Anatomy temporal bone

ANATOMY OF
TEMPORAL BONE
MODERATOR – DR. S N MUKHERJEE
PRESENTER - DR. PRANEETH

INTRODUCTION
• Temporal bone is a composite structure
consisting of tympanic bone, mastoid process,
squama and petrosa.
• Styloid process eventhough is closely associated with temporal bone,
is not considered as a part of it.
• From lateral view……, tympanic, squamous and
mastoid portions are seen.
• All these parts are interfaced at their junctions
forming tympano-squamous suture, tympano-
mastoid suture and squamo-mastoid suture.

Tympanic bone
• Tympanic bone forms anterior, inferior and parts of posterior wall of
EAC.
• It constitutes posterior wall of glenoid fossa for TMJ.
• Tympano-mastoid suture is traversed by arnold’s nerve.
• Chorda tympani, anterior process of malleus and anterior tympanic
artery traverse the petro-tympanic fissure.
• Henle’s spine is a projection at
postero-superior aspect of
external auditory canal.

Tympanic bone cont….
• Inferiorly, the vaginal process, a projection of tympanic bone, forms
the sheath of the styloid bone.
• Laterally, tympanic bone borders the cartilaginous EAC and
medially it bears a circular groove called annular sulcus.
• Annular sulcus houses the annulus of TM except
superiorly, where it is deficient called as notch of
rivinus where tympanic membrane
attaches directly to the squama.
• Tympano-squamous and tympano-mastoid sutures are
landmarks for the vascular strip incisions used in
tympanomastoid surgery.

Squamous bone
Squamous portion of temporal bone
forms lateral wall of middle cranial fossa
and interfaces with parietal bone
superiorly, with zygomatic & sphenoid
anteriorly.
Medial surface is grooved by a
sulcus for middle meningeal
artery and lateral surface for
middle temporal artery.

Mastoid bone
• Mastoid portion of temporal bone is the inferiorly extending
projection seen on lateral surface.
• It is composed of squamous portion
laterally and petrous portion medially
separated by petrosquamous korner’s septum.
• Macewen’s triangle (fossa mastoidea) –
linea temporalis, posterosuperior margin of
EAC and a tangent to posterior margin of
EAC. It is a cribrose area having numerous,
perforating small blood vessels. It laterally
overlies the mastoid antrum.

Mastoid bone cont….
• Mastoid foramen, located posteriorly on the mastoid
process, is traversed by a mastoid emissary vein and
1 or 2 mastoid arteries.
• Inferiorly, sternocleidomastoid attaches to mastoid tip.
• Mastoid tip is easily palpable & is landmark for
positioning of postauricular incisions.
• Linea temporalis is an avascular plane due to which
it is an ideal location for the superior limb of ‘T’
musculoperiosteal incision used in the postauricular
approach to the tympanomastoid compartment.

Mastoid bone cont….
• Mastoid process in children is not fully developed, thus cannot be
palpated easily.
• Hence, postauricular incision in children should be given more
horizontally to prevent injury to the facial nerve.

Styloid process
• 2.5 cm in length.
• Slender, pointed piece of bone below
the ear.
• Projects down & forwards from inf
surface of temporal bone.
• Proximal tympanohyal part is ensheathed by vaginal process of
tympanic bone.
• Distal stylohyal part gives attachment to –
• Ligaments – stylohoid & stylomandibular
• Muscles – styloglossus, stylohyoid & stylopharyngeal

Styloid process cont….
• Stylomandibular ligament is a specialised band of
cervical fascia which extends from anterior surface
of apex of styloid process to the posterior surface
of the angle of mandible.
• This ligament separates parotid gland from submandibular gland &
medial pterygoid muscle.
• Eagle syndrome is characterised by recurrent
pain in the oropharynx and face due to
elongated styloid process or calcified
stylohyoid ligament which interferes with
adjacent anatomical structures giving rise to
pain.

Temporal bone cont….
• Petrosa can be seen in superior, medial and posterior views.
• From superior view, landmarks seen are –
• Arcuate eminence (corresponding to sup scc)
• Tegmen tympani
• Foramen spinosum (for middle meningeal art)
• Facial hiatus (marking GPN departure from GG)
• Petrous ridge (sup petrosal sinus resides on it)
• Lesser petrosal nerve + superior tympanic artery = occupies superior
tympanic canaliculus that lies lateral and parallel to the path of GPN to
petrous apex.
• Petrous apex points anteromedially and is marked by the transition of
the intrapetrous to the intracranial ICA, orifice of bony ET & ganglion
of trigeminal nerve in meckels cave anterolaterally.

