Temporal bone radiology

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 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

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

5. 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

6. 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

7. 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:

8. 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.

9. 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.

10. 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

11. 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.

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

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

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

15. 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.

16. 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

17. 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.

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

19. INCUS ž Mesotympanum : Longprocess (LPI) articulates with head of Stapes.   ž Epitympanum : Short process is the most posterior part and points towards aditus . INCUS Body and  Shortprocess ofIncus

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

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

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

23. 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

24. 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

25. 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 .   Semi canal for tensortympani (Stt)

26. 30 Inner ear- Osseous & Membranous Osseous - vestibule Semicircular canals Cochlea

27. 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 Cochlea ž The perilymphaticspace of vestibule iscontinuous with thecochlea anteriorly. ž The cochlea is aconical structure,extends for 2.5-2.75turns ž Promontory  (P) is the projectionraised by the basalturn of cochlea.   Coronal Middle turn Axial

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

29. Axial coronal SSC Axial section: LSC and PSC PS PSC SSC

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

31. 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,

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

33. 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.

34. 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

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

36. 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

37. 47 Carotid canal Jugular fossa Auditory tube Temporo mandibular jt Petro occipital fissure

38. 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.

39. 49 Descending facial nerve Cochlear aqueduct EAC Promontory canal For tensor tympani

40. 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

41. 51 malleus incus stapes Round window

42. 52 Oval window IAC Scala tympani Facial recess

43. 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

44. 54 Ice cream cone appearance Facial nerve canal Internal auditory canal

45. 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

46. 56 LATERAL SC CANAL VESTIBULE IAC PROXIMAL LIMB OF 7 TH N ADITUS TO MASTOID ANTRM VESTIBULAR AQUEDUCT

47. 57 CORONAL SECTIONS 1. Coronal anterior tympanic level -Head of malleus -Tegmen tympani -Basal & 2 nd turn of Cochlea -Geniculate ganglion - scutum

48. 58 COCHLEA IAC HEAD OF MALLEUS SCUTUM GENICULATE GANGLIA SQ TEMP ORAL BONE

49. 59 2.Coronal mid-tympanic level - L shaped incudo-stapedial articulation -Stapes -Oval window - Tegmen tympani

50. 60 IAC Oval Window Incus in aditus Stapes Tegmen tympani

51. 61 3.CORONAL OVAL WINDOW LEVEL IAC Oval window Stapes Lateral SCC

52. 62 Vestibule IAC Sup SCC Antrum Lateral SCC Oval window Middle ear EAC

53. 63 5.Coronal jugular foramen level Jugular foramen Descending facial Nerve Mastoid antrum Occipital bone and atlas

54. 64 Jugular fossa Descending facial nerve Mastoid Air Cells

55. 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

56. 66 7 & 8 th nerve complex Cochlea