HRCT temporal bone

1. HRCT Temporal bone anatomy

2. Planes of scanning
 Axial
 30 Degrees to anthropological base line
 Parallel to lateral SCC.
 Best displays inner & middle ear.
 Sections parallel to the hard Palate
 Direct Coronal plane
 patient head extended in prone or supine with 105 degree
 plane is perpendicular to the lateral SCC
 Sections are parallel to posterior wall of maxillary sinus
 Saggital plane
2
105
0
30

3. Temporal Bone
1.Squamous
2.Petrous
3.Mastoid
4.Tympanic
5. Styloid
3
Lateral wall of MCF
Mastoid air cells
Encloses Labyrinth
Forms bony EAC
Forms Styloid process

5. EAR IS DIVIDED INTO 3 PARTS
• EXTERNAL EAR
• MIDDLE EAR
• INTERNAL EAR
5
EAC
Tympanic cavity
Bony & membranous labyrinth

6. 6
EXTERNAL EAR
External auditary canal-
2.5 cms in length
Cartilaginous
Lateral 1/3rd
Osseous
Medial 2/3rd
Tympanic membrane-makes 55 degree angle
With floor of the meatus

7. 7
Boundaries & Communications Of Middle Ear
Roof- Tegmen tympani
Separates from MCF
Floor-thin convex bone
separating from superior bulb of IJV
Lateral wall-tympanic membrane
Medial wall – separates from inner ear
Anteriorly -auditory tube
Posteriorly –mastoid antrum

8. 8
1)PROMOTARY- Round bulge produced by basal turn of cochlea
2)FENESTRA OVALIS -Lies postero- superior to promontory & connects
middle ear with vestibule and is occupied by footplate of stapes
3)FENESTRA ROTUNDA- Posteroinferiorly to oval window & connects ME
with scala tympani of cochlea.
4)PROMINENCE OF FACIAL NERVE CANAL -Runs backwards just above the
oval window to reach the lower margin of aditus.
Medial wall of middle ear:

9. 9
ANTERIOR WALL
1) Superior-opening of
canal for tensor tympani.
2) Middle –opening of
auditory tube.
3) Inferior-thin plate of
bone separating from
carotid canal.
POSTERIOR WALL
1) Aditus to mastoid
2) Fossa incudis-lodges the short process of incus.
3) Pyramidal eminence-attachment for stapedial tendon.

10. • The scutum is normally thin and sharply edged;
and is an important bony landmark as it is one of
the bony structures eroded early by a
cholesteatoma.
•
• Scutum, the tympanic membrane and the tympanic
annulus are best demonstrated on coronal images
at the mid bony portion of the external auditory
canal.

12. Middle Ear
• three compartments in
coronal plane.
• A line drawn from lower
edge of the scutum to the
tympanic portion of the
facial nerve -
epi/mesotympanum.
• parallel to the floor of the
external auditory canal
meso/hypotympanum

13. Epitympanum
It contains :
• Head of the malleus
• Malleo–incudal
articulation
• Body and short
process of the incus,
• Short process of Incus
projects posteriorly
towards aditus.
These structures are
best demonstrated on
axial images.

14. • Tegment tympani –
roof of
epitympanum –
barrier between
middle cranial fossa
and middle ear
cavity.
• Best evaluated on
coronal images

15. • Posteriorly the
epitympanum opens
into the mastoid
antrum via the aditus
ad antrum;
demonstrated on
both the axial and
coronal images

16. Mesotympanum
• The mesotympanum
contains the ossicular
chain
• Oval and round
window
• Long process of the
Incus
• Stapes
• Handle of Malleus
• Facial nerve Canal

17. • The ice-cream cone sign represents the
normal appearance of the malleus and incus
on an axial high-resolution CT scan (HRCT)
image of the temporal bone .
• The ball (scoop) of the ice cream is formed by
the head of malleus and the cone is formed by
the body of the incus.
• The space between the ice-cream cone and
the scutum is called Prussak's space.

