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This is the free full text of AppSurgeOn - 3D Skull Atlas.

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Sphenoid Bone

The sphenoid bone is located in the middle of the skull base, between the frontal, ethmoidal, occipital, and temporal bones. It has a butterfly-like shape, with a central body, and greater and lesser wings spreading laterally from the body on both sides. In addition, it shows two inferiorly directed pterygoid processes arising at the junction between the body and the greater wings. The sphenoid bone contributes to the lateral and superior walls of the orbit, to the floor and lateral walls of the skull, to the roof of the rhinopharynx, and to the posterior wall of the nasal cavities. Moreover, it constitutes the posterior wall of the pterygopalatine fossa and the medial wall of the infratemporal fossa. The body of the sphenoid is pneumatized, containing the sphenoid sinuses. It articulates with the ethmoid, frontal, parietal, zygomatic, temporal, occipital, vomer, and palatine bones.

 

   

 

Parts

 

Body

It is roughly cuboid shaped and contains two sphenoid sinuses, separated by the intersinusal septum. Its superior surface constitutes the planum, or jugum, sphenoidale, which is bound posteriorly by the prechiasmatic sulcus. The optic canals are located lateral to the prechiasmatic sulcus, and the tuberculum sellae can be seen posterior to it. The variably prominent middle clinoid processes may be visible lateral to the tuberculum. The pituitary fossa is bound anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae, contributing to the formation of the sella turcica on the superior surface of the body. The pituitary fossa does not present lateral walls and it is in continuity with the carotid sulci and the superior surfaces of the greater wings, lateral to the sulci. The posterior clinoid processes are present on the superolateral part of the dorsum sellae, while the petrosal processes are located below the dorsum sellae. The lateral edge of each carotid sulcus is constituted of the lingula. The anterior surface of the body is marked by the sphenoidal crest, which is located between the sphenoidal conchae. The conchae are divided into anterior and posterior parts, and surround the ostia of the sphenoid sinuses. The inferior surface of the body presents the sphenoid rostrum, bound laterally by the progressively diverging edges of the sphenoidal crest. The thin vaginal processes are present medial to the pterygoid processes.

 

Greater wings

Two processes arising from the body and contributing to the skull base and the lateral wall of the skull. The triangular posterior edge of the wing wedges between the petrous and the squamous parts of the temporal bone, constitutes the anterior limit of the medial half of the foramen lacerum, and presents the posterior opening of the Vidian, or pterygoid, canal. The foramina ovale, rotundum, and spinosum are visible on the superior surface, piercing both of the greater wings. The foramina ovale and spinosum are seldom confluent. The sphenoid emissary foramen (of Vesalius) may be present medial to the foramen ovale in approximately 40% of people, and connect the cavernous sinus with the pterygoid venous plexus. The lateral surface of the greater wing is marked by the infratemporal crest, that reaches the anterior aspect of the lateral pterygoid plate.
The inferior surface is pierced by the foramina ovale and spinosum, while the foramen rotundum opens on the anterior surface below the medial end of the superior orbital fissure. The sphenoid spine projects inferiorly from behind the foramen spinosum, and is marked medially by the groove for the chorda tympani. The sulcus tubae is present near the sphenoid spine. Lateral to the sphenoid spine, the rough surface for the articulation with the squamous part of the temporal bone faces internally, while in the part of the greater wing contributing to the lateral wall of the skull it faces externally. The superior edge of the greater wing has a rough triangular area on the internal surface for the articulation with the frontal bone, which continues medially as the inferior margin of the superior orbital fissure. Its anterior angle and the anterior edge of the greater wing articulate with the zygomatic bone. The orbital surface is located between the anterior edge of the greater wing and the inferior margin of the superior orbital fissure. The foramen of Hyrtl piercing the orbital surface may be observed. The inferior border of the orbital surface bounds the inferior orbital fissure posterolaterally.

The internal surface of the greater wing is grooved by the impression of the frontal branch of the middle meningeal artery.

 

Lesser wings

Two triangular bone projections arising from the body and directed laterally. They separate the anterior and the middle cranial fossae, projecting posteriorly towards the lateral fissures of the cerebral hemispheres. The posterior edge of the lesser wing continues medially into the anterior clinoid process, which may join the middle clinoid process to form the carotico-clinoid foramen. The anterior clinoid process shows also two insertions on the body of the sphenoid: a superior thin root, above the optic canal; and an inferior thick root, namely the optic strut, found below the optic canal.

