The document provides an overview of the normal anatomy of the petrous bone, middle ear, and inner ear as seen on radiological imaging. It describes the structures that form the walls and boundaries of the middle ear space, including the tegmen tympani, jugular bulb, and carotid artery. Key structures of the inner ear like the cochlea, vestibule, semicircular canals, and internal auditory canal are also outlined. Various radiographic views used to examine the temporal bone and mastoid air cells are listed. Axial, coronal, and sagittal cross-sections through the temporal bone demonstrate the spatial relationships between the middle ear, inner ear, and surrounding structures.

1. Dr/ ABD ALLAH NAZEER. MD.
Radiological anatomy of the petrous bone.

2. Normal Anatomy of the Middle Ear
The temporal bone houses and is surrounded by many vital structures.
The temporal bone is actually composed of four bones, consisting of the
squamous, petrous, tympanic, and mastoid segments.
The bony framework of the temporal bone contains multiple air spaces.
The most complex of these spaces is the middle ear cavity, or tympanum.
The middle ear space is shaped somewhat in the form of a red blood cell
stood on end. This space is narrow in a medial-lateral direction and more
elongated anteroposteriorly and superoinferiorly.
Laterally, the tympanic membrane, annulus, and the handle of the malleus
make up the wall of the tympanum. The inner ear forms the medial wall of
the middle ear. The largest anatomic structure of the medial wall is the
promontory of the cochlea.
The roof of the middle ear space is formed by the tegmen tympani. This
structure separates the middle ear space from the middle cranial fossa.
The tegmen slopes inferiorly as it courses laterally along the temporal
bone; remember this point during mastoidectomy to avoid violating the
tegmen with the drill. In addition, the tegmen is located higher than the
superior border of the tympanic membrane, forming a space, the
epitympanum. The epitympanum houses the head of the malleus and the
body and short process of the incus.

3. The floor of the middle ear is primarily composed of the bone covering the
jugular bulb. The bone over the bulb may be dehiscent, rendering it more
susceptible to injury. The floor of the middle ear cavity is located further
inferiorly than the lowest extent of the tympanic membrane, creating a
space, the hypotympanum.
Anteriorly and inferiorly, the carotid artery limits the tympanum. More
superiorly, the eustachian tube, tensor tympani, and cochleariform
process can be observed along the anterior margin of the middle ear.
The mastoid air cells lie immediately posterior to the middle ear space.
The entrance to the mastoid air cells is the aditus ad antrum. The
pyramidal eminence (giving rise to the stapedius tendon) and the incudal
fossa can also be observed immediately posterior to the middle ear space.
The middle ear space contains several spaces of clinical significance. The
sinus tympani is located between the labyrinthine wall and the pyramidal
eminence. This area is a common site for recurrence of cholesteatoma.
The facial recess is found between the tympanic annulus and pyramidal
eminence. This recess provides improved access to the middle ear space
during a tympanomastoidectomy.

4. Normal Anatomy of the Inner Ear
The inner ear is housed in the bony labyrinth, which is well
demonstrated on CT scans. The cochlea lies anteriorly. The cochlea is
a conical structure, with its apex pointed anteriorly, inferiorly, and
laterally; its base rests near the internal auditory canal and extends
outward for 2.5-2.75 turns. Immediately anterior to the cochlea is
the carotid artery. The round window is located in the scala tympani
of the basal turn of the cochlea. The round window niche houses the
round window. This window is the termination of the scala tympani
of the cochlea. The niche protects the round window from direct
exposure to sound waves in the event of a tympanic membrane
perforation.
The vestibule lies posterior to the cochlea, abutting the internal
auditory canal medially. The stapes footplate transmits vibrations to
the vestibule at the oval window. The 3 semicircular canals emanate
from the vestibule. The lateral canal lies 30° from horizontal. The 3
canals lie at right angles to each other.

5. The endolymphatic sac is posteromedial to the semicircular
canals on the posterior margin of the petrous bone. The
seventh and eighth cranial nerves (CN VII and CN VIII) course
through the internal auditory canal. CN VIII enters the
structures of the inner ear to innervate them and CN VII passes
laterally and anteriorly to the geniculate ganglion, then
posteriorly along the medial wall of the tympanum before
heading inferiorly to the stylomastoid foramen.
A retrospective CT-scan study by Saxby et al found the rate of
semicircular canal dehiscence in pediatric patients to be
significantly lower than rates found in previous studies. The
study involved 334 children (649 temporal bones), with
temporal bone imaging revealing superior canal dehiscence in
3.3% of patients (1.7% of temporal bones) and posterior canal
dehiscence in 2.1% of patients (1.2% of temporal bones).

