cochlear implant imaging

BMCH, Chitradurga

Imaging Requirements for Cochlear Implantation

Dr. Prahlada N.BMBBS, MS, MBA, MHA

ENT, HEAD – NECK & SKULL BASE SURGERYBasaveshwara Medical College & Hospital

Chitradurga

4/16/2013 24/16/2013 2 BMCH, Chitradurga

• Determine patients with Contraindications for CI

• Determine the approach• As a guide during surgery

Why Imaging?Ob

ject

ives


• HRCT temporal bone.• MRI

What type of ImagingPr

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• Evaluates the status of –Mastoid pneumatisation – Thickness of the cortical bone–Middle ear aeration– The round window niche

Role of HRCTPr

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• It may display anatomic middle ear variations of surgical importance such as: – Dehiscent facial nerve – Low lying dura – High jugular bulb and – Aberrant carotid artery

Role of HRCTPr

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• CT demonstrates anomalies of the bony labyrinth such as – Paget’s disease – Otosclerosis – Postmeningitis stenosis of the round

window niche.

Role of HRCTPr

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• HRCT scans are performed on a 64-slice volume scanner in a straight axial plane: kV: 140, mA: 350, matrix: 512 × 512

• Slice thickness: 0.625 mm/10.63, 0.531:1

• Scan field of view (FOV): 32 cm, display FOV: 9.6 cm

HRCTPr

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• The original isometric volume data is used to obtain Coronal reformatted images.

• The images are reviewed with a high-resolution bone algorithm, using a small FOV for separate right and left ear documentation.

HRCTPr

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• Coronal reformations along with 3D maximum intensity projection (MIP) reconstructions.

HRCTPr

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• To identify active fibrosis• Identify cochlear fluid fibrosis• To depict cochlear nerve agenesis

and cochlear anomalies• To detect an occult acoustic nerve

tumour• To detect brainstem anomalies– Trauma, Congenital.

Role of preoperative MRIPr

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• MRI scans are performed on 1.5-T MR with an 8-channel head coil.

• Sedation is used in most patients. • A 3D-FIESTA (fast imaging enabling

steady-state acquisition) axial sequence (TR: 5.5, TE: 1.7/Fr, FOV: 16 × 16, slice thickness: 1.0/−0.5, matrix: 320 × 320, NEX: 6.0) is performed

MRIPr

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• A 3D-FIESTA sequence is also acquired in a DIRECT OBLIQUE SAGGITTAL PLANE (TR: 6.7, TE: 2.1/Fr, FOV: 12 × 12, slice thickness: 1.0/−0.5, matrix: 384 × 320, NEX: 6.0) perpendicular to the VII–VIII nerve complexes.

MRIPr

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ol

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MRI Direct Oblique Saggittal ViewCadaver Dissection showing Direct Oblique Sagittal View.

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MRI Direct Oblique Saggittal View

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MRI - Constructive Interference Steady State (CISS)

Science Photo library

Advantage : Combination of high signal levels andextremely high spatial resolution.


• Provides better resolution than with reformations from an axial sequence; Provides better delineation of the nerves .

• A routine T2W axial sequence through the brain is obtained in all patients.

MRIPr

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• Advantages of MRI over CT:– Distinguish between cochlear fibrosis

and ossification– Diagnose cochlear nerve agenesis. –MRI may depict unsuspected acoustic

nerve or central acoustic pathway anomalies including acoustic nerve tumours.

HRCT Vs MRIPr

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• Disadvantages of MRI– Additive cost as MRI does not replace

CT. – Good quality MR images in deaf

patients are more difficult to obtain, as difficulties of communication may lead to movement artefacts.

– Sedation is needed in children.

