The CT-scanof the temporal bone is an exam of utmost importance for both the diagnosis of several diseases and the planning of a safe otologic surgery.

1. HOW TO READ CT SCAN
TEMPORAL BONE??
PROTOCOL OF DHULIKHEL
HOSPITAL
Prof. Dr. Bikash Lal Shrestha
Department of ENT-HNS
Dhulikhel Hospital
Kathmandu University Hospital
Kavre, Nepal
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2. Why it is necessary??
 To identify the anatomy.
 For the surgical planning.
 To assess the risk.
 Informed consent.
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3. 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
30 degree
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4. 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
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5. ELEVEN ITEMS CHECK LIST
OF CT SCAN TEMPORAL BONE
 Pneumatisation and ventilation.
 Jugular bulb.
 Carotid artery.
 Eustachian tube.
 Ossicles.
 Cochlea.
 Semicircular canals.
 Facial nerve.
 Sinus Plate.
 Dural Plate
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6. AXIAL IMAGES
 Pneumatisation and ventilation of the
mastoid (including the petrous apex) and
middle ear.
 Evaluate the external and middle ear by
following : external auditory canal,
tympanic membrane, ossicular chain
(malleus, incus, stapes), oval and round
window.
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7.  Evaluate the inner ear from
superiorly to inferiorly: semicircular
canals, vestibule and vestibular
aqueduct, cochlea and cochlear
aqueduct.
 Evaluate facial nerve canal, carotid
canal, jugular bulb, and sigmoid sinus
plate.
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8. PNEUMATISATION
AND VENTILATION
OF MASTOID AIR
CELLS
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9. Well pneumatized and ventilated mastoid on right side
Poorly pneumatized mastoid air cells on right side
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10. Well pneumatized and poorly
ventilated mastoid air cells
on right side
Well pneumatized and well
ventilated mastoid air cells on left
side
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11. EXTERNAL AUDITORY
CANAL AND
TYMPANIC MEMBRANE
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12. External auditory canal anterior wall
External auditory canal posterior wall
Tympanic membrane
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13. OSSICULAR CHAIN
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14. Ossicular
Chain:
Malleus head
as ball of ice
cream and
incus body and
short process
as cone of ice
cream
Malleus head
Incus body and short process
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15. Stapes
crura:
Looks
like arc
shaped.
Stapes anterior crura
Stapes posterior crura
Lenticular process
of incus
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16. Oval window and Round
window
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17. Oval window:
• Lies just adjacent
to the cochlea
• Stapes footplate
lies on the oval
window.
Oval window
Stapes footplate and crura
Basal turn of cochlea
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18. Round
window:
Lies inferior to
promontory.
Covered by round
window niche.
Promontory
Round window
niche
Round window membrane
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19. INNER EAR
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20. SUPERIOR SEMICIRCULAR
CANAL
 CT scan reading should be
performed from superior to inferior
direction.
 First structure appear which lies
perpendicular to long axis of
temporal bone – Superior
semicircular canal.
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21. Long axis of temporal bone
Superior
semicircular
canal –
perpendicular
to long axis
2 limbs of superior semicircular canal
Cobra eye appearance
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22. POSTERIOR SEMICIRCULAR
CANAL
 It lies parallel to the long axis of
temporal bone.
 On scrolling, it is seen below
Superior semicircular canal.
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23. Posterior
semicircular
canal lies
parallel to long
axis of temporal
bone
Long axis of temporal bone
Crus commune
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24. LATERAL SEMICIRCULAR
CANAL AND VESTIBULE
 It looks signet ring appearance.
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25. Lateral
semicircular
canal
Vestibule
Signet
ring
appearanc
e
Lateral semicircular canal
Vestibule
Posterior semicircular canal
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26. VESTIBULAR AQUEDUCT
Vestibular aqueduct
Posterior semicircular canal
“Vestibular
aqueduct lies
parallel and
posterior to the
posterior
semicircular canal”
It houses the
endolymphatic duct
and sac.
Parallel
and
posterior
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27. COCHLEA
Stack of coins appearance
Basal turn
Mid turn
Apical turn
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28. Carotid artery lie just anteroinfero and
medial to the basal turn of cochlea
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29. COCHLEAR AQUEDUCT
Cochlear aqueduct :
Lies inferiorly at the
level of promontory. It
looks like internal
auditory canal as shown
in right sided scan.
Internal
auditory canal
: lies
superiorly at
the level of
lateral canal.
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30. CAROTID ARTERY, JUGULAR
BULB AND SIGMOID SINUS
Jugular bulb
Carotid artery – vertical segment
Sigmoid sinus plate
Horizontal
segment of
carotid
artery lying
at the level
of sphenoid
sinus
Sphenoid sinus
Mastoid
emissary
vein
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31. FACIAL NERVE
 In axial cut from superior to
inferior, the different segments of
facial nerve can be identified.
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32. Meatal segment of facial nerve
within internal auditory meatus
Meatal foramen
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33. Labyrinthine segment of
facial nerve
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34. First genu
Tympanic
segment of
facial nerve
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35. Tympanic segment of facial nerve
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36. Vertical/mastoid segment of facial nerve
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37. Vertical/mastoid segment of facial nerve
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38. CORONAL IMAGE
 Check for the scutum/tegmen
tympani (dural plate), and the bone
covering the lateral semicircular
canal.
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39.  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.
Epitympanum
Hypotympanum
Mesotympanu
m
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40. SCUTUM/TEGMEN
TYMPANI/DURAL PLATE
 Tegmen tympani – roof of epitympanum – barrier
between middle cranial fossa and middle ear
cavity.
Tegmen tympani (showing intact dural plate)
Scutum
Head of malleus
and body of
incus
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41. In Coronal image, the
mesotympanum contains:
 The ossicular chain (Long and lenticular process of the
Incus, stapes, handle of Malleus)
 Oval and round window
 Facial nerve Canal
Long process of incus
Lenticular
process of
incus
Stapes and oval
window area
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42. Fallopian canal lying
just inferior to lateral
canal
Lateral semicircular canal
Round window
Oval window
Superior semicircular canal
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43. Mastoid segment of facial
nerve in coronal cut
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44. Surgically Important Spaces
within the temporal bone
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45. Cog
Prussak’s space
Fossa incudis
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Prussak's space

47. Sinus tympani
Facial recess
Pyramid
Vertical segment
of facial nerve
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48. EUSTACHIAN TUBE
Opening of the Eustachian
tube – completely aerated
and patent
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49. THANK YOU
FOR
WATCHING.
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