19. • On coronal images
the long process of
incus is vertically
oriented parallel to
the long process of
malleus,
continuing as the
rounded lenticular
and the facet to
articulate with the
head of the stapes

20. • The stapes hub and
crura are best
demonstrated on
axial images at the
level of the oval
window
• The stapes
footplate sits in the
oval window niche
and cannot always
be discretely
identified on CT.

21. MALLEUS
• Epitympanum:
Headarticulates
with body
of Incus( Ice
Cream Cone )
• Mesotympanum
: Neck andHandle.

22. INCUS
Mesotympanum: Longprocess
(LPI) articulates with head of
Stapes.
Epitympanum: Short process is
the most posterior part and
points towards aditus.

23. Stapes
The stapes is the smallest
bone in the body.
Head ,neck, crura (anterior
and posterior) and a
footplate.
St T- Stapedius tendon

24. Axial Section at Mesotympanum
• Two parallel
structures
• Anteriorly: Neck and
Handle ofMalleus(H)
• Posteriorly: Long
process ofIncus (LPI)

25. • Anteriorly: Head
andhandle of
Malleus
• Posteriorly: Long
processof Incus (LPI)
Coronal section Mesotympanum

26. At the posterior wall of the
mesotympanum
• bony protuberance -
pyramidal eminence-
stapedius muscle exits to its
attachment at the neck of the
stapes
• Lateral to it - facial recess
for descending (mastoid)
segment of the facial nerve
• Medial to it - sinus tympani
- a blind spot for the
surgeon during transmastoid
surgery and so
cholesteatoma at this site
may be overlooked

27. Medial Wall
• Promontory - a bony
prominence on the
medial wall of the
mesotympanum -
protrusion of the
basal turn of the
cochlea.
• Above the
promontory is the
oval window and
posteroinferior to
which is the round
window niche

28. Anterior wall
•
The anterior wall has a thin
plate of bone which
separates this portion from
the internal carotid artery
as it enters the skull.
• Always look for bone
covering ICA.
• 2 openings in anterior wall
• Upper : canal for tensor
tympani (Stt)
• Lower : Eustachian tube (Et)
• Axial section is best for
Eustachian tube, semi canal
and carotidcanal.

30. 30
Inner ear- Osseous & Membranous
Osseous- vestibule
Semicircular canals
Cochlea

32. • Cochlea
• The perilymphatic space of
vestibule is continuous with
the cochlea anteriorly.
• The cochlea is a conical
structure,extends for 2.5-
2.75turns
• Promontory
(P) is the projection raised by
the basal turn of cochlea.
• The basal turn opens into the
round window niche
Coronal
Middle
turn
Axial

33. • The vestibule
consists of the
superior utricle and
the inferior saccule.
• The semicircular
ducts open into the
utricle.

35. Axial coronal
• SSC
PS
PSC
SSC

37. • The cochlear aqueduct
contains the
perilymphatic duct
while the vestibular
aqueduct contains the
endolymphatic duct
and the intraosseous
portion of the
endolymphatic sac.

38. • The internal auditory canal shows considerable
individual variation in size and configuration but
should be symmetrical in any one person
• The medial opening - porus acousticus.
• Divided at its most lateral end by the horizontal
crista falciformis and vertical crests into four
compartments.
• The facial nerve is in the anterosuperior
compartment, the cochlear nerve is in the
anteroinferior compartment while the superior and
inferior vestibular nerves are in posterior superior
& inferior compartments,

41. Facial Nerve
• VII n:-
– Intracranial segment
– Labyrinthine segment
– Tympanic segment
– Mastoid portion
– Parotid segment
41

42. • The facial nerve, from the lateral end of the
internal auditory canal enters the petrous bone as
the labyrinthine portion running anterolaterally,
superior to the cochlea and towards the anterior
genu (geniculate ganglion).
• Then it makes an abrupt turn to run
posterolaterally along the medial attic wall
beneath the lateral semicircular canal as the
tympanic portion towards the posterior genu.
• And finally turns inferiorly as the descending
(mastoid) portion to exit at the stylomastoid
foramen.