Arcuate eminence –
• Key landmark in MCF surgeries where IAM can be identified. The bone
anteromedial to AA & GSPN is the meatal plane and lies above the IAC.
It is often marked by a shallow depression.
• In this region, dura is firmly attached on medial side & loosely
attached on lateral side
Meckel’s cave –
• In trigeminal neuralgia cases, glycerol injection is given in gasserion
ganglion located in this area.

• Medial view of temporal bone –
• Porus of IAC
• ICA exits at petrous apex through internal carotid foramen
• Deep sulcus posteriorly – sigmoid portion of lateral venous sinus
• Sulcus at posterior & middle fossa faces of temporal bone – superior petrosal
sinus runs in it.
• Cochlear aqueduct
• Vestibular aqueduct
• Mastoid process
• Styloid process
• Jugular fossa

Posterior view –
• Posterior face of petrosa dominates
• Lies between superior & inferior petrosal sinuses
• It forms ant border of post cranial fossa.
• Landmarks –
• Porus of IAC
• Operculum
• Endolymphatic fossette cradling endolymphatic sac
• Subarcuate fossa

• Sigmoid sulcus is an indentation at the
lateral aspect of post surface and
accommodates sigmoid sinus.
• Anterior to SS, lies the foveate fossa for intradural portion of
endolymphatic sac.
• Operculum, a ledge at the superior extent of the fossa covers
intraosseous portion of endolymphatic sac.
• Vestibular aqueduct runs anteriorly, medially & superiorly from
operculum to end at the medial wall of vestibule.
• Sup petrosal sulcus at the interface between MCF & PCF plates of
temporal bone carries SPS from SS.

Inferior surface –
• Interfaces with sphenoid & occipital
bones.
• Provides attachment for deep muscles of neck
• Jugular fossa – houses jugular bulb, separated from ICA by
jugulocarotid crest.
• Inferior tympanic artery & jacobson’s nerve passing through aperture
of inferior tympanic canaliculus, is seen in the jugulocarotid crest
• Cranial aperture of cochlear aqueduct – anteromedial to jugular fossa
• Groove for inferior petrosal sinus – near petrous apex

• Stylomastoid foramen – posterior to styloid process.
• Occipital artery – occipital groove
• Digastric muscle – mastoid incisure
• Jugular foramen Contents – IX, X, XI cranial nerves + Post meningeal art + Inf
petrosal & sigmoid sinuses.
Medial aspect
of the tip
IJV & JB are removed

• Classically, jugular foramen has been
divided into anteromedial pars nervosa
consisting IX, X, XI CN and posterolateral
pars venosa containing the jugular vein.
• Styloid process lies lateral to jugular
foramen.
• Glomus jugulare tumours are rare, slow-
growing, hypervascular tumors that arise
within the jugular bulb.
• Phelp’s sign – loss of crest of bone as seen
in CT between carotid canal & jugular
canal in glomus jugulare.

• In jugular fossa
• IX CN lies more ant & lat
• X, XI CN are located post & med to IX CN
• CN XI is generally identified as it crosses over IJV in the
neck & lat pr of atlas. Sometimes, it can pass medial to IJV.
• When approached intracranially, IX CN is found in the a
anteromed compartment & X, XI CN are posterolateral.
• Hence it is suggested to consider jugular fossa as a canal rather than
an opening so that the IX CN courses from anteromedial to
anterolateral as it passes out of the skull making X & XI CN lying
posterolateral initially and then posteromedially.

• Hypoglossal canal –
• Located in the anterior portion of occipital
condyle & anteroinferior to the jugular foramen.
• Carries XII cranial nerve that courses medial to
cranial nerve X and inferior to jugular foramen.
Inferior petrosal sinus –
Drains into anterior aspect of jugular bulb.
Runs inferior & medial to IX cranial nerve
Runs superior & lateral to X, XI cranial nerves

Cochlear aqueduct –
• Runs from medial aspect of scala tympani of basal cochlear turn to
terminate anteromedial to the jugular bulb lying parallel & inf to IAC.
• In translabyrinthine CPA tumor surgery, drilling
medial to jugular bulb opens it and CSF flows into
mastoid decompressing CSF pressure.
• IX nerve, inf petrosal sinus are found immediately
inferior to the lateral terminus of it (X & XI also in
some cases).
• Therefore, it can be used as a guide to the lower limits of
IAC dissection in translabyrinthine approach as it allows full
exposure of IAC without risking the lower cranial nerves.

