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

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Temporal Bone

The temporal bone contributes to the lateral skull base, the lateral wall of the skull, and the zygomatic arch. It consists of the four following parts: the flat, vertical squamous part, which is the largest part, showing a medial and a lateral surfaces; the posteroinferior mastoid part, which gives insertion to the muscles of the neck and has a pneumatization in communication with the middle ear; the petrous part, located between the greater wing of the sphenoid and the clivus, containing the middle and inner ears, the VII cranial nerve together with the VIII, and the internal carotid artery; and the thin plate of bone called tympanic part, which surrounds the base of the styloid process. The temporal bone articulates with the sphenoid, occipital, parietal, and zygomatic bones.

 

Parts

 

Mastoid part

It is the posteroinferior part of the bone and presents an anteroinferior projection, namely the mastoid process, which is larger in adult males. The mastoid foramen is present posteriorly on the lateral surface of the mastoid part. The extracranial medial surface is marked by the mastoid notch and the occipital groove. The intracranial medial surface of the mastoid part is grooved by the sulcus for the sigmoid sinus, and grooves for meningeal branches of the occipital artery may be observed near the intracranial opening of the mastoid foramen.

 

Squamous part

The thin anterosuperiorly located part, the external surface of which forms the medial wall of the temporal fossa, giving attachment to the temporalis muscle, and that is grooved by the middle temporal artery. The supramastoid crest, the suprameatal triangle, and the suprameatal spine (of Henle) are visible on the external surface. Occasionally, the squamo-mastoid suture can be seen approximately 1.5 cm below the supramastoid crest, and rarely the foramen for the petrosquamous sinus may persist above the posterior root of the zygomatic process. The concave internal surface of the squamous part is marked by the convolutions of the temporal lobe and the groove for the middle meningeal artery. The superior edge of the squama overlaps with the inferior border of the parietal bone. The inferior edge is rough internally and the anterior edge is rough externally in order to articulate with the greater wing of the sphenoid bone.

 

Tympanic part

The curved plate anterior to the mastoid process and inferior to the squamous part surrounding the external acoustic meatus. It fuses internally with the petrous part and posterosuperiorly with the squamous and mastoid parts. Anteriorly, the tympanic part is approximately rectangular constituting the tympanic plate, the medial part of which contributes to the squamo-tympanic fissure. The downward directed tegmen tympani protrudes as a crest from the squamo-tympanic fissure splitting it into petro-squamosal and petro-tympanic fissures. The sharp inferior edge of the tympanic part forms the vaginal process surrounding the base of the styloid process. The stylomastoid foramen is located between the styloid and the mastoid processes.

 

Styloid process

It arises from the inferior aspect of the temporal bone, typically showing an antero-medial concavity, and gives attachment to muscles and ligaments. Its dimension is variable, and its length can range between a few mm up to the average length of 25 mm.

 

Zygomatic process

It arises from the lower region of the squamous part with two roots, and projects anteriorly to articulate with the zygomatic bone. The inferior surface of the anterior root presents the articular tubercle, and its anterior border is in continuity with the infratemporal crest on the greater wing of the sphenoid bone. The mandibular fossa is visible posterior to the articular tubercle. Its anterior articular surface is separated from the posterior tympanic surface by the postglenoid tubercle. The squamo-tympanic fissure separates the mandibular fossa from the tympanic part. The posterior root continues posteriorly into the supramastoid crest.

 

Petrous part

It is pyramid-shaped and wedges between the sphenoid and occipital bones. It contains the vestibular and the cochlear systems, the facial canal, and the carotid canal. It presents the anterior, posterior, and inferior surfaces that project anteromedially towards the apex, which constitutes the posterolateral border of the foramen lacerum. The anterior opening of the carotid canal pierces the apex of the petrous part.

