The temporal bone (os temporale) is a paired bone forming the lateral part of the base of the skull and it contains the organs of hearing and equilibrium. It has three parts (squamous part, petrous part, and tympanic part).
The squamous part (pars squamosa)contributes to the formation of the lateral walls of the skull. It has two surfaces :
- Cerebral surface (facies cerebralis) which marks impressions for cerebral gyri (impressiones digitatae).
- Temporal surface (facies temporalis).
The squamous part has the following features:
- Groove for middle temporal artery (sulcus arteriae temporalis mediae).
- Zygomatic process (processus zygomaticus), which projects anteriorly and passes forward to join the zygomatic bone and form the zygomatic arch(arcus zygomaticus).
- Supramastoid crest (crista supramastoidea).
- Suprameatic foveola or suprameatal triangle (foveola suprameatica).
- Suprameatal spine (spina suprameatica).
- Mandibular fossa (fossa mandibularis) for articulation with the mandible by the articular surface (facies articularis) and the articular tubercle (tuberculum articulare), which prevents anterior dislocation of the head of the mandible when the mouth is opened.
The squamous part has an articular tubercle which is surrounded by the:
- Petrotympanic fissure (fissura petrotympanica) also called as Glaser’s fissure.
- Petrosquamous fissure (fissura petrosquamosa).
- Tympanosquamous fissure (fissura tympanosquamosa).
- Tympanomastoid fissure (fissura tympanomastoidea).
The squamous part has two borders:
- Parietal margin (margo parietalis) with parietal notch (incisura parietalis).
- Sphenoidal margin (margo sphenoidalis).
The squamous suturelies between the parietal bone and the squamous part of the temporal bone.
The petrous part (pars petrosa, Gr. petros =stone) consists of two main portions. The medial portion is called the “pyramid” because of its pyramidal shape with the apex facing anteromedially. The posterior portion is called mastoid process.
The pyramid has three surfaces (anterior surface, posterior surface, and inferior surface).
Anterior surface of the pyramid (facies anterior partis petrosae)which partly formes the floor of the middle cranial fossa. It has the:
- Trigeminal impression (impressio trigeminalis) which is a small depression on the superior surface of the apex, it contains the ganglion of the trigeminal nerve.
- Arcuate eminence (eminentia arcuate) which forms the roof of the tympanic cavity called tegmen tympani(tegmen tympani).
- Groove for the greater petrosal nerve (sulcus nervi petrosi maioris) with the:
- Hiatus and canal for the greater petrosal nerve (hiatus et canalis nervi petrosi maioris).
- Groove for the lesser petrosal nerve (sulcus nervi petrosi minoris) with the:
- Hiatus and canal for the lesser petrosal nerve (hiatus et canalis nervi petrosi minoris).
- Superior border of the petrous part (margo superior partis petrosae) with the:
- Groove for the superior petrosal sinus (sulcus sinus petrosi superioris).
- Musculotubal or musculotubarine canal (canalis musculotubarius)which leads to the tympanic cavity. It is divided by a septum (septum canalis musculotubarii) into the:
- Semicanal of tensor tympani muscle (semicanalis musculi tensoris tympani) which is smaller of the two muscles, yet equally important.
- Semicanal of acoustic tube (semicanalis tubae auditivae) which is the larger one. It is the bony part of the auditory tube for the conduction of air from the pharynx to the tympanic cavity.
Posterior surface (facies posterior partis petrosae) faces posteriomedially and forms part of the anterior wall of the posterior cranial fossa. It has the:
- Internal acoustic opening (porus acusticus internus) which extends as the internal acoustic meatus (meatus acusticus internus). It transmits the facial, vestibulocochlear nerve and the internal auditory artery and veins.
- Subarcuate fossa (fossa subarcuata) is located inferiorly to the arcuate eminence. It is most prominent in the fetus. In the adult it lodges a process of dura and a small artery and vein. It could be extended as a blind tunnel beneath the superior semicircular canal.