INNER EAR –
• Bony labyrinth houses sensory organs & soft tissue structures of the
inner ear and consists of cochlea, 3 scc & vestibule.
• Bone has 3 layers – inner endosteal, outer periosteal & middle layer
consisting of endochondral and intrachondrial bone.
• Cochlea spirals 2.5 turns about its central axis,
the modiolus and height of it is 5mm.
• Base of cochlea abuts
the fundus of IAC & is
perforated by cochlear
nerve fibres.

• Apex lies medial to tensor tympani muscle.
• Osseous spiral lamina winds around the modiolus and along with
basilar membrane separates scala media from scala tympani.
• Interscalar septum separates adjacent turns of cochlea.
• 3 scc – superior, posterior & lateral are orthogonally
related to one another and arc over a span of 240 degrees.
• Each canal has an ampullated (2mm) & a nonampullated (1mm) end.
• Ampulla is cribrose for passage of nerve fibres.
• Nonampullated ends of posterior & superior
scc fuse to form crus commune.

• All ends open into the vestibule.
• Solid angle – angle formed by the 3 scc
• Trautmanns triangle – bony labyrinth, sigmoid
sinus & superior petrosal sinus are the boundaries.
• Thinning or frank dehiscence of the bone of superior
scc may cause sound or pressure induced vertigo.
• Vestibule is the central chamber of
labyrinth & is 4mm in diameter.
• Medial wall of vestibule – spherical recess for saccule &
elliptical recess for utricle and a cochlear recess for
cochlear duct.

• Mike’s dot – (macula cribrosa superior) :-
passageway for superior vestibular nerve
fibres to the cristae ampullares of lateral and superior scc. It is an
important landmark in translabyrinthine surgery as it corresponds to
the extreme lateral aspect of IAC.
• Fissures in bony labyrinth – 3 in number.
• Fissula ante fenestrum - evagination of the perilymphatic space anterosuperior
to oval window, filled with fibrous tissue & cartilage in adult
• Fossula post fenestrum – perilymphatic evagination posterior to oval window.
• Hyrtle’s fissure (tympanomeningeal hiatus) – embryologic remnant.

• Microfissures – 2 in number.
• 1) between round window niche & ampulla of
posterior scc
• 2) superior & inferior to oval window.
• Microfissures are breaks in the endosteal and enchondral layers of
temporal bone, and filled with fibrous tissue & acellular matrix.
• Hyrtle’s fissure if persistent is a route of CSF leakage into ME.
• Other fissures are hypothesised to be the routes of perilymph leakage.

• Membranous labyrinth consists of cochlear duct,
3 scd & their cristae ampullares, otolithic organs like utricle & saccule,
endolymphatic duct & sac.
• Space between bony & membranous labyrinths are filled with
connective tissue, blood vessels, perilymph + s.tympani, s.vestibuli,
perilymphatic cistern of vestibule, perilymphatic duct, perilymph
spaces surrounding the scd.
• Endolymphatic duct originates in med wall of vestibule.
• It first parallels crus commune & then posterior scc as
it heads to endolymphatic sac, anterior & medial to
sigmoid sinus.

• Endolymphatic sac lies 10mm inferior & lateral to porus of IAC. It has
an intraosseous portion covered by operculum and a more distal
intradural portion.
• Donaldson’s line – a surgical landmark in endolymphatic sac surgery, is
derived by extending the plane of the lateral scc so that it bisects the
posterior scc and contacts the posterior fossa dura. Endolymphatic sac
lies inferior to this line.

IAC –
• Contents – superior & inferior vestibular nerves, cochlear nerve, facial
& intermediate nerves, labyrinthine artery & vein.
• 3.4mm diameter, 8mm length.
• Porus – PCF opening & fundus – labyrinth opening.
• At the fundus -

• The nerves rotate as we progress medially, with
fusion of the cochlear & vestibular nerves.
• Facial nerve comes to lie anterior to
vestibulocochlear bundle
• Cochlear nerve moves to lie inferior to the
vestibular nerve.
• Bill’s bar – important landmark in translabyrinthine
surgery of CPA tumor as it separates SVN from
anteriorly located facial nerve.