HRCT Vs MRIPr

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ol

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NORMAL ANATOMY - HRCTImaging requirements for Cochlear Implantation

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Frontal

Medial

Occipital

Lateral

1. Temporomandibular joint (glenoid roof and articular disc) 2. Pharyngotympanic tube (auditory tube) 3. Internal carotid artery 4. External acoustic meatus 5. Facial canal 6. Internal jugular vein 7. Mastoid process 8. Sigmoid sinus 9 Carotid canal 10. Malleus (handle) 11. Tensor tympani muscle (canal) 12. Middle ear 13. Incus (long limb) 14. Cochlea (basal turn) 15 Sinus tympani 16 Vestibular aqueduct 17 Round window

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2 Malleus (handle) 3 Incus (long limb) 4 Cochlea 5 Stapes 6 Oval window 7 Sinus tympani 8 Facial canal 9 Internal jugular vein (bulb) 10 Mastoid 11 Epitympanic recess 12 Malleus (head) 13 Incus (short limb) 14 Internal acoustic meatus15 Aditus to mastoid antrum 16 Vestibule 17 Posterior semicircular canal 18 Mastoid antrum 19 Lateral semicircular canal

Frontal

Medial

Occipital

Lateral

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1 Geniculate ganglion 2 Facial nerve (first part) 3 Facial nerve (second part) 4 Internal acoustic meatus 5 Tympanic cavity6 Vestibule 7 Posterior semicircular canal 8 Mastoid antrum 9 Lateral semicircular canal 10Sigmoid sinus 11 Anterior (superior) semicircular canal 12 Mastoid cells

Frontal

Medial

Occipital

Lateral

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Frontal

Medial

Occipital

Lateral

1 Geniculate ganglion 2 Facial nerve (first part) 3 Facial nerve (second part) 4 Internal acoustic meatus 5 Tympanic cavity6 Vestibule 7 Posterior semicircular canal 8 Mastoid antrum 9 Lateral semicircular canal 10 Sigmoid sinus 11 Anterior (superior) semicircular canal 12 Mastoid cells

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NORMAL ANATOMY - MRIImaging requirements for Cochlear Implantation.

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Inferior view of 3D maximum intensityprojection (MIP) reconstructed from 3T MR.

Note the cochlear nerve anteriorly and both saccular and posterior branches of the inferior vestibular nerves posteriorly.

John I. Lane Robert J. Witte: The Temporal Bone, An Imaging Atlas

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Superior view of 3D MIP reconstructed from 3T MR.

Note the facial nerve anteriorly and the superior vestibular nerve posteriorly

John I. Lane Robert J. Witte: The Temporal Bone, An Imaging Atlas

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PRE-SURGICAL EVALUATIONImaging requirements for Cochlear Implantation


• An IAM less than 2 mm in diameter increases the risk of a congenital absence or of severe hypoplasia of the acoustic nerve.

• An absent or narrow modiolus (diameter less than 3 mm in CT, or a modiolar surface less than 4 mm2 in MR) are at risk of absence of cochlear nerve.

• The modiolus is a bone area of low signal intensity in T2WI, located at the base of the cochlea. It represents the exit of the cochlear nerve.

1. Size of the IAMKe

y Po

ints


• Exploration of the IAM by MR with CISS sequence and sagittal reconstructions allows the measurement of the diameter of the cochlear nerve.

• Cochlear nerve diameter is measured in relation to the facial nerve taken as reference.

• Normally, the cochlear nerve lays on the inferior part of the IAM and

• Cochlear nerve is larger than the facial nerve.• Its diameter is approximately of 0.4 mm.

3. Cochlear nerve statusKe

y Po

ints

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ModiolusThe modiolus is a conical shaped central axis in the cochlea. It consists of spongy bone and the cochlea turns approximately 2.5 times around it. The spiral ganglion is situated inside it.

Basic human anatomy - O'rahilly, Müller, Carpenter & Swenson

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Cochlear nerve deficiencyC. Isolated Cochlea. D. Absent Cochlear Nerve.

Christine M. Imaging Findings of Cochlear Nerve Deficiency. AJNR 2002 23: 635-643

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Absent ModiolusAxial section of the cochlea of a 4-year-old boy with Cornelia de Lange syndrome. Note the diminished width and height of cochlear upper turns with an absent modiolus in the section from the patient with Cornelia de Lange syndrome (A) as compared with a 2-year-old control with normal hearing (B).