6. Radiographic positions of mastoids
The mastoid process is a part of the temporal bone which is also comprised of tympanic,
petrous and squamous parts. Accordingly, examination of the mastoid can be possible
using the following projections:
Law view: The X-ray beam is directed at a 15 degree oblique plain cephalocaudally while
the skull's sagittal plane is parallel to the X-ray film.
Law view: The X-ray beam is directed at a 15 degree oblique plain
cephalocaudally while the skull's sagittal plane is parallel to the X-ray film.

7. Stenver's view: It is also called an Axio-anterior oblique posterior view. The X-ray
beam is directed at a 14 degree angle caudally and the head faces the film with
slight flexion and rotation at an angle of 45 degrees to the opposite side.

8. Transorbital view: (posterioanterior and anteroposterior): The X-ray
beam is directed either postero anteriorly or anteroposteriorly along
the orbito-meatal line at a 90 degree angle to the film.

9. Town's view: It is an anteroposterior view with a 30 degree fronto-occipital axial tilt.
It helps in visualization of the temporal bones of, arcuate eminence, mastoid antrum,
superior semicircular canal, internal auditory meatus, cochlea and external auditory
meatus. It is also valuable in the diagnosis of apical petrositis and acoustic neuroma.

10. Axial anatomy from inferior to superior
At the most inferior level we see the facial nerve passing inferiorly to
finally reach the stylomastoid foramen (not shown in this image).
The carotid artery is shown within the carotid canal.
Also at this level is the top of the jugular bulb.
Coronal anatomy
The petrous bone is positioned in an oblique orientation from
posterolateral to anteromedial.
As a result most structures will be sectioned obliquely on coronal
images.
The following coronal images go from anterior to posterior.
First we will see the tympanic membrane with the ossicles, followed
by the cochlea, antrum and semicircular canals.
Finally the most posterior image will show the point where the facial
nerve exits the temporal bone at the stylomastoid foramen.

11. Glenoid fossa
Scissura eardrum
Fascial canal
Mastoid air cells.
Occipital condyle
Jugular foramen.
Foramen magnum
Carotid foramen.
Tensor tympani

12. Fascial canal Jugular foramen.
Tensor tympani
Eustachian tube
Corda tympani canal

13. Fascial canal
Jugular foramen.
Tensor tympani

14. Tensor tympani
Jugular foramen.
Fascial canal
Tympanic membrane
Corda tympani canal

15. Tendon for Tensor tympani
Jugular foramen.Osseous fascial canal
External auditory canal

16. Petrous Apex.
Osseous fascial canal
Inferior handle of malleus
Jugular
foramina.
Jugular Bulb.
Tendon for Tensor tympani

17. Tendon for Tensor tympani
Apical turn of the cochlea
Basal turn of the cochlea
Handle of malleus
Osseous fascial canal

18. Handle of malleus
Long process of Incus
Osseous fascial canal
3rd portion
Tendon for Tensor tympani
Cochlear process
Basal turn of cochlea
Aqueduct of cochlea
Promontory

19. Head of malleus
Wall for middle ear
Body of Incus
Osseous fascial
canal (3rd portion)
Tendon for Tensor tympani
Cochlear process
Round window
Pyramidal eminence

20. Pyramidal eminence
VestibuleOsseous fascial
canal (3rd portion)

21. Ovale Window
Osseous fascial
canal (2nd portion)

22. Osseous fascial
canal (1st portion)
Mastoid antrum
Extreme upper
jugular foramen.

23. Internal acoustic meatus
Mastoid antrum
Aditus ad antrum

24. Aditus ad antrum
Lateral semicircular
canal

25. Mastoid antrum

26. Mastoid antrum
Mastoid foramen
Upper jugular
foramen.
Vestibular aqueduct

27. Mastoid foramens

28. Mastoid
canal
Superior semicircular canal.
Posterior semicircular canal.
jugular foramen.

29. Mastoid antrum
Ear pinna
Foramina for
internal jugular vein

30. internal jugular
vein foramen
Mastoid antrum

31. Mastoid antrum
Ear pinna
internal jugular
vein foramen

32. internal jugular
vein foramen
Posterior
semicircular canal.

33. Aditus ad antrum
Bony canal for
Corda tympanum
3rd portion of osseous fascial canal.
internal jugular
vein foramen
Pyramidal eminence

34. Lateral semicircular canal.
3rd portion of osseous fascial canal.
Ear pinna
internal jugular
vein foramen
Pyramidal eminence
Jugular -facial
foramen

35. Lateral semicircular
canal.
Superior semicircular
canal.
internal jugular
vein foramen
Pyramidal eminence
3rd portion of osseous fascial canal.

36. Lateral semicircular
canal.
Superior semicircular
canal.
internal jugular
vein foramen

37. Superior semicircular
canal.
internal jugular
vein foramen
Cochlear aqueduct
Round window.
Septum
epitympanum
jugulare

38. epitympanum
Round window.
Lateral semicircular
canal.
Tegmen tympani.