NEUROANATOMY
TRIGEMINAL NERVE –
• Gasserian ganglion of trigeminal
nerve occupies meckel’s cave on
middle cranial fossa face of the
temporal bone, anterolateral to the petrous apex.
SUP VIEW
SAGITTAL VIEW

NEUROANATOMY cont….
ABDUCENS NERVE –
• Abducens nerve runs in dorello’s canal beneath
posterior petroclinoid (gruber’s) ligament.
• Petrous apicitis can manifest with purulent
otorrhea, retro-orbital pain and VI nerve palsy.

FACIAL NERVE –
• Innervates structures derived
from Reichert’s cartilage.
• 3 nuclei give rise to its fibres –
• Motor nucleus in caudal pons
• Superior salivatory nucleus dorsal to motor
nucleus
• Nucleus tractus solitarius in medulla
oblongata
• Superior aspect of the motor nucleus that
innervates frontalis and orbicularis oculi,
receives input from both sides but
inferior portion receives only ipsilateral
input.

• 5 fibre types make up the
trunk of the facial nerve.
• SVE – facial expression,
stapedius, stylohyoid, digastric
post belly
• GVE – lacrimal, nasal cavity
seromucinous, submaxillary,
sublingual
• Taste ( sensory ) fibres from
ant 2/3rd tongue, tonsillar
fossae, posterior palate
• Somatic sensory from EAC &
concha
• Visceral afferent from mucosa
of nose, pharynx, palate.

Course of the facial nerve is divided into 5 segments.
• Intracranial segment – 24mm from pons to the porus of IAC
• Intracanalicular segment – traverses IAC, occupies anterosuperior
quadrant at fundus where it is joined by nervus intermedius.
• Intralabyrinthine segment – shortest, 4mm, from beginning of
fallopian canal to the geniculate ganglion.
• Tympanic segment – 13mm long, courses in the medial wall of
the tympanic cavity, superior to the cochleariform process & oval
window.
• Mastoid segment – 20mm, from 2nd genu (at lat scc) to
stylomastoid foramen.

Anomalous courses –
• Tympanic segment may be anterior and inferior to oval window.
• Mastoid segment may bulge more posteriorly & laterally than usual.
• Vertical segment may be bi or tripartite.
Fallopian canal dehiscences –
• Most likely site is tympanic segment over oval window.
Subarachnoid space –
• extends till junction of labyrinthine & tympanic segments.
• Occasionally it extends into GG or rarely into tympanic segment.

• CSF otorrhea may occur in such cases as proposed by
Gacek.
Branches of facial nerve –
• Intratemporal –
• Greater petrosal nerve – arises from anterior
aspect of GG & emerges onto floor of MCF via
the facial hiatus.
• Nerve to stapedius – arise from mastoid
segment near pyramid.
• Chorda tympani – 6mm proximal to
stylomastoid foramen.

Facial recess –
• Triangular area inferior to the incudal fossa.
• Lateral to facial nerve vertical segment.
• Medial to chorda tympani nerve.
• Used in intact canal wall mastoidectomy to gain access to ME.
Nervus intermedius (nerve of wrisberg) –
• Carries taste, secretory & sensory fibres of facial nerve.
• Runs separate in IAC
• Occupies dorsal aspect in tympanic segment & posterolateral aspect in
mastoid segment.

Cochlear nerve –
• Arise from spiral ganglion neurons.
• At the fundus, it is in anteroinferior compartment.
• Rotates as it heads towards porus
• Enters brainstem a few mm caudal to root entry
zone of V nerve.
Vestibular nerves –
• SVN & IVN occupy posterior half of IAC.
• SVN innervates superior & lateral scc, utricular
macula, superior saccular macula.
• IVN innervates inferior saccular macula
• Posterior ampullary br of IVN, separates a few mm
away from porus, traverses singular canal to
posterior canal ampulla and supplies post scc.

Sensory nerves of tympanomastoid compartment –
• Jacobson’s nerve (tympanic br of IX nerve) -
• Arises from petrosal ganglion located in petrosal fossa of jugulocarotid crest
• Through inferior tympanic canaliculus, enters ME along with inf tymp art
• Then it climbs the promontory to meet caroticotympanic plexus.
• Lesser petrosal nerve is formed here by joining of pregaanglionic
parasympathetic jacobson fibres with postganglionic sympathetic
caroticotympanic plexus.
• LPN heads to floor of MCF within or parallel to semicanal of tensor tympani.
• Jacobson’s nerve mediates otalgia from pharynx.

• Arnold’s nerve (auricular br of X nerve)-
• It has fibres from VII, IX & X nerves.
• Originates in jugular foramen
• Passes over dome of jugular bulb (via mastoid canaliculus)
• Enters fallopian canal
• It has been implicated in herpetic involvement of the EAC in herpes zoster
oticus and the cough reflex elicited by manipulation of EAC.

VASCULAR ANATOMY
Temporal bone arteries –
• ICA :-
• Enters temporal bone through external
carotid foramen located anteromedial to
styloid process.
• Course in intrapetrous segment –
• 1st passes anterior to tympanic cavity &
cochlea
• Then bends (it’s knee) to run medial to ET &
inferomedial to semicanal of TT muscle
• Then it climbs to exit the temporal bone at
internal carotid foramen.
• Venous & sympathetic plexus accompanies it
throughout intrapetrous course.
• Bony shell covering it is very thin (<0.5mm)
and dehiscent in 6% cases.
• In ME surgeries, medial wall of ET gently
dissected not to injure ICA.

VASCULAR ANATOMY cont….
• Anterior Inferior Cerebellar Artery –
• AICA often extends a loop into the IAC.
• This may cause symptoms like vertigo & tinnitus.
• Disruption of AICA causes haemorrhage in and infarction of the labyrinth &
brainstem.
Temporal bone veins –
• 3 dominant sinuses are sigmoid, superior
petrosal & inferior petrosal.
• Sigmoid is a portion of lat venous sinus.

• Sup sagittal & straight sinuses
merge at the internal occipital
protuberance.
• Right and left transverse sinuses
extend beyond this junction & lie
inferior to the tentorium.
• Anteriorly, sup petrosal sinus joins
the transverse sinus and this
junction marks the beginning of
sigmoid sinus.

• Lateral venous sinus
• occupies an S-shaped sulcus in posterior mastoid extending from transverse
sinus to internal jugular vein.
• Angle of citelli – angle between sigmoid sinus/
PCF dura and the MCF dura.
• Superior petrosal sinus
• drains cavernous into lateral venous.
• Runs in sup petrosal sulcus at junction of
PCF & MCF dural plates.
• Inferior petrosal sinus
• Courses in petro-occipital suture line.
• Drains cavernous into jugular bulb.

• Emissary veins are drainage routes of the dural venous sinuses
through the skull that communicate with the superficial veins of the
scalp.
• A fairly constant emissary vein, the mastoid emissary vein, can be
found at the junction of the temporal and occipital bones and usually
communicates with the occipital or postauricular vein.
Greisinger’s sign –
• Tenderness and edema over the mastoid are
pathognomonic for suppurative thrombo-
phlebitis of the sigmoid sinus and reflect
thrombosis of mastoid emissary vein.

Classification-of-the-Superior-Petrosal-Veins-and-Sinus-Based-on-Drainage-Pattern

• Arachnoid granulations (pacchionian bodies) –
• projections of pia-arachnoid into the venous sinuses & venous lacunae
• are extensions of subarachnoid space.
• also extend from arachnoid of MCF & PCF into adjacent mastoid air cells.
• Gacek linked adult onset spontaneous CSF leak to these granulations.
• Jugular bulb –
• Between sigmoid sinus & internal jugular vein
• Has a thin wall that does not contract with bipolar & is prone to rupture
• High-riding (extending above the level of inferior tympanic annulus) jugular
bulbs have a very thin wall (0.1-0.3mm). It encroaches <2mm inferior to IAC. It
may mimic ME vascular mass like glomus tympanicum

Middle ear blood vessels –
• Inferior tympanic artery
• Br of ascending pharyngeal (br of ECA)
• Traverses inferior tympanic canaliculus with jacobson nerve.
• Feeder of tympanic paragangliomas
• Anastomotic network of tympanum –
• Formed by br of ECA like ant tympanic, deep auricular, mastoid, stylomastoid,
superficial petrosal & tubal……

Labyrinthine vessels –
• Labyrinthine artery
• Br of AICA
• Subarcuate artery
• Br of labyrinthine or AICA or both
• Passes within arch of sup scc.

Facial nerve vessels –
• Intrinsic system
• Runs within the nerve
• Poorly developed in labyrinthine segment
• Well developed in tympanic & mastoid segments
• Extrinsic system
• AICA supplies intracranial segment
• Superficial petrosal supplies GG & superior mastoid segment
• Stylomastoid artery supplies inferior mastoid segment

Anatomy temporal bone

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