How to read ct scan temporal bone - A dhulikhel hospital, kathmandu university hospital protocol

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 1

2. Why it is necessary?? To identify the anatomy. For the surgical planning. To assess the risk. Informed consent. 7/21/2020 Prof Dr. Bikash Lal Shrestha 2

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 3

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 4

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 5

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. 7/21/2020 Prof Dr. Bikash Lal Shrestha 6

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 . 7/21/2020 Prof Dr. Bikash Lal Shrestha 7

8. PNEUMATISATION AND VENTILATION OF MASTOID AIR CELLS 7/21/2020 Prof Dr. Bikash Lal Shrestha 8

9. Well pneumatized and ventilated mastoid on right side Poorly pneumatized mastoid air cells on right side 7/21/2020 Prof Dr. Bikash Lal Shrestha 9

10. Well pneumatized and poorly ventilated mastoid air cells on right side Well pneumatized and well ventilated mastoid air cells on left side 7/21/2020 Prof Dr. Bikash Lal Shrestha 10

11. EXTERNAL AUDITORY CANAL AND TYMPANIC MEMBRANE 7/21/2020 Prof Dr. Bikash Lal Shrestha 11

12. External auditory canal anterior wall External auditory canal posterior wall Tympanic membrane 7/21/2020 Prof Dr. Bikash Lal Shrestha 12

13. OSSICULAR CHAIN 7/21/2020 Prof Dr. Bikash Lal Shrestha 13

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 14

15. Stapes crura : Looks like arc shaped . Stapes anterior crura Stapes posterior crura Lenticular process of incus 7/21/2020 Prof Dr. Bikash Lal Shrestha 15

16. Oval window and Round window 7/21/2020 Prof Dr. Bikash Lal Shrestha 16

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 17

18. Round window: Lies inferior to promontory. Covered by round window niche. Promontory Round window niche Round window membrane 7/21/2020 Prof Dr. Bikash Lal Shrestha 18

19. INNER EAR 7/21/2020 Prof Dr. Bikash Lal Shrestha 19

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. 7/21/2020 Prof Dr. Bikash Lal Shrestha 20

21. Long axis of temporal bone Superior semicircular canal – perpendicular to long axis 2 limbs of superior semicircular canal Cobra eye appearance 7/21/2020 Prof Dr. Bikash Lal Shrestha 21

22. POSTERIOR SEMICIRCULAR CANAL It lies parallel to the long axis of temporal bone . On scrolling, it is seen below Superior semicircular canal. 7/21/2020 Prof Dr. Bikash Lal Shrestha 22

23. Posterior semicircular canal lies parallel to long axis of temporal bone Long axis of temporal bone Crus commune 7/21/2020 Prof Dr. Bikash Lal Shrestha 23

24. LATERAL SEMICIRCULAR CANAL AND VESTIBULE It looks signet ring appearance. 7/21/2020 Prof Dr. Bikash Lal Shrestha 24

25. Lateral s emicircular canal Vestibule Signet ring appearance Lateral semicircular canal Vestibule Posterior semicircular canal 7/21/2020 Prof Dr. Bikash Lal Shrestha 25

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 26

27. COCHLEA Stack of coins appearance Basal turn Mid turn Apical turn 7/21/2020 Prof Dr. Bikash Lal Shrestha 27

28. Carotid artery lie just anteroinfero and medial to the basal turn of cochlea 7/21/2020 Prof Dr. Bikash Lal Shrestha 28

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. 7/21/2020 Prof Dr. Bikash Lal Shrestha 29

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 30

31. FACIAL NERVE In axial cut from superior to inferior, the different segments of facial nerve can be identified. 7/21/2020 Prof Dr. Bikash Lal Shrestha 31

32. Meatal segment of facial nerve within internal auditory meatus Meatal foramen 7/21/2020 Prof Dr. Bikash Lal Shrestha 32

33. Labyrinthine segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 33

34. First genu Tympanic segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 34

35. Tympanic segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 35

36. Vertical/mastoid segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 36

37. Vertical/mastoid segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 37

38. CORONAL IMAGE Check for the scutum/ tegmen tympani (dural plate), and the bone covering the lateral semicircular canal. 7/21/2020 Prof Dr. Bikash Lal Shrestha 38

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 Mesotympanum 7/21/2020 Prof Dr. Bikash Lal Shrestha 39

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 40

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 7/21/2020 Prof Dr. Bikash Lal Shrestha 41

42. Fallopian canal lying just inferior to lateral canal Lateral semicircular canal Round window Oval window Superior semicircular canal 7/21/2020 Prof Dr. Bikash Lal Shrestha 42

43. Mastoid segment of facial nerve in coronal cut 7/21/2020 Prof Dr. Bikash Lal Shrestha 43

44. Surgically Important Spaces within the temporal bone 7/21/2020 Prof Dr. Bikash Lal Shrestha 44

45. Cog Prussak’s space Fossa incudis 7/21/2020 Prof Dr. Bikash Lal Shrestha 45

46. 7/21/2020 Prof Dr. Bikash Lal Shrestha 46 Prussak's space

47. Sinus tympani Facial recess Pyramid Vertical segment of facial nerve 7/21/2020 Prof Dr. Bikash Lal Shrestha 47

48. EUSTACHIAN TUBE Opening of the Eustachian tube – completely aerated and patent 7/21/2020 Prof Dr. Bikash Lal Shrestha 48

49. THANK YOU FOR WATCHING. 7/21/2020 Prof Dr. Bikash Lal Shrestha 49