joins the body of sphenoid. It transmits the optic nerve and ophthalmic artery (and its associated sympathetic fibers). The optic canal opens into the skull base at the optic foramen.
The ophthalmic artery lies inferior and lateral to the optic nerve within the optic canal.
See also
- optic canal enlargement
- optic nerve enlargement
- 1. Vogl TJ. Differential Diagnosis in Head and Neck Imaging. Thieme. (1999) ISBN:0865778116. Read it at Google Books - Find it at Amazon
- 2. Gray, H. and Carter, H. (2010). Gray's Anatomy. London: Arcturus.
The sphenoid bone is one of the eight bones that make up the cranium - the superior aspect of the skull that encloses and protects the brain.
Its name is derived from the Greek ‘sphenoeides’, to mean wedge-shaped.
In this article, we shall look at the anatomy of the sphenoid bone - its location, structure, and clinical significance.
[caption id="attachment_15976" align="aligncenter" width="763"]
Anatomical Structure
The sphenoid bone is said to be 'butterfly-shaped'. It consists of a body, paired greater wings and lesser wings, and two pterygoid processes.
Body
The body lies at the centre of the sphenoid bone, and is almost completely cubical in shape.
It contains the sphenoidal sinuses, which are separated by a septum - meaning that the sphenoid body is essentially hollow. The body articulates with the ethmoid bone anteriorly, and it is here that the sinuses open up into the nasal cavity.
The superior surface of the sphenoid body contains some important bony landmarks:
- Sella turcica - a saddle-shaped depression. It has three parts:
- Tuberculum sellae - forms the anterior wall of the sella turcica, and the posterior aspect of the chiasmatic groove.
- Hypophyseal fossa - the deepest part of the sella turcica, where the pituitary gland is located.
- Dorsum sellae - forms the posterior wall of the sella turcica.
- Chiasmatic groove - a sulcus formed by the optic chiasm (where the optic nerves partially cross).
The sella turcica is surrounded by the anterior and posterior clinoid processes. The anterior clinoid processes arise from the sphenoidal lesser wings, while the posterior clinoid processes are the superolateral projections of the dorsum sellae. They serve as attachment points for the tentorium cerebelli, a membranous sheet that divides the brain.
[caption id="attachment_15982" align="aligncenter" width="818"]
[caption id="attachment_9893" align="aligncenter" width="491"]
Greater Wing
The greater wing extends from the sphenoid body in a lateral, superior and posterior direction. It contributes to three parts of the facial skeleton:
- Floor of the middle cranial fossa
- Lateral wall of the skull
- Posterolateral wall of the orbit
There are three foramina present in the greater wing - the foramen rotundum, foramen ovale and foramen spinosum. They conduct the maxillary nerve, mandibular nerve and middle meningeal vessels respectively.
Lesser Wing
The lesser wing arises from the anterior aspect of the sphenoid body in a superolateral direction. It separates the anterior cranial fossa from the middle cranial fossa.
It also forms the lateral border of the optic canal - through which the optic nerve and ophthalmic artery travel to reach the eye. The medial border of the optic canal is formed by the body of the sphenoid.
There is a 'slit-like' gap between the lesser and greater wings of the sphenoid - the superior orbital fissure. Numerous structures pass through here to reach the bony orbit.
Pterygoid Process
The pterygoid process descends inferiorly from the point of junction between the sphenoid body and the greater wing. It consists of two parts:
- Medial pterygoid plate - supports the posterior opening of the nasal cavity.
- Lateral pterygoid plate - site of origin of the medial and lateral pterygoid muscles
Muscular Attachments
The lateral and medial pterygoid muscles which form some of the muscles of mastication originate from the lateral pterygoid plate of the sphenoid bone.
Articulations
The sphenoid is an unpaired bone. It sits anteriorly in the cranium, and contributes to the middle cranial fossa, the lateral wall of the skull, and the floor and sides of both orbits.
It has articulations with twelve other bones:
- Unpaired bones – Occipital, vomer, ethmoid and frontal bones.
- Paired bones – Temporal, parietal, zygomatic and palatine bones.
[start-clinical]
Clinical Significance - Transsphenoidal Surgery
The sphenoid bone shares a close anatomical relationship with the pituitary gland. Indeed, the pituitary can be accessed surgically by passing instruments through the sphenoid bone and sinus.
This type of surgery is known as endoscopic trans-sphenoidal surgery (ETSS), and is the usual treatment of choice for pituitary adenomas. It allows for the surgical management of pituitary pathology without the need for a more extensive craniotomy.
[caption id="attachment_15999" align="aligncenter" width="427"]
[end-clinical]
The sphenoid bone forms part of the hind wall of the orbits (upper aspect of the greater sphenoid wings) as well as the outside wall of the cranium behind the orbit (lateral aspect of the greater wings). From: Primate Anatomy (Third Edition), 2007
Author: Roberto Grujičić MD
•
Reviewer: Dimitrios Mytilinaios MD, PhD
Last reviewed: July 07, 2022
Reading time: 6 minutes
The sphenoid bone is one of the most complex bones of the human body. Due to its shape, it is also referred to as the 'wasp bone'. It makes up most of the middle part of the base of the skull and contributes to the floor of the middle cranial fossa of the skull.