 

Pterygoid processes

They arise from the junction between the greater wings and the body of the sphenoid, and direct inferiorly. Each process shows the medial and the lateral pterygoid plates, which are separated by the pterygoid fossa. The superior parts of the medial and the lateral plates are fused anteriorly, while their inferior parts diverge, constituting the pterygoid fissure. The posterior edge of the medial plate presents the processus tubarius at its midpoint, the pterygoid tubercle at its upper end, and the pterygoid hamulus at its lower end. The medial plate splits superiorly to enclose the scaphoid fossa. The vaginal process is located medial to the medial pterygoid plate, and contributes to the palatovaginal canal, articulating with the sphenoidal process of the palatine bone. It further articulates with the ala of the vomer, contributing to the vomerovaginal canal. The anterior surface of the root of the pterygoid process is pierced by the anterior opening of the Vidian, or pterygoid, canal.

  

Sphenoidal conchae

Curved plates arising from the inferior part of the anterior aspect of the body of the sphenoid. Each of them has an anterior vertical part completing the posterior ethmoidal sinuses, and a posterior horizontal part constituting part of the nasal roof. They are pierced by the ostium of the sphenoid sinus. The sphenoidal crest and the sphenoid rostrum are located between the conchae. The posterosuperior surface of the concha contributes to the formation of the walls of the sphenoid sinus.

 

Superior orbital fissure

The opening connecting the cranial cavity and the orbit. It is bound medially by the body of the sphenoid, superiorly by the lesser wing, inferiorly by the greater wing, and laterally by the frontal bone between the greater and the lesser wings.

 

Articulations

The sphenoid bone articulates with the ethmoid, frontal, parietal, zygomatic, temporal, occipital, vomer, and palatine bones.

Anatomical Details

Anterior Clinoid Process

The posteriorly directed, medial prolongation of the posterior edge of the lesser wing. The anterior and middle clinoid processes are sometimes united to form a carotico-clinoid foramen.

 

Carotid Sulcus

The sulcus located above the root of the greater wing accommodating the internal carotid artery.

 

Chorda Tympani Groove

A groove on the medial side of the spine of the sphenoid. It houses the chords tympani nerve after its exit from the petro-tympanic fissure.

 

Dorsum Sellae

Approximately rectangular-shaped process posterior to the pituitary fossa. It constitutes the upper 1/3 of the clivus. The remaining 2/3 are formed by the portion of sphenoid bone posteroinferior to the dorsum sellae and by the basilar portion of the occipital bone.

 

Foramen Ovale

The foramen located anteromedial to the foramen spinosum, posterolateral to the foramen rotundum, and lateral to the foramen lacerum. It connects the middle cranial fossa and the infratemporal fossa, transmitting the mandibular nerve, the lesser petrosal nerve, the venous anastomosis between the cavernous sinus and the pterygoid venous plexus, and the accessory meningeal branch, arising from the maxillary artery. Occasionally the foramen ovale is fused with the foramen spinosum.

 

Foramen Rotundum

The most anteromedial of the three foramina of the greater wing of the sphenoid bone. It connects the middle cranial fossa and the pterygopalatine fossa, transmitting the maxillary nerve.

 

Foramen Spinosum

The smaller and rounder foramen of the greater wing of the sphenoid. It is located posterolateral to the foramen ovale, transmitting the middle meningeal artery and a recurrent meningeal branch of the mandibular nerve. Occasionally the foramen ovale is fused with the foramen spinosum, or the posterior edge of the foramen spinosum can be absent.

 

Greater Wing

Process arising from the body of the sphenoid and extending posterolaterally from the skull base to the lateral surface of the skull. Its concave internal surface is part of the middle cranial fossa. Its triangular posterior edge is located in the angle between the petrous and squamous parts of the temporal bone. Its posterior edge is the anterior limit of the medial half of the foramen lacerum.

 

Hyrtl Foramen

A foramen that can be present on the greater wing, connecting the middle cranial fossa and the orbit. It is lateral to the superior orbital fissure, below the posterior margin of the lesser wings of the sphenoid bone. It houses the meningolacrimal artery, when present, or occasionally a recurrent meningeal branch from the lacrimal artery.

 

Infratemporal Crest

Ridge that divides the lateral surface of the greater wing into temporal and infratemporal surfaces. It continues anteromedially and inferiorly towards the anterior aspect of the lateral pterygoid plate, bounding the pterygo-maxillary fissure posteriorly.