J. Kima: Temporal Bone CT Findings in Cornelia de Lange Syndrome. AJNR March 2008 29: 569-573

http://www.ajnr.org/content/29/3/569.abstract


• Anomaly of the course of the:• Facial nerve • The carotid artery • The sigmoid sinus • Venous variants such mastoid

emissary veins

2. Neurovascular AnomalyKe

y Po

ints


• Facial nerve with an abnormal course through the mastoid cells is at significant risk during implantation.

• Facial nerve injury can occur during

– Facial recess approach. – Insertion of electrodes.

• Facial nerve monitoring is an option.

2. Neurovascular AnomalyKe

y Po

ints


• Study:– The number of cochlear turns – Symmetry of scala chambers– Status of the modiolus – Status of the posterior membranous

labyrinth.

4. Membranous labyrinth anomaly

Key

Poin

ts


• Congenital anomalies discovered during preoperative imaging studies can be the cause of the sensorineural hearing loss.

• Can increase the surgical risk to have a `Gusher-ear' during the electrode insertion within the round window

4. Membranous labyrinth anomaly

Key

Poin

ts


• Cochlear ossification or fibrosis may:– Limit the full insertion of the electrode

array or –Modify the choice of the cochlear

implant–Modify the way of Electrode insertion.

5. Endo- and perilymphatic fluid StatusKe

y Po

ints


• Stenosis of the round window niche may occur in bone remodelling lesions such as:– Paget’s disease– Otosclerosis– Lobstein disease – Post-meningitis labyrinthitis.

6. Status of Bony Labyrinth & Round Window Niche

Key

Poin

ts

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Paget’s DiseaseAxial CT scan demonstrates diffuse expansion and sclerosis of the bones of the skull base, characteristic of Paget disease.

S. Vattotha, et al. A Compartment-Based Approach for the Imaging Evaluation of Tinnitus. AJNR 2010 31: 211-218

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OtosclerosisFenestral otosclerosis showing a fissula ad fenestram.

Medical Observer. Australia

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Osteogenesis ImperfectaThe labyrinthine segment, the geniculate ganglion (arrowheads), and the proximal tympanic segment of the facial nerve canal are severely involved and have indistinct, irregular margins. Progression of demineralization is also demonstrated in pericochlear areas

Osteogenesis Imperfecta of the Temporal Bone: CT and MR Imaging in Van der Hoeve-de Kleyn SyndromeHatem Alkadhi . AJNR 2004 25: 1106-1109

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Post-meningitis labyrinthitis. Axial CT scan showing advanced labyrinthitis ossificans in both ears.

Vanessa Y.J. Tan et al: Acoustic brainstem implant in a post-meningitis deafened child—Lessons learned. International Journal of Pediatric Otorhinolaryngology Volume 76, Issue 2, February 2012, Pages 300–302

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CONGENITAL ANOMALIESImaging requirements for Cochlear Implantation


• Cochlear• Vestibular• Semicircular canal, • Internal auditory canal (IAC)• Vestibular and • Cochlear aqueduct malformations.

Types of anomaliesCl

assifi

catio

n

Sennaroglu L, Saatci I. Laryngoscope. 2002;112:2230–41.


• Michel deformity• Common cavity deformity• Cochlear aplasia• Hypoplastic cochlea• Incomplete partition types– I (IP-I) and – II (IP-II) (Mondini deformity).

Cochlear anomaliesCl

assifi

catio

n



• Incomplete partition type I or Cystic cochleovestibular malformation:– Cochlea lacks the entire modiolus and

cribriform area, resulting in a cystic appearance, and there is an accompanying large cystic vestibule.

Incomplete partition of Cochlea

Clas

sifica

tion


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Incomplete partition type I or Cystic cochleovestibular malformation

Axial Section showing Cystic appearing Cochlear and Large cystic Vestibule.

University of Washington Department of Radiology.

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Common cystic cavity


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Incomplete partition - II Classic Mondini malformation


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Incomplete partition variant Normal basal turn of the Cochlear and Round Window


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Incomplete partition variant 1.5 Turns of Cochlear with Confluence of the middle and apex resulting in Cystic apex. Enlarged vestibule with nomral Vestibular aqueduct are seen.