- Opening of vestibular canaliculus (apertura canaliculi vestibuli) which extends as the vestibular canaliculus (canaliculus vestibulae). It leads to the inner ear giving passage to the endolymphatic duct.
- Posterior border of the petrous part (margo posterior partis petrosae) has the:
- Groove for the inferior petrosal sinus (sulcus sinus petrosi inferioris) visible on its medial part.
- Jugular notch (incisura iugularis) visible on its lateral part.
nferior surface (facies inferior partis petrosae) faces downward and is visible only on the external surface of the base of the skull. There are following features on the inferior surface of the pyramid:
- Jugular fossa (fossa iugularis) which lies medially to the styloid process and presents the:
- Opening of cochlear canaliculus (apertura canaliculi cochleae) which is located posteromedialy to the margin of the fossa. It leads to the inner ear giving passage to the perilymphatic duct.
- Mastoid canaliculus (canaliculus mastoideus) which is located in the lateral part for the entrance of the auricular branch of the vagus nerve.
- Jugular notch (incisura iugularis).
- Intrajugular process (processus intraiugularis).
- Styloid process (processus styloideus) for attachment of the muscles and the ligaments (stylohyoid and stylomandibular).
- Stylomastoid foramen (foramen stylomastoideum) which transmits the facial nerve and one of the arteries
- External opening of the carotid canal (foramen caroticum externum).
- Petrosa fossula (fossula petrosa).
- Canaliculus tympanicus (canaliculus tympanicus).
The mastoid process (processus mastoideus)is the posterior portion of the petrous part of the temporal bone that is situated behind the external acoustic opening. It is conical protuberance of the petrous part with the:
- Mastoid air cells (cellulae mastoidea) which are air spaces inside the process. The tympanic cavity communicates with the mastoid air cells by the mastoid antrum (antrum mastoideum).
- Mastoid notch (incisura mastoidea) which is the place of arising of the posterior belly of digastric muscle.
- Groove for occipital artery (sulcus arteriae occipitalis) which is located closer to the midline.
- Groove for sigmoid sinus (sulcus sinus sigmoidei) which is found on the cerebral surface of the base of the pyramid.
- Mastoid foramen (foramen mastoideum) for the emissary veins.
- Suprameatic spine (spina suprameatum) located above the external acoustic opening.
Clinical comments
Petrous Apex Syndrome (PAS) is an infection arising within or spreading to the apex of the petrous part of the temporal bone. Usually the apex infection occurs as an extension of a middle ear or mastoid process inflammations. It can result in severe clinical consequences because the apex has very close contact to important neural and vascular structures. Furthermore, two of the walls of the petrous part constitute the middle and the posterior cranial fossa. Neuronally, the trigeminal ganglion (CNV) and abducens nerve (CNVI) lie anteriorly to apex. Vascularly, the bulb of the internal jugular vein and inferior petrosal sinus is located at inferior aspect of the petrous part and additionally at the region of the apex, the carotid artery and cavernous sinus is found. PAS or petrous apicitis is a combination with the clinical triad of headache or pain in the temporal or parietal region, abducens nerve palsy, and otorrhea. Prior to the introduction of antibiotics, infections of the apex frequently progressed to meningitis, brain abscess, and cavernous sinus thrombosis.
The tympanic part (pars tympanica) of the temporal bone forms the anterior, inferior, and partly posterior border of the external acoustic meatus (meatus acusticus externus) and external acoustic opening (porus acusticus externus). The external acoustic meatus is a short canal that runs medially and somewhat anteriorly and leads into the tympanic cavity. The external acoustic meatus is incompletely formed in the newborn because the tympanic part forms an incomplete tympanic ring (anulus tympanicus)closed by the tympanic membrane. The tympanic part consists of the:
- Greater tympanic spine (spina tympanica maior)
- Lesser tympanic spine (spina tympanica minor)
- Tympanic notch (incisura tympanica) between the spines
- Tympanic groove (sulcus tympanicus)
- Sheath of styloid process (vagina processus styloidei), which is located around the root of the styloid process.