 

Lateral Pterygoid Plate

Broad and thin plate showing a slight lateral concavity and projecting posterolaterally. Its lateral surface, which forms part of the medial wall of the infratemporal fossa, gives origin to the lateral pterygoid muscle. Its medial surface forms the lateral wall of the pterygoid fossa. The upper part of its anterior border is the posterior boundary of the pterygo-maxillary fissure, while its lower part articulates with the palatine bone.

 

Lesser Wing

A triangular process arising laterally from the anterosuperior region of the body. Its separates the frontal lobe of the brain from the superior orbital fissure and the temporal lobe. Its posterior edge separates the anterior and the middle cranial fossae.

 

Lingula

The bony crest arising as the lateral edge of the carotid sulcus, and extending posteriorly over the posterior opening of the pterygoid canal.

 

Medial Pterygoid Plate

Narrower and longer plate with respect to the lateral one, with a sharp posterior edge. Its lateral surface forms the medial wall of the pterygoid fossa; while its medial surface is the lateral boundary of the posterior nasal aperture. It articulates with the posterior border of the perpendicular plate of the palatine bone in the lower part of its anterior margin. The posterior margin of the medial pterygoid plate gives insertion to the pharyngobasilar fascia. The lower end of the medial pterygoid plate gives attachment to the superior pharyngeal constrictor.

 

Middle Clinoid Process

Variably prominent process inferolateral to the tuberculum sellae and medial to the carotid sulcus. The anterior and middle clinoid processes are sometimes united to form a caroticoclinoid foramen.

 

Middle Meningeal Frontal Branch Groove

The impression of the frontal branch of the middle meningeal artery on the internal surface.

 

Optic Canal

The canal connecting the cranial cavity and the orbit containing the optic nerve and the ophthalmic artery.

 

Optic Strut

The thick triangular root posteroinferior to the optic canal. It corresponds to the lateral optico-carotid recess visible from inside the sphenoid sinus.

 

Palatovaginal Canal

The groove on the inferior surface of the vaginal process that is completed anteriorly by the sphenoidal process of the palatine bone to form the palatovaginal canal. The palatovaginal canal transmits the pharyngeal branches from the maxillary artery and the pterygopalatine ganglion.

 

Petrosal Process

The small process present below the dorsum sellae articulating with the apex of the petrous part of the temporal bone.

 

Pituitary Fossa

The fossa, contained in the sella turcica, housing the pituitary gland. It is bounded by bony walls only anteriorly and posteriorly.

 

Planum Sphenoidale

The smooth part located anteriorly on the superior surface, between the lesser wings and anterior to the prechiasmatic sulcus. Synonym: Jugum sphenoidale.

 

Posterior Clinoid Process

The process arising from the superior lateral angle of the dorsum sellae. It gives insertion to the diaphragma sellae and the tentorium cerebelli.

 

Prechiasmatic Sulcus

The sulcus extending between the optic canals and lying anterior to the tuberculum sellae. It constitutes the posterior border of the planum.

 

Processus Tubarius

The process located in the midpoint of the posterior edge of the medial pterygoid plate. It is attached to the pharyngeal end of the pharyngo-tympanic tube.

 

Pterygoid Fossa

The cuneiform fossa between the medial and the lateral pterygoid plates. The upper parts of the pterygoid plates are fused closing the fossa anteriorly. Their inferior parts are separated delineating the pterygoid fissure, which is closed anteriorly by the pyramidal process of the palatine bone. Medial pterygoid and tensor veli palatini muscles originate from the pterygoid fossa.

 

Pterygoid Hamulus

The unciform, laterally directed process arising from the inferior end of the medial pterygoid plate. It gives attachment to the pterygo-mandibular raphe, and the tendon of tensor veli palatini curves medially around it.

 

Pterygoid Tubercle

The small tubercle inferior to the posterior opening of the Vidian canal, at the upper end of the medial pterygoid plate.

 

Scaphoid Fossa

The fossa comprised between the two laminae created by the subdivision of the medial pterygoid plate in its superior portion. It gives origin to part of the tensor veli palatini muscle.

 

Sella Turcica

The superior part of the body of the sphenoid, above the sphenoid sinus, containing the pituitary gland into the pituitary fossa.

 

Sphenoidal Concha Anterior Part

Vertical quadrangular part of the concha completing the posterior ethmoidal sinuses with a superolateral depressed area. It articulates below with the orbital process of the palatine bone. It also shows a smooth and triangular inferomedial area constituting part of the nasal roof.

