1. Navigating the Temporal Bone and IAC to Reveal Hearing Loss Pathology: A Diagnostic Algorithm. ASNR Presentation Number:   eEdE-143
Rajesh Gupta MD
Ammar Chaudhry MD
Margaret Whelan MD
Luboslav Woroch DO
Robert Peyster MD

2. No disclosures to report.

3. Outline
Overview Internal Auditory Canal (IAC) MRI anatomy and search pattern with images
Temporal bone CT search pattern with select images
Algorithms based on location and category
Example Cases

4. IAC MRI Anatomy and Search Pattern :
3D CISS sequence (thin axial high T2 sequences)
Review axial images superior to inferior
Look at CN V and Meckel’s cave
Look at Petrous Apex

5. IAC MRI Anatomy and Search Pattern :
3D CISS sequence (thin axial high T2 sequences)
Look at the Cerebellopontine angle
Look at the IAC and evaluate it’s origin

6. IAC MRI Anatomy and Search Pattern :
3D CISS sequence (thin axial high T2 sequences)
Notice CN 7 & 8 in the IAC and their close relationship to AICA
More inferiorly, evaluate the cochlear and vestibular nerves

7. IAC MRI Anatomy and Search Pattern : 3D CISS sequence
Sagittal Multiplanar Reconstruction (MPR) through the IAC
(nerve anatomy within the canal)
Superior
Superior Vestibular n.
Facial n
Falciform crest
Anterior
Cochlear n
Inferior Vestibular n.
The IAC is divided superiorly and inferiorly by a bony lamina (falciform crest):
Smaller superior part: Larger Inferior part:
Superior vestibular n Inferior vestibular n.
Facial n Cochlear n.
Bill’s Bar divides the superior portion of the canal anterior to posterior

8. IAC MRI Anatomy and Search Pattern :
3D CISS sequence (thin axial high T2 sequences)
Finally:
Evaluate the following fluid filled structures that are T2 bright:
Semicircular canals
Vestibule
Ovoid in shape
Cochlea
Modiolus: hypointense area at base
Click to Return to Outline

9. CT Temporal Bone Search Pattern with selected images :
Use both axial and coronal CT images
Start from outside to in:
EAC
Scutum (s)
Tympanic membrane (#)
Epitympanum (e)
Prussak’s space (*)
Mesotympanum (m)
Hypotympanum
Pyramidal eminence (*)
Sinus tympani (st - medially)
Facial n. recess (fnr -laterally)
Ossicles
Malleus
Incus
Stapes
Oval window e s * m
EAC #
Cor
malleous
incus
stapes
fnr st *
Axial

10. CT Temporal Bone Search Pattern with selected images :
Use both axial and coronal CT images
Otic capsule:
Superior semicircular canal (SCC)
Posterior SCC (P)
Lateral SCC (L)
Vestibule (v)
Aditus ad antrum (A)
Cochlea
Modiolus (mo)
Basal turn (b)
Middle turn (m)
Apical turn
IAC
Facial n.
labyrinthine segment (Fnl)
geniculate segment
tympanic segment
Vestibular aqueduct
Fnl A L
IAC v P
Axial
Fnl mo b m
Cor

11. CT Temporal Bone Search Pattern with selected images :
Other structures/landmarks:
Styloid process
Stylomastoid foramen
Petrous apex
Mastoid air cells
Sigmoid sinus
Cochlear promontory
Carotid canal
Tegmen
Jugular bulb
Petrous portion of the temporal bone
Tegmen
Cochelar promontory
Carotid canal
Cor
Click to Return to Outline

12. Sensorineural hearing loss algorithm (click on blue text to go to case)
Location
Cochlea/semicircular canals – likely congenital
Cochlear dysplasia – Incomplete Partition 1 and 2
Enlarged vestibular aqueducts
Enlarged vestibular aqueduct syndrome
Common cavity malformation
Labyrinth – abnormal mineralization
Bony labyrinth with lytic foci – Otospongiosis (mixed hearing loss)
Membranous labyrinth – Labyrinthitis ossificans
Trauma – fracture (acquired)
Cerebellopontine angle and/or Internal auditory canal
Vestibular schwanoma
Meningioma
Epidermoid cyst
Glomus tumor
Lymphoma
Sarcoid
Brainstem
Neoplasms
Multiple sclerosis