Anterior Surface

The anterior surface contributes to the floor of the middle cranial fossa, and is separated from the internal surface of the squama by remnants of the petro-squamosal suture, while the posterior surface faces the posterior cranial fossa. The trigeminal impression is located posterior to the apex, and anterior to the internal acoustic meatus and the bone overlying the cochlea. The arcuate eminence arises from the anterior surface of the petrous part. The tegmen tympani is the part of the anterior surface contained between the squama and the arcuate eminence. The foramina for the greater and lesser petrosal nerves pierce the anterior surface of the petrous part anterior to the arcuate eminence, and are in continuity with grooves for the same nerves.

Posterior Surface

The posterior surface of the petrous part is pierced by the internal acoustic meatus and the vestibular canaliculus. The subarcuate fossa is visible posterior to the internal acoustic meatus, and it is pierced by the subarcuate canal. 
The superior border, located between the anterior and the posterior surfaces, gives insertion to the tentorium cerebelli, and is grooved by the superior petrosal sinus. 

inferior Surface

The inferior surface of the petrous part gives insertion to the levator veli palatini and the cartilaginous pharyngo-tympanic tube, completing the sulcus tubae on the sphenoid bone, and it articulates with the occipital bone owing to the fibrocartilage that fills the petro-occipital fissure. The anterolateral part of the inferior surface is pierced by the canals for the tensor tympani and the pharyngo-tympanic tube. The opening of the carotid canal and the jugular fossa are visible posteriorly on the inferior surface. The tympanic canaliculus pierces the inferior surface between the carotid canal and the jugular fossa. The cochlear canaliculus is located on the edge of the jugular fossa at the level of the anterior border of the petrous part, and the mastoid canaliculus is located laterally in the jugular fossa.
The posterior border, located between the inferior and the posterior surfaces, is grooved by the inferior petrosal sinus, and contributes to the jugular foramen. The anterior border, located between the inferior and the anterior surfaces, articulates with the greater wing of the sphenoid bone.

 

Articulations

The temporal bone articulates with the sphenoid, occipital, parietal, and zygomatic bones.

 

Skeletal Landmarks

The tip of the mastoid process can be palpated behind the acoustic meatus. The lateral wall of the mastoid antrum corresponds to the suprameatal triangle, which is bounded by the posterosuperior margin of the acoustic meatus, the supramastoid crest, and a vertical line tangent to the posterior border of the acoustic meatus.

 

Anatomical Details

Arcuate Eminence

The convexity bulging from the superior surface of the petrous part. It corresponds to the position of the superior semicircular canal.

 

Articular Tubercle

The inferiorly directed semi-cylindrical convexity of the anterior root of the zygomatic process. It faces the temporo-mandibular joint, and is contact with the articular disc.

 

Carotid Canal

The canal that houses the internal carotid artery in its course from the neck to the cavernous sinus. Its anterior opening is at the apex of the petrous part, which is the posterolateral limit of the foramen lacerum. Its posterior opening is on the inferior surface of the petrous part. The carotid, which enters the temporal bone almost vertically, turns anteromedially during its course inside the bone to reach the apex.

 

Cochlear Canaliculus

A small canaliculus, housing the perilymphatic duct and a vein draining from the cochlea to the internal jugular vein, located anteromedial to the jugular fossa, and inferior to the internal acoustic meatus.

 

External Acoustic Meatus

The bony part of the external ear, that is located lateral to the middle ear. Its anterior wall, floor, and part of the posterior wall are formed by the tympanic part of the temporal bone. It is inferior to the squamous part, and anterior to the mastoid part of the temporal bone.

 

Greater Petrosal Nerve Foramen

A hole on the superior surface of the petrous part, anterior to the arcuate eminence. It is the exit point of the greater petrosal nerve, which branches from the facial nerve at the level of the geniculate ganglion.

 

Greater Petrosal Nerve Groove

The impression of the greater petrosal nerve on the petrous part, from the greater petrosal nerve foramen to the anterior opening of the carotid canal, where it joins the deep petrosal nerve forming the Vidian nerve.

 

Inferior Petrosal Sinus Sulcus

The notch on the posterior edge of the petrous part forming, together with the occipital bone, a sulcus for the inferior petrosal sinus.

 

Internal Acoustic Meatus

The opening, approximately at the center of the posterior surface of the petrous part, that gives access to the inner ear, and is traversed by the VII and VIII cranial nerves, together with the labyrinthine artery.