• Incompelete Partition Type II or the Mondini deformity:– A cochlea consisting of 1.5 turns (in

which the middle and apical turns coalesce to form a cystic apex accompanied by a dilated vestibule and enlarged vestibular aqueduct.

Incomplete partition of Cochlea

Clas

sifica

tion


• Michel deformity• Cochlear aplasia• Common cavity • Cochlear hypoplasia• IP-I (Cystic cochleovestibular

malformation), • IP-II (Mondini deformity)

Clinical ClassificationCl

assifi

catio

n



• Absent Cochlear nerve– Diameter of IAM (mid-part) <3 mm

• Absent Cochlear• Absent Modiulus

Contraindications for CINo

to C

I


• Cochlear ossification (partial or total; length in basal turn)

• Hyperostosis of the round window niche

• Persistent membranous labyrinth inflammation

• Inner ear at risk of `Gusher': endolymphatic sac dilatation.

Alternate Surgical Technique/Implant Device

No to

CI


• Abnormal cochlear segmentation.• Deficient modiolus.• Semicircular canal or vestibular

dilatation.• Stenosis of the basal turn.• Otosclerosis foci.• Paget’s disease.

Alternate Surgical Technique/Implant Device

No to

CI

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Deficient ModiolusAxial T2-weighted FSE MR image of the right inner ear : The cochlear outline is distorted, and the normal notch between the middle and apical turns laterally (white arrow) is blunted. Note that the modiolus is deficient (black arrow).

H. Christian Davidson: MR Evaluation of Vestibulocochlear Anomalies Associated with Large Endolymphatic Duct and Sac. AJNR 1999 20: 1435-1441

,

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Deficient ModiolusAxial T2-weighted FSE MR image in another patient shows severe dysplasia. The cochlea (C) appears as a common cavity, the internal architecture is lost, and the modiolus is absent. The vestibule also shows severe dysplastic changes, including gross vestibular enlargement (V) and hypoplasia of the lateral semicircular canal (arrowhead). A portion of the enlarged endolymphatic duct is also apparent (asterisk).

H. Christian Davidson: MR Evaluation of Vestibulocochlear Anomalies Associated with Large Endolymphatic Duct and Sac. AJNR 1999 20: 1435-1441

,

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Otosclerosis of the CochleaDuring surgery it was noted that otosclerosis had filled the basal turn of the cochlea and obliterated the round window.

Eric W. Sargent M.D., OTOSCLEROSIS: A Review for Audiologists

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Stenosis of the Basal Turn of the Cochlear

Small calcification in basal turn of cochlea as a result of labyrinthitis ossificans.

Eric Beek and Frank Pameijer: Temporal Bone Pathology.

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Semicircular Canal dilatationThere is a widening and shortening of the lateral semicircular canal.


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Vestibular dilatationThe vestibule is relatively large (arrow).



• Hypoplastic mastoid process• Inflammed middle ear• Dehiscent or aberrant facial nerve• Mastoid emissary vein• Deep sigmoid sinus• Exposed jugular bulb• Aberrant carotid artery• Persistent stapedial artery

Increased Surgical Risk No

to C

I

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Hypoplastic Mastoid ProcessRight side, the mastoid air cells are under pneumatized. There is no identifiable external auditory canal.

American College of Radiology

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Normal Vs Sclerosed MastoidFirst: Normal pneumatized mastoid with aerated cells. The mastoid is completely sclerotic - no air cells are present.

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Chronic Otitis MediaThe eardrum is thickened. A small amount of soft tissue (arrow) is visible between the scutum and the ossicular chain but no erosion is present. This favors the diagnosis of chronic otitis media.

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Dehiscent Facial Nerve

Robert J. Witte, MD: Pediatric and Adult Cochlear Implantation: RadioGraphics 2003; 23:1185–1200

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Dehiscent Facial NervePatient also has signs of Chronic Otitis Media

NIRA A. GOLDSTEIN, MD et al., Intratemporal complications of acute otitis media in infants and children. Otolaryngology - Head and Neck Surgery Volume 119, Issue 5, November 1998, Pages 444–454.

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Mastoid Emissary Vein

H Alsherhri1, B Alqahtani2, M Alqahtani3: Year : 2