 

Sphenoidal Concha Posterior Part

Horizontal triangular part of the concha facing the nasal cavities, completing the sphenopalatine foramen and constituting part of the floor of the sphenoid sinus. Its medial edge forms the rostrum of the sphenoid in the midline, joining the contralateral one. Its apex is posteriorly directed and superomedial to the vaginal process. Both the posterior part of the concha and the vaginal process articulate with the ala of the vomer.

 

Sphenoidal Crest

A protrusion located where the anterior parts of the two conchae joins in the midline.

 

Sphenoidal Rostrum

The midsagittal process located where the posterior parts of the sphenoidal conchae joins, inferior to the sphenoidal crest.

 

Sphenoid Sinus Ostium

The hole that connects the sphenoid sinus with the spheno-ethmoidal recess, piercing the upper portion of the smooth area of the anterior part of the sphenoidal concha.

 

Sphenoid Spine

The spine projecting inferiorly from the greater wing posterior to the foramen spinosum. Its tip gives attachment to the spheno-mandibular ligament.

 

Sulcus Tubae

The sulcus located inferior to the posterior margin of the greater wing, containing the cartilaginous pharyngo-tympanic tube. It is completed by the sphenoid spine, laterally, and the petrous part of the temporal bone, posteromedially.

 

Superior Orbital Fissure

The approximately triangular aperture connecting the cranial cavity and the orbit. Its medial border is constituted by the body of the sphenoid. Its superior border is determined by the lesser wing, and supero-laterally, between the greater and the lesser wings, by the frontal bone. Its inferior border corresponds to the medial margin of the orbital surface of the greater wing of the sphenoid. It is traversed by: the lacrimal, frontal, and IV cranial nerves, the superior ophthalmic vein, and the recurrent meningeal branch arising from the lacrimal artery passing outside the annulus of Zinn; the nasociliary, abducent, and superior and inferior divisions of the III cranial nerves passing inside the annulus of Zinn.

 

Tuberculum Sellae

The bony elevation posterior to the prechiasmatic sulcus, comprised between the lateral tubercular crests, which reach the middle clinoid processes. It constitutes the superior border of the anterior wall of the sella turcica, and gives insertion to the diaphragma sellae.

 

Vaginal Process

Thin bony projection arising medially from the base of the medial pterygoid plate and below the posterior part of the rostrum.

 

Vidian Canal

The canal whose posterior end is located in the posteromedial margin of the greater wing, at the anterior margin of the foramen lacerum, above and between the pterygoid plates of the sphenoid bone. Its anterior end is on the posterior surface of the pterygopalatine fossa. It houses the Vidian nerve, and accompanying blood vessels. Synonym: Pterygoid canal.

 

References

Anatomy of the Human Body. Gray, H. Philadelphia: Lea & Febiger, 1918; Bartleby.com, 2000

Rhoton's Cranial Anatomy and Surgical Approaches. Rhoton AL. Lippincott Williams & Wil-kins; 2007

Transsphenoidal Approaches: Endoscopic, in Cappabianca P, Iaconetta G, Califano L (eds): Cranial, Craniofacial and Skull Base Surgery. Cappabianca P, Cavallo L, Esposito I, Tschabitscher M, Springer Milan, 2010, pp 197-212 

Paranasal sinuses: anatomic terminology and nomenclature. Stammberger HR, Kennedy DW, Anatomic Terminology G. Ann Otol Rhinol Laryngol Suppl 167:7-16, 1995  

Anatomy and CT reconstruction of the anterior area of sphenoid sinus. Wang S, Zhang J, Xue L, Wei L, Xi Z, Wang R. Int J Clin Exp Med 8:5217-5226, 2015 

A mental hook for learning the three-dimensional anatomy of the sphenoid bone: an angelic resemblance. Gangata H Br. J Oral Maxillofac Surg 48:e27-28, 2010 

Surgical anatomy of the sphenoid sinus. Elwany S, Yacout YM, Talaat M, El-Nahass M, Gunied A, Talaat M, J Laryngol Otol 97:227-241, 1983

   

Authors

 

Francesco Belotti, MD

Neurosurgery Resident
University of Brescia (Italy) 
"Spedali Civili" Hospital Brescia (Italy) 
Scientific Team - UpSurgeOn

 

Federico Nicolosi, MD

Neurosurgeon
University of Milan
"Spedali Civili" Hospital Brescia (Italy)
Scientific Team - UpSurgeOn


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