 

Jugular Fossa

The fossa behind the inferior petrosal sinus sulcus contributing with the occipital bone to form the jugular foramen.

 

Lesser Petrosal Nerve Foramen

A hole on the superior surface of the petrous part, anterior to the arcuate eminence, and lateral to the grater petrosal nerve foramen. It is the exit point of the lesser petrosal nerve, which arises from the tympanic plexus at the level of the middle ear.

 

Lesser Petrosal Nerve Groove

The impression of the lesser petrosal nerve on the petrous part, from the lesser petrosal nerve foramen to the foramen ovale, through which it exits the cranial cavity to reach the otic ganglion.

 

Mandibular Fossa

The fossa that houses the articular disk and the condyle of the mandible in the temporo-mandibular joint. It is limited anteriorly by the articular eminence, and posteriorly by the tympanic part of the temporal bone.

 

Mastoid Canaliculus

The canaliculus located in the lateral aspect of the jugular fossa, containing the auricular branch of the vagus nerve.

 

Mastoid Foramen

The variable foramen traversing the mastoid part of the temporal bone. It contains an emissary vein from the sigmoid sinus and a small dural branch of the occipital artery. In most cases, it is located just anterior to the posterior border of the mastoid part, although it can pierce the occipital bone or the occipito-mastoid suture, or it can be absent.

 

Mastoid Notch

A deep notch on the inferomedial surface of the mastoid process, lateral to the occipital groove for the occipital artery. It gives attachment to the digastric muscle. Synonym: Digastric notch.

 

Mastoid Process

The round, inferiorly directed process of the mastoid part of the temporal bone. It gives attachment to the longissimus capitis, splenius capitis, and sternocleidomastoid muscles on its lateral surface. It is larger in adult males.

 

Middle Meningeal Artery Groove

The impression of the middle meningeal artery on the internal surface of the squama of the temporal bone.

 

Middle Temporal Artery Groove

The impression of the middle temporal artery on the external surface of the squama of the temporal bone, superior to the external acoustic meatus.

 

Occipital Artery Meningeal Branch Groove

A small faint groove that can be visible arising from the internal end of the mastoid foramen. It bears the meningeal branch of the occipital artery.

 

Occipital Groove

The groove on the inferior surface of the mastoid part of the temporal bone, medial to the mastoid notch, bearing the occipital artery.

 

Petro-squamosal Fissure

The remainder of the suture between the petrous and the squamous parts of the temporal bone that fuse during the ossification process. Its traces are visible between the inferior border of the squamous part and the crest of the tegmen tympani arising from the petrous part. It is separated from the petro-tympanic fissure by the same crest.

 

Petro-squamosal Suture

The faint remainder of the suture between the petrous and the squamous parts of the temporal bone that fuse during the ossification process. It can be visible between the superior surface of the petrous part and the internal surface of the squamous part.

 

Petro-tympanic Fissure

The remainder of the suture between the tympanic and the petrous parts of the temporal bone that fuses during the ossification process. Its traces are visible inferiorly between the tympanic part and the crest of the tegmen tympani arising from the petrous part. It is separated from the petro-squamosal fissure by the same crest. It is traversed by part of the anterior ligament of the malleus, the anterior tympanic branch of the internal maxillary artery, and the chorda tympani arising from the facial nerve.

 

Pharyngo-tympanic Tube

The inferior of the two canals leading to the tympanic cavity that are visible at the junction between the squamous and the petrous parts of the temporal bone. It is the bony part of the Eustachian tube and opens into the tympanic cavity.

 

Post-glenoid Tubercle

The conical, lateral tubercle, inferior to the posterior root of the zygomatic process, separating the articular surface of the mandibular fossa from the tympanic plate.

 

Sigmoid Sinus Sulcus

The curved impression of the sigmoid sinus on the internal surface of the mastoid process. Its floor is constituted by a thin layer of bone separating it from the mastoid air cells.

 

Squamo-mastoid Suture

The faint remainder of the suture between the mastoid and the squamous parts of the temporal bone that fuse during the ossification process. It can be visible between the lateral surfaces of the mastoid and the squamous parts.

