ANATOMY OF TEMPORAL BONE

BY Dr. VIJAY KUMAR

The paired temporal bones contribute to both the base and the lateral wall of the skull.

For cranial cavity each forms part of the middle and posterior cranial fossae.

Each bone is divisible into the following four parts:

1.Squamous 2.Mastoid 3.Petrous 4.Tympanic When the pores of the

external acoustic meatus is taken as a point of topographical referrence,the squamous part is directed upward

the mastoid part backward

the tympanic forward and downward

the petrous portion medially.

Masto

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The temporal bone articulates with :

Sphenoid bone Parietal bone Occipital bone Zygomatic bone.

Parietal

bone

Occipital

bone Temporal

boneZygoma tic

The Squamous Part

The squama is a vertical plate,the semicircular free border of which is serrate on anterosuperior portion and bevelled from within.

The Lateral Surface: It is smooth and gives

attachment to temporalis muscle.

zygomatic process projects from the lower part of the surface for attachment of masseter muscle.

Mandibular fossa is situated below the root of the zygomatic process.

The sulcus for middle temporal artery passes upward on the posterior part of the squama.

The medial surface: is directed towards the middle cranial fossa presents with impressions for the cerebral sulci and gyri and a deep sulcus for the middle meningeal artery.

The Mastoid PartThis is a thick

conical projection from the squamous and petrous parts of the temporal bone and it comes into appostion with occipital and parietal bones

The lateral surface: is rough and gives attachment to posterior auricular and occipital muscles.

It has one or more foramina(Mastoid foramen) for transmission of the mastoid branch of occipital artery and the mastoid emissary veins to sigmoid sinus.

A small spur ,the suprameatal spine of Henle , projects laterally from the posterosuperior margin of the external acoustic meatus.

The slightly depressed surface behind the spine is mastoid fossa,it is perforated by numerous blood vessels.

A thick downward directed portion,the mastoid process,gives attachment to the musculature of shoulder girdle and of the back.

The medial surface:

presents a deep groove ,the sigmoid sulcus for lodgement of the sigmoid venous sinus of the dura mater.

Within the process are numerous cavities,the mastoid air cells lined by mucous membrane that is continuous with that of tymanic cavity.

The petrous partThis part of the temporal bone is

like a three sided pyramid.The base united with the mastoid

part is inserted into the angle between occipital and sphenoid bones.

The apex is directed medially and forward.

The foramen lacerum intervenes between the apex and the sphenoid bone .Structure passing whole length: Meningeal branch of ascending pharyngeal arteryEmissary veins

Other structure partialy traversing is : Internal carotid artery with venous and sympathetic plexus around it.Greater petrosal nerve unite with dep petrosal nerve to form nerve to pterygoid canal

The petrous part…

The Petrous part has got three surfaces: AnteriorPosteriorInferior.

The anterior surface: It is smooth , forms part of the

middle cranial fossa and inclines forward and downward.

Laterally it is fused with squama at the petrosquamous suture.

The petrous part…

The petrous part…The anterior margin(termed the

anterior angle) is free & roughened , with the greater wing of the sphenoid bone bounds an opening : the musculotubal canal

Canal is subdivided by leaflet of bone into smaller upper part - the semicanal for the tensor tympani muscle

and a large lower portion the semicanal of

auditory(eustachian ) tube

Near the middle of the anterior surface is the Arcuate eminence ,caused by underlying superior semicircular canal.

Anterior and lateral to this eminence is the tympanic tegmen,which forms the roof of the tympanic cavity.

VIJAY

Tympanic tegmen

In the anterior direction near the apex is a medial opening, hiatus of the facial canal

(it transmits the superficial petrosal branch of the middle meningeal artery and the greater superficial petrosal nerve)

and a lateral smaller opening, superior

aperture of the tympanic canaliculus(it transmits the superior tympanic artery and the lesser superficial petrosal nerve)

The posterior surface: It lies in an almost vertical plane and

it faces the posterior cranial fossa.It is bounded above at the superior

angle by the sulcus for superior petrosal sinus,

below at the posterior angle ,the pyramid unites with the occipital bone ,along the line of fusion accommodating the sulcus for inferior petrosal sinus.

Midway between the base and apex is the opening of internal acoustic meatus(short canal for acoustic and facial nerves and the internal auditory blood vessels)

Behind and above this is the subarcuate fossa (it carries blood vessels to otic capsule during fetal life.) it is of pin point caliber in adults and may transmit small veins to dura mater.

Further laterally and downward is the vestibular aqueduct (for transmission of endolymphatic duct and sac)

The inferior surface : The inferior surface of pyramid lies in

horizontal plane.With occipital bone this surface forms the

jugular foramen

The lateral part of the foramen contains the junction of sigmoid sinus and the internal jugular vein

Medial part contains inferior petrosal sinus and middle portion contains cranial nerves IX,X and XI.

