temporal bone anatomy imaging temporal bone radiology temporal bone hrct temporal bone H.R.C.T TEMPORAL BONE middle ear cochlea semicircular canal

1. z
ANATOMY OF
TEMPORAL
BONE
DR. KANIKA BHARGAVA
P.G. RESIDENT 2ND YEAR

2. z  The temporal bone is situated on the sides and the base of the
cranium and lateral to the temporal lobe of the cerebrum. The
temporal bone is one of the most important calvarial and skull base
bones. The temporal bone is very complex and consists of five
parts:
 squamous part
 mastoid part
 petrous part
 tympanic part
 styloid process (or part)
 Some anatomists describe only 4 parts of the temporal bone, with
the mastoid and petrous parts combined as a petromastoid part 3.

4. z
 The Squama (squama temporalis)- The squama forms the upper
and anterior part of the bone, and is scale-like thin and
translucent.
 Mastoid portion(pars mastoidea)- The mastoid portion forms the
posterior portion of the bone.
 Petrous portion( pars petrosa)- is pyramidal in shape and is
wedged in at the base of the skull between thee sphenoid and
occipital bone. Directed medialward, forward and a little upward.
 Tympanic part(pars tympanica)- the tympanic part is a curved
plate lying below the squama and in front of the mastoid
process.
 Styloid process(processus styloideus)- it is slender, pointed, and
of varying length ; it projects downward and forward, from under
the surface of temporal bone.

6. z
ANATOMY OF EAR
 EXTERNAL EAR
 MIDDLE EAR
 INTERNAL EAR (LABYRINTH)

7. z
EXTERNAL EAR
External ear comprises of the:
 The auricle(or pinna)
 The external auditory meatus
 Tympanic membrane( eardrum)

8. z
AURICLE (PINNA)
 The auricle is the part of the
ear that projects laterally from
the head.
 It is composed of an irregular
concave plate of elastic
cartilage and dense
connective tissue, covered by
skin which contains short hairs
(tragi), sebaceous glands, and
ceruminous glands.

9. z
EXTERNAL AUDITARY CANAL
 The external auditory canal (EAC) or external auditory meatus
(EAM) extends from the lateral porus acusticus externus medially to
the tympanic membrane.
 The EAC is typically 2.5 cm in length and is S-shaped.
 The lateral 1.5 cm are bounded by a fibrocartilaginous tube
continuous with the auricle.
 The medial 1 cm is formed by the bony margins of the temporal
bone (the squamous part superiorly and the mastoid part
posteriorly).
 The skin of this inner part is directly applied to periosteum, with no
subcutaneous tissue present.

10. z
Boundaries
 medially
 superior: scutum
 middle: tympanic membrane
 inferior: tympanic annulus
 laterally: external auditory
meatus surrounded by the
pinna (auricle)

12. z
RELATIONS
 anteriorly: temporomandibular joint
 posteriorly: mastoid air cells
 superiorly: superolateral mastoid air cells
 inferiorly: parotid space

13. z
TYMPANIC MEMBRANE
 The tympanic membrane is a thin membrane that separates
the external ear from the middle ear. It acts to transmit sound
waves from air in the external auditory canal (EAC) to the
ossicles of the middle ear.
 Gross anatomy:
 The tympanic membrane is shaped like a flat cone pointing into
the middle and inner ear. At the center of the concavity the
deepest point is called the umbo.
 It attaches to an incomplete ring of bone along the wall of the
EAC, the tympanic annulus. It consists of three layers (from
external to internal):
 cutaneum (skin)
 radiatum circulare (collagen fibres)
 mucosum (epithelium)

14. z
 There are two distinct portions of the membrane:
 pars tensa: the tense portion of the membrane is the larger portion and
extends from the anterior and posterior malleolar folds at the level of the
lateral process of the malleus to the inferior edge of the membrane
 pars flaccida: the flaccid portion of the membrane is much smaller and is the
portion of the membrane above the anterior and posterior malleolar folds
 Quadrant separation
 It is anatomically separated into four quadrants:
 anterosuperior
 anteroinferior
 posteroinferior
 posterosuperior

15. z This is important because
vessels and nerves
(specifically chorda
tympani nerve) pass
through the superior
portion of the membrane.
Additionally, the light
reflex (cone of light) is
specific to the
anteroinferior portion of
the membrane. Thus,
when intervention is
performed, the
posteroinferior portion of
the membrane is chosen.

17. z
MIDDLE EAR
 The middle ear (a.k.a. tympanic cavity or
tympanum) is an air-filled chamber in the petrous
part of the temporal bone.
 It is separated from the external ear by the
tympanic membrane, and from the inner ear by
the medial wall of the tympanic cavity.
 It contains the three auditory ossicles whose
purpose is to transmit sound vibrations from the
tympanic membrane to the lateral wall of the inner
ear.

18. z
 The tympanic cavity is further subdivided into
three parts:
 the mesotympanum (the space directly medial
to the tympanic membrane),
 superiorly the epitympanum or attic (the space
superior to the membrane),
 and inferiorly, the hypotympanum, a shallow
trough below the level of the membrane, from
which the Eustachian tube arises 4.
 Some texts divide the middle ear into two
compartments only: the tympanic cavity proper
and the epitympanic recess.