The soft tissue structures such are the cranial nerves and parts of the brain are associated with this bone and have intense relations to it. The main function of the sphenoid bone is to provide the foramina and canals for the passage of neurovascular structures to and from the cranium.
In this article you will find out all about the anatomy of the sphenoid bone, its parts, borders, and development.
| Structure | Body (median portion) Two greater wings (lateral portion) Two lesser wings (anterior portion) Pterygoid processes (directed inferiorly) |
| Borders | Sphenofrontal suture - with the frontal bone Sphenoparietal suture - with the parietal bone Sphenosquamosal suture - with the temporal bone Spheno-ocipital suture - with the occipital bone (disappears by the age 25 and the bones fuse together) |
| Relations | Body: Anteriorly contributes to the nasal cavity; laterally - optic canal; superiorly - sella turcica, the hypophyseal fossa, dorsum sellae Lesser wings: Superolaterally - optic canal; inferiorly - lateral margin of the orbit; superiorly - cranial cavity; Together with the body and greater wings builds the superior orbital fissure (superior ophthalmic vein; ophthalmic, abducent, oculomotor and trochlear nerves) Greater wings: Anteriorly - posterior aspect of the lateral orbital wall; contain foramen ovale (madibular nerve, accessory meningeal artery, lesser petrosal nerve, emissary vein) and foramen spinosum (middle meningeal vessels, meningeal branch of the mandibular nerve) Pterygoid processes: contain pterygoid canal (major and deep petrosal nerves) and palatovaginal canal (pharyngeal nerve) |
The sphenoid bone has a common border with the frontal bone (via the sphenofrontal suture), the parietal bone (via the the sphenoparietal suture), the squamous part of the temporal bone (via the sphenosquamosal suture) and the occipital bone (via the spheno-occipital suture). As the sphenoid and occipital bone fuse during puberty ('tribasilar bone') the spheno-occipital suture disappears by the age of 25.
There are four main parts to the sphenoid bone including:
- The body of the sphenoid bone;
- The lesser wings;
- The greater wings;
- The pterygoid processes.
The body is the centrally positioned portion. Anteriorly, it contributes to the nasal cavity, laterally it builds the medial wall of the optic canal. Superiorly the body forms the sella turcica, the hypophyseal fossa and the dorsum sellae.
The sphenoidal sinuses are located in the sphenoid body behind the nasal cavity and divided by a septum. They contain the anterior and posterior clinoid processes respectively. The clivus slopes posterior to the body.
The lesser wings arise superolaterally from the sphenoid body where they form the optic canal which contains the optic nerve, ophthalmic artery. The inferior surface participates in the lateral margin of the orbit while the superior surface forms part of the cranial cavity.
The greater wings arise posterolaterally from the body of the sphenoid bone.
Their lateral surfaces form the infratemporal surfaces. Their anterior surfaces make up part of the posterior aspect of the lateral wall of the orbit.
They contain two important openings near their roots:
Between the body, lesser and greater wings is a large opening known as the superior orbital fissure where numerous nerves and vessels pass through. These vessels include the superior ophthalmic vein, ophthalmic nerve and its branches, abducent nerve, oculomotor nerve, trochlear nerve).
Ready to test yourself? Check out our skull bones quizzes and free diagrams.
The pterygoid processes are extensions of the basal surface of the sphenoid body. Each process consists of a medial pterygoid plate and a lateral pterygoid plate. The lateral plate is wider and shorter than the medial and serves as the origin of the medial and lateral pterygoid muscles. At the inferior tip of the medial pterygoid plate is the small hook-shaped process, the pterygoid hamulus.
The processes contain two canals known as the pterygoid canal and palatovaginal canal. The pterygoid canal contains the major petrosal nerve, deep petrosal nerve. The palatovaginal (or pharyngeal) canal contains the pharyngeal nerve.
The body and lesser wings of the sphenoid bone mature through classic endochondral ossification, whereas the pterygoid processes undergo intramembranous ossification.
The development of the greater wings of the sphenoid bone are exceptional since they are the only bony structures of the skull which go through both endochondral and intramembranous ossification.
All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.
References:
- Neil S. Norton, Frank H. Netter: Netter’s Head and Neck Anatomy for Dentistry, 2nd edition, Elsevier Saunders, p. 34, 49, 50, 55.
- M. Schünke, E. Schulte, U. Schumacher: Prometheus - Kopf, Hals und Neuroanatomie, 2nd edition, Thieme (2009), p.34-35
- Friedrich Anderhuber, Franz Pera, Johannes Streicher: Waldeyer Anatomie des Menschen, 19th edition, De Gruyter (2012), p.715-719
Illustrators:
- Pterygoid processes of sphenoid bone (ventral view) - Samantha Zimmerman
- Sphenoid bone (sagittal section) - Yousun Koh
Sphenoid bone: want to learn more about it?
Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.
What do you prefer to learn with?
“I would honestly say that Kenhub cut my study time in half.” – Read more.