13. Conductive hearing loss algorithm (click on blue text to go to case)
Location
External Auditory Canal
Congenital
Atresia/stenosis
Inflammatory
Cholesteatoma
Keratois obturans
Neoplasm
Exostosis, osteoma
Squamous Cell Carcinoma
Infectious
Otitis Externa
Tympanic Membrane
Perforation
Chronic Inflammation
Myringosclerosis
Location
Middle Ear
Congenital
Ossicular anomalies
Cholesteatoma
Aberrant carotid artery
Aberrant facial nerve
Persistant stapedial artery
Inflammatory
Acquired Cholesteatoma
Neoplasm
Glomus tympanicum
Facial neuroma
Meningioma
Infectious
Otitis Media
Trauma
Ossicular disruption
Hemotympanum
Click to Return to Begining

14. Selected Cases

15. Enlarged Vestibular Aqueduct Syndrome (EVAS) :
2 year old F with bilateral sensorineural hearing loss.
6mm
5 mm
A: CT Rt axial
B: CT Lft axial
Bilateral enlarged vestibular aqueducts are shown (yellow arrows). Measurements are shown at the operculum (red lines). At the midpoint , between the crus and aperture, the aqueducts measured 3 mm bilaterally.
Normal < 1.5 midpoint Normal < 1.9 operculum
Click to Return to Algorithm

16. Common Cavity Malformation :
11 month old M with left sensorineural hearing loss.
Confluence of the cochlea, vestibule, and semicirucular canals forming a common cavity
Normal Cochlea
A: CT Rt axial
C: CT Lft axial
Normal:
Superior Semicircular canal,
Vestibule, and
Basal turn of cochlea
Common cavity
Widened IAC
B: CT Rt coronal
D: CT Lft coronal
Click to Return to Algorithm

17. Complex cholesterol granuloma :
Click to Return to Algorithm
Complex cholesterol granuloma :
19 year old M with sudden onset left sensorineural loss, severe vertigo and facial paralysis.
A: MR T1WI Pre-Contrast
B: MR T2WI
Figure A:– Large expansile T1 hyperintense lesion (yellow arrows) at the left petrous apex, jugular foramen and IAC. The lesion involves the 7th and 8th cranial nerve complex leading to sensorineural deafness. B – This lesion exhibits T2 hyperintensity (yellow arrows) and rim of T2 hemosiderin (white arrow). On post contrast imaging, there was no central enhancement but faint peripheral enhancement. The patient required trans-mastoid drainage with resolution of symptoms.

18. Vestibular Schwanoma :
44 year old M with left sensorineural hearing loss.
A: MR axial T2 FLAIR
B: MR axial T1 Post
C: MR cor T1 Post
Figure A: Heterogeneous, FLAIR hyperintense 4.8 cm extra-axial mass in the left cerebellar pontine angle extending into the internal auditory canal with widening and involvement of the vestibular n. (yellow arrow)
Figures B & C: Heterogeneous enhancement with central cavitation representing necrosis (yellow arrows). There is mass effect on the pons and left cerebellum with stenosis of upper 4th ventricle causing mild hydrocephalus.
Click to Return to Algorithm

19. 48 year old F with left sensorineural hearing loss.
Epidermoid :
48 year old F with left sensorineural hearing loss.
A: MR T1 axial
B: MR DWI axial
C: MR DWI axial
Figure A: Lesion at the cerebellopontine angle involving the left internal auditory canal and nerve complex that is isointense to CSF on T1WI (yellow arrow).
Figures B & C: The lesion is hyperintense on DWI and dark on ADC (not shown) due to restricted diffusion, without post contrast enhancement (not shown) suggesting the diagnosis of an Epidermoid tumor over an arachnoid cyst (yellow arrows).
Click to Return to Algorithm