 

Squamo-tympanic Fissure

The remainder of the suture between the tympanic and the squamous parts of the temporal bone that fuse during the ossification process. Its traces are visible between the inferior border of the squamous part and the tympanic part. It is divided into petro-squamosal and petrotympanic fissures by the crest of the tegmen tympani.

 

Styloid Process

A pointed, variably long, anteroinferiorly directed process arising from the inferior aspect of the temporal bone. It usually shows an anteromedial concavity, although its curvature may vary. Its base is covered by a thin sheath from the tympanic plate; while its tip gives attachment to the styloglossus, stylohyoid, and stylopharyngeus muscles, and to the stylohyoid and stylomandibular ligaments.

 

Stylomastoid Foramen

The foramen located between the styloid and the mastoid processes constituting the external end of the facial canal. It is traversed by the facial nerve and the stylomastoid artery.

 

Subarcuate Canal

The small canal connecting the posterior cranial fossa to the mastoid antrum the mastoid antrum. It contains the subarcuate artery and vein.

 

Subarcuate Fossa

A depression on the posterior surface of the petrous part, located slightly superior to and between the internal acoustic meatus and the vestibular canaliculus.

 

Supramastoid Crest

The crest curving posterosuperiorly as the continuation of the posterior root of the zygomatic process. It crosses the posterior part of the squama, above the external acoustic meatus. It gives attachment to the deep temporal fascia.

 

Suprameatal Spine

The spine located inside the suprameatal triangle, just above the posterosuperior edge of the external acoustic meatus. Synonym: Spine of Henle.

 

Suprameatal Triangle

A triangular depression laying between the anterior end of the supramastoid crest and the posterosuperior quadrant of the external acoustic meatus. It constitutes the surface projection of the mastoid antrum.

 

Tegmen Tympani

The superior surface of the petrous part, constituting the roof of the tympanic cavity.

 

Tegmen Tympani Crest

The crest arising from the petrous part and reaching the inferior surface of the temporal into the squamo-tympanic fissure. It divides that fissure into petro-squamosal and petro-tympanic fissures.

 

Tensor Tympani Canal

The superior of the two canals leading to the tympanic cavity that are visible at the junction between the squamous and the petrous parts of the temporal bone. It houses the tensor tympani muscle.

 

Trigeminal Impression

The impression of the trigeminal ganglion on the superior border of the petrous part, behind its apex.

 

Tympanic Nerve Canaliculus

A canaliculus laying on the ridge between the jugular fossa and the carotid canal. It is traversed by the tympanic nerve arising from the glossopharyngeal nerve.

 

Tympanic Plate

The curved plate of bone of the tympanic part inferior to the squamous part and anterior to the mastoid process, to which it merges superiorly and posteriorly, respectively. It constitutes the posterior wall of the mandibular fossa, forming also the anterior wall, the floor, and part of the posterior wall of the external acoustic meatus.

 

Vaginal Process

The inferior border of the tympanic part splitting to form the sheath of the styloid process.

 

Vestibular Canaliculus

The canal located posterior to the internal acoustic meatus. It contains the endolymphatic sac and duct, together with small artery and vein.

 

Zygomatic Process

The process projecting anteriorly from the inferior portion of the squamous part. Its posterior, laterally directed base is triangular-shaped with superior and inferior surfaces, and anterior and posterior roots. The process turns anteromedially to reach the temporal process of the zygomatic bone and complete the zygomatic arch.

 

Zygomatic Process Anterior Root

The anterior root of the zygomatic process projecting horizontally from the squamous part. It is located above the articular tubercle.

 

Zygomatic Process Posterior Root

The posterior root of the zygomatic process projecting forwards from the supramastoid crest.

 

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

Surgical anatomy of the temporal bone: an atlas. Chan LL, Manolidis S, Taber KH, Hayman LA, Neuroradiology 43:797-808, 2001 

Anatomy of the temporal bone. Gunlock MG, Gentry LR. Neuroimaging Clin N Am 8:195-209, 1998 

 

 

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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