In front of the lateral compartment of the foramen is jugular fossa (for the bulb of jugular vein).

Medial to fossa is the funnel-shaped external aperture of the cochlear canaliculus (containing perilymphatic duct).

In front of the fossa is the external carotid foramen(entrance to the canal for the internal carotid artery and its plexus of veins and sympathetic nerves.)

Near the external carotid foramen small openings ,the caroticotympanic canaliculi are present which transmit the caroticotympanic artery and nerves into the middle ear.

The external carotid foramen is separated from the jugular fossa by the carotid ridge.

On the edge of the carotid ridge is petrosal fossula for lodgement of petrosal ganglion of the glossopharyngeal nerve.

At the bottom of this fossula ,tympanic canaliculus is situated ,which transmits tympanic branch of glossopharyngeal nerve (Jacbson’s nerve) and tympanic branch of ascending pharyngeal artery.

Rough jugular surface behind the jugular fossa articulates with the jugular process of the occipital bone.

Lateral to this surface,a downward directed cylindrical spur ,the styloid process is present.

The stylomastoid foramen is present at its base on the posterior aspect.

This is the external orifice of the facial canal and transmits the facial nerve ,the stylomastoid artery and in some cases the auricular branch of the vagus nerve.

Mastoid incisure/notch (for the attachment of the digastric muscle) and the temoral/occipital groove(for the occipital artery) is present in the posterior direction.

The Tympanic PartThe tympanic bone is thin and

roughly quadrilateral bone.It is hollow above and concave in

front and below.It forms all the anterior and inferior

wall and part of posterior wall of the external acoustic meatus.

The posterosuperior surface faces the external acoustic meatus and the tympanic cavity.

The middle of anteroinferior surface is thin & sometimes presenting a small Foramen of Huschke.

It represents a nonossified portion of the plate.

At the medial end a groove called tympanic sulcus is present whichh is deficient superiorly ,the tympanic membrane is present in this sulcus.

The inferior surface is prolonged into a vaginal process,which encircles the lateral aspect of the base of the styloid process.

Sutures and Articulations Articulations: The temporal bone articulates with:occipital parietalSphenoidzygomatic bones and – by a movable

joint- with the mandible.Articulations are formed also with the

auditory ossicles and the hyoid bone through the ligaments.

Embryology and OssificationThe skull is developed from the mesenchyme

surrounding the developing brain.Some of the bones of skull are formed in

membrane, some in cartilage and some partly in membrane and partly in cartilage.

The squamous and tympanic parts of the temporal bone develop in membrane while the petrous part in the cartilage.

The squamous portion of the subsequent temporal bone is formed from one(or two) ossification centers which arise in membrane in the second month of intrauterine life.

The tympanic portion has three ossification centers which appear by ninth to tenth fetal week.

The tympanic and squamous part unite by ninth month of fetal life.

The petrous bone by the fifth month is represented by the otic capsule. This bone later ossifies in 14 centers. (petrous part is formed in cartilage.)

squamous and petrous part fuse immediately after birth.

The styloid process (formed in cartilage) ossifies from six months onwards.

Zygomatic bone arises as a thin bony plate by ossification in membrane at the end of second month of embryonic life.

Applied anatomy and important relationsGlossopharyngeal nerve lies in close relation to

styloid process and Elongated styloid process or calcified stylohoid ligament may lead to Eagle’s syndrome or styalgia.(characterised by pain in tonsillar fossa and upper neck , radiating to ipsilateral ear and aggravated on swallowing)

Mac Ewen’s triangle is a landmark for mastoid antrum and is formed by posterosuperior wall of external acoustic meatus ,the posterior extension of the root of zygomatic arch and a tangent to it joining external auditory canal.

The position of sigmoid sinus in the sigmoid sulcus just behind and deep to the mastoid antrum makes it vulnerable to damage in mastoid surgeries.

The anterior relation of temporomandibular joint to external acoustic meatus is important as over enthusiastic attempts at straightening the anterior canal wall can lead to sagging of head of mandible in external auditory canal.

And for the same reason a backward directed force on the mandible can cause trauma and bleeding in external auditory canal(either unilateral or bilateral)

The intratemporal course of the facial nerve from the entrance of facial canal at the fundus of internal acoustic meatus to the stylomastoid foramen is extremely important in ear surgeries.

The horizontal semicircular canal ,the processus cochleariformis , the oval window , the pyramid , the aditus , digastric ridge and the short process of incus are few important landmarks which help to identify the position and course of facial nerve in the temporal bone.

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