20. Internal Auditory Canal (IAC) Atresia :
5 year old M with left sensorineural hearing loss.
Absent Lft IAC
Absent Lft IAC
Normal Rt IAC
Normal Rt IAC
A: MR axial T2 FLAIR
B: MR axial T2
Absent Lft IAC
C: MR mip axial IAC
Click to Return to Algorithm

21. 59 year old F with right mixed hearing loss.
Otospongiosis :
59 year old F with right mixed hearing loss.
No lucency
A: CT Rt axial
B: CT Lft axial
Figure A: Punctate focus of lucency in the region of the fistula antefenestrum (ie. In front of the oval window) consistent with fenestral (stapedial) otospongiosis.
The retro-fenestral (cochlear) subtype is less common and involves demineralization of the cochlear capsule.
Figure B: Normal left side for comparison.
Click to Return to Algorithm

22. Otitis Externa :
7 year old F with fever, left ear swelling, tenderness, erythema, discharge and intermittent left sided conductive hearing loss.
A: CT Rt axial
B: CT Lft axial
Soft tissue attenuation material within the external auditory canal with abnormal enhancement (Fig C). Canal is obliterated medially with extension into the middle ear cavity.
Normal Rt external ear canal with small focus of cerumen.
C: CT Head post contrast axial
Click to Return to Algorithm

23. Congential Cholesteatoma :
2 year old M with left conductive hearing loss.
A: CT Rt axial
C: CT Lft axial
B: CT Rt cor
D: CT Lft cor
A 3 mm nodular soft tissue density (yellow arrows) is identified along the left tensor tympani tendon and inferomedial to the malleus (manubrium). There is no associated bony erosion differentiating it from acquired cholesteatoma. Normal right side shown for comparison (Figures A &B)
Click to Return to Algorithm

24. Acquired Cholesteatoma :
39 year old F with left conductive hearing loss.
Clear Middle ear cavity
A: CT Rt axial
C: CT Lft axial
Soft tissue density within the middle ear cavity. It obliterates Prussak’s space and erodes the scutum and ossicles.
Normal Scutum
B: CT Rt cor
D: CT Lft cor
Click to Return to Algorithm

25. External Auditory Canal (EAC) Atresia :
14 year old M with right conductive hearing loss.
Absent EAC
Normal EAC
A: CT Rt axial
C: CT Lft axial
Normal size malleus/incus and middle ear cavity
Small malleus and middle ear cavity
Absent EAC
B: CT Rt coronal
D: CT Lft coronal
Click to Return to Algorithm

26. Squamous Cell Carcinoma involving EAC :
77 year old M with right conductive hearing loss.
A: MR T1 post axial
B: MR T1 post cor
A lobulated, heterogeneously enhancing extracranial tumor is shown arising in the right infratemporal region (yellow arrows). It extends from the right pinna to the inferior aspect of the parotid gland and obliterates a portion of the external auditory canal.
Click to Return to Algorithm

27. Click to Return to Algorithm
Trauma :
42 year old M with left conductive hearing loss s/p trauma with blood in left ear. *
A: CT Rt axial
C: CT Lft axial
B: CT Rt cor
D: CT Lft cor
Longitudinal fracture of mastoid and petrous portions of the left temporal bone which also involves the left external auditory canal and middle ear cavity (yellow arrows). Hemorrhage within the left epitympanum , hypotympanum, left EAC, and mastoid air cells (red arrows). The left carotid canal is intact (*). Normal Rt side for comparison.

28. References :
Huang BY, Zdanski C, Castillo M. Pediatric sensorineural hearing loss, part 1: Practical aspects for neuroradiologists. AJNR Feb; 33:
Joshi VM, Navlekar SK, Kishore GR, Reddy KJ, Kumar EC. CT and MR imaging of the inner ear and brain in children with congenital sensorineural hearing loss. Radiographics Jun; 32:
Weissman JL. Hearing Loss. Radiology Jun; 199:
Contact :
Rajesh Gupta MD