39. Lateral semicircular
canal.
2nd portion of
osseous fascial canal.
Ovale window.
Ear drum
Vestibule
Malleous
Epitympanum

40. Epitympanum
Tegmen tympani
Incus
Drum spur
External auditory
meatus
Tympanic membrane
Superior semicircular
canal.
Internal acoustic meatus
Promontory

41. Epitympanum
Tegmen tympani
Drum spur
Tympanic membrane
Handle of malleous
Petrous apex.
1st portion of
osseous fascial canal
Basal turn of cochlea

42. Tympanic
membrane
Drum spur
Tegmen tympani
malleous
1st portion of
osseous fascial canal
Internal acoustic meatus

43. 1st portion of
osseous fascial canal
Cochlea
2nd portion of
osseous fascial canal
Malleous
Head
Neck
Handle
Tendon for Tensor tympani Septum epitympanum jugulare

44. Cochlea
Carotid
canal
Cochlear
process

45. Geniculate
ganglia.
Myotendinous junction
of tensor tympani
Carotid
canal
Apex of
Cochlea
Petrous apex

46. Geniculate
ganglia.
Muscle belly of
tensor tympani
Aditus antrum
Petrous
apex
Carotid
canal

47. Muscle belly of
tensor tympani
Petrous
apex
Carotid
canal
Aditus antrum

48. Head of malleous
Body of incus

49. Spiral laminar bone
with cochlear apex
Cochlea
(basal turn)

50. Pyramidal eminence
Promontory
Sinus tympani.
3rd portion of osseous
fascial canal
Cavernous
Tympanicum

51. The internal auditory canal:
- Has three parts: the internal acoustic meatus (medial opening), the
canal (an average of 8 mm) and the fundus, of irregular shape
(modulates the passage of the VII and VIII cranial nerves).
- Nervous contents: the facial nerve (the largest in size) and the
cochleo-vestibular nerve that divides into the cochlear nerve and the
vestibular nerve which further divides itself into the superior
(innervates the utricle and the ampulla of the superior and lateral
SCC), and the inferior branches (innervates the saccule and the
ampulla of the posterior SCC).
The singular nerve (or the posterior ampullary nerve) has its proper
canal, the singular canal, in the postero-inferior quadrant of the
fundus that can be often be observed with 3T imaging.
- Vascular content: arterial by the labyrinthine artery and venous
with three drainage pathways (internal auditory vein, vein of
cochlear aqueduct and vein of vestibular aqueduct).
The inner ear MR anatomy.

55. Axial section through the inner auditory canal (IAC) and the
labyrinthe with visualization of the cochlear and inferior vestibular
nerves. The utricular macula is also well depicted.

56. Anterior coronal section through the IAC. Outline of the facial nerve in
its complete cisternal course, the cochlear nerve is only partially viewed.

57. Posterior coronal section through the IAC. Vestibular nerve
division and vestibular ganglion (of Scarpa) are visualized.

58. Appearance variant of the vestibular nerve with inferior vestibular division into
the saccular nerve (that innerves the saccule) and the posterior ampullary nerve (for
the ampulla of the posterior semicircular canal). The singular canal is also frequently
observed, not shown in this figure. Coronal and sagittal sections through the IAC.

59. Sagittal seriate sections of the IAC from medial (left), showing the
pontocerebellar cistern, to lateral (right), showing the fundus and inner ear structures.

60. Cochlear nerve at the fundus of the IAC and its passage via the modiolus
to the cochlea in an oblique sagittal section. This finding is of clinical
importance when studying the inner ear malformations.

61. Heavily T2 coronal section respective to the IAC. Vestibular and cochlear
structures are seen, note the utricular macula and spiral lamina.

62. Sagittal section respective to the IAC through the inner ear in a 3D
Heavily T2 sequence. This section is also orthogonal to the macula of
the utricle and unfolds partially the cochlea.

63. Oblique coronal section through the anterior labyrinth
and fundus of the IAC, 3D Heavily T2 sequence.

64. FLAIR sequence in the axial plane four hours after Gd intravenous
injection, the saccule and part of the utricle are visualized.

65. Axial FLAIR Gd sequence through the utricle, the saccule is partially visualized.

66. Heavily T2 in the plane of the lateral semicircular canal (oblique
axial). The ampulla and its ampullary crest (low signal) are seen.

67. FLAIR Gd sequence section in the lateral SCC plane, passing through the utricle.

68. Section in the plane of the superior semicircular canal (plane of
Pöschl, sagittal to the petrous bone), with heavily T2 sequence.

69. Section in the same plane of the superior semicircular canal with FLAIR Gd sequence.

70. T2 sequence in the plane of the posterior SCC (plane of Stenver,
coronal to the petrous bone). Notice the common part of the
superior and posterior semicircular canals, i.e. the common crus.

71. FLAIR and Heavily T2 sequences, sections in the coronal plane. Notice the
position of the utricular macula (T2 sequence) relative to the utricle (FLAIR).

72. Thank You.