43. How to identify Facial nerve canal?
• Axial: at level of
Epitympanum, it is seen as a
linear structure medial to
ice-cream cone.
• Coronal: At level of OW, it is
seen as a round structure
with bony outline between
OW inferiorly and Lateral
Semicircular canal
(LSC)superiorly.
Coronal: A

45. Sigmoid plate -thin bone separating the sigmoid
sinus from adjacent structures (especially mastoid air
cells).

46. 46
Axial sections-caudal to cephalad
1.Axial hypotympanic-jugular foramen level
1)carotid canal & jugular
Fossa forming snowman
Configuration
2)opening of auditary
Tube
3)petrooccipital fissure
4)TM joint and mandibular
Condyle

47. 47
Carotid canal
Jugular fossa
Auditory tube
Temporo
mandibular jt
Petro
occipital fissure

48. 48
2.Axial inferior tympanic
level
1)ant &post walls of EAC
2)descending facial nerve canal
3)carotid canal
4)cochlear aqueduct
5)long process of
Malleus.

49. 49
Descending
facial nerve
Cochlear
aqueduct
EAC
Promontory
canal
For
tensor
tympani

50. 50
3.Axial mid tympanic level
1)neck of malleus ,long process of
incus and stapes
2)semicanal for tensor
tympani
3) 3 turns of cochlea
4)facial nerve canal

51. 51
malleus
incus
stapes
Round window

52. 52
Oval window
IAC
Scala tympani
Facial recess

53. 4. Axial Epitympanic
IAC level
• Ice-cream cone appearance-head of
malleus and body of incus
• Stapes –occasionally seen articulating
with oval window.
• Internal auditory canal
• Descending facial nerve canal
53

54. 54
Ice cream cone
appearance
Facial nerve
canal
Internal auditory
canal

55. 5. Axial lateral semicircular canal level
• 1)mastoid antrum and its aditus
& Koerner’s septum
• 2) lateral semicircular canal and
vestibule
• 3) post semicircular canal
&vestibular aqueduct
• 4) IAC
• 5) sq part of temporal bone.
• 6) geniculate ganglion
55

56. 56
LATERAL SC CANAL
VESTIBULE IAC
PROXIMAL LIMB OF
7TH N
ADITUS TO MASTOID
ANTRM
VESTIBULAR AQUEDUCT

57. 57
CORONAL SECTIONS
1. Coronal anterior tympanic level
-Head of malleus
-Tegmen tympani
-Basal & 2nd turn of
Cochlea
-Geniculate ganglion
- scutum

58. 58
COCHLEA
IAC
HEAD OF MALLEUS
SCUTUM
GENICULATE GANGLIA
SQ TEMP
ORAL
BONE

59. 59
2.Coronal mid-tympanic level
-L shaped incudo-stapedial articulation
-Stapes
-Oval window
-Tegmen tympani

60. 60
IAC
Oval Window
Incus in aditus
Stapes
Tegmen tympani

61. 61
3.CORONAL OVAL WINDOW LEVEL
•IAC
•Oval window
•Stapes
•Lateral SCC

62. 62
Vestibule
IAC
Sup SCC
Antrum
Lateral SCC
Oval window
Middle ear
EAC

63. 63
5.Coronal jugular foramen
level
•Jugular foramen
•Descending facial
Nerve
•Mastoid antrum
•Occipital bone and atlas

64. 64
Jugular fossa
Descending facial nerve
Mastoid Air Cells

65. Role of MRI
• Excellent in studying Inner ear
– Membranous labyrinth
– Vestibule
– Saccule & utricles
• Preoperative evaluation in pts for Cochlear implants
• To evaluate CP angle tumors
• To evaluate Neurovascular bundles
• Functional assessment – Nerve stimulation
• Virtual scopy
65

66. 66
7 & 8th nerve complex
Cochlea