19. z
Tympanic cavity
 The tympanic cavity is the major portion of
the middle ear and contains the ossicles of
the middle ear.
 Medial wall
contains the oval and round window and the
prominence of the tympanic segment of the
facial nerve.
 Lateral wall
is mainly formed by the tympanic membrane.
The scutum is the bony prominence at the
upper part or pars flaccidum of the tympanic
membrane.
 Roof
is called the tegmen and separates the upper
part of the tympanic cavity or epitympanum
from the middle cranial fossa.
 Posterior wall
forms the entrance to the mastoid and is
called the aditus ad antrum.

22. z
 5. The mastoid (posterior) wall: This
features the aditus (opening) to the
mastoid antrum in its superior part,
which connects the tympanic cavity to
the mastoid cells.

23. 6. The carotid (anterior) wall: This
separates the tympanic
membrane from the carotid canal.
In its superior aspect there is an
opening of the Eustachian tube
(also known as the
pharyngotympanic tube) and the
canal for the tensor tympani

24. z
Contents
 Bones
 Middle ear ossicles consist of three small bones
(the malleus, incus and stapes), which form a
mobile chain across the tympanic cavity from
the tympanic membrane to the oval window.
 Muscles
 There are two muscles, one for the malleus and
one for the stapes, which act to damp down
over-vibration from low-pitched sound waves.
These are, respectively:
 tensor tympani
 stapedius

25. z
Nerves
The chorda tympani
leaves the facial nerve
in the facial canal and
enters the tympanic
cavity through the
posterior wall, lateral to
the pyramid, lying just
underneath the mucous
membrane. It runs over
the pars flaccida of the
tympanic membrane,
and the neck of the
malleus. It leaves at the
anterior margin of the
tympanic notch.

30. z
FACIAL NERVE
 The facial nerve has six named segments :
 intracranial (cisternal) segment - zero branches
 meatal (canalicular) segment (internal auditory canal): 8 mm long, zero
branches
 labyrinthine segment (IAC to geniculate ganglion): 3-4 mm long, 3
branches (from geniculate ganglion)
 tympanic segment (from geniculate ganglion to pyramidal eminence): 8-
11 mm long, zero branches
 mastoid segment (from pyramidal eminence to stylomastoid
foramen): 8-14 mm long, 3 branches
 extratemporal segment (from stylomastoid foramen to division into
major branches): 15-20 mm, 9 branches

31. z
Labyrinthine segment of facial nerve
 The labyrinthine segment of the
facial nerve coming from the
internal auditory canal angles
sharply forward, nearly at right
angles to the long axis of the
petrous bone, to reach the
geniculate ganglion.
 At the ganglion the facial nerve
makes a U-turn (first genu of the
facial nerve) to run posteriorly as
the tympanic segment along the
medial wall of the epitympanum.

34. z
INTERNAL AUDITARY CANAL
 The internal acoustic canal (IAC), also known as the internal auditory
canal or meatus (IAM), is a bony canal within the petrous portion of the
temporal bone that transmits nerves and vessels from within the posterior
cranial fossa to the auditory and vestibular apparatus.
 Gross anatomy
 The opening of the IAM, the porus acusticus internus, is located within the
cranial cavity, near the posterior surface of the temporal bone. The margins
of the opening are smooth and rounded, and the canal is short (1 cm),
running laterally to the bone. The canal narrows laterally, and the lateral
boundary is the fundus, where the canal splits into three distinct openings,
one of which is the facial canal.

35. z
 Contents
 facial nerve
 vestibulocochlear nerve
 vestibular ganglion
 labyrinthine artery (usually a
branch of the AICA or basilar
artery)

37. z

38. z
 The inner ear refers to the bony labyrinth, the membranous
labyrinth and their contents. It is divided into three main parts:
 cochlea
 vestibule
 semicircular canals

39. z
COCHLEA
 The cochlea is part of the inner ear osseous
labyrinth found in the petrous temporal bone.
 Gross anatomy
 The cochlea is a shell-shaped spiral that
turns between two-and-a-half and two-and-
three-quarters times around the modiolus (a
central column of porous bone).
 The spiral of the cochlea is separated by the
osseous spiral lamina and consists of the
scala tympani (lower portion), scala media
and scala vestibuli (upper portion).
 The scala tympani and scala vestibuli are
filled with perilymph and the scala media by
endolymph.

40. z The organ of Corti, a strip of sensory
epithelium located in the scala media,
lines the spiral of the cochlea.
 The round window is an opening
(covering by a membrane) in the middle
ear that communicates with the cochlea
and enables movement of cochlear
lymph.
 Communications
 cochlear aperture: opening of the distal
internal acoustic canal that transmits the
cochlear nerve
 with the vestibule posterosuperiorly

44. z
VESTIBULE
 The vestibule is an approximately 4 mm
central chamber of the bony labyrinth. It is
dominated by depressions housing the:
 utricle (elliptical recess)
 saccule (spherical recess)
 basal end of the cochlear duct (cochlear
recess)
 The cribrose areas have perforations through
which the nerve bundles gain access to the
inner ear.
 The endolymphatic duct is housed within the
bony vestibular aqueduct and originates at the
posteroinferior aspect of the vestibule.

47. z
SEMICIRCULAR CANAL
 The semicircular canals are components of the bony
labyrinth along with the cochlea and vestibule.
 Gross anatomy
 There are three semicircular canals on each side:
 superior semicircular canal: vertical plane
 posterior semicircular canal: vertical plane
 lateral semicircular canal: 30 degrees to the horizontal
 The semicircular canals are interconnected tubes, each
forms two-thirds of a circle and located in three planes
perpendicular (at right angles) to each other.
 The arcuate eminence, which is located at the anterior
surface of the petrous temporal bone (PTB), indicates the
location of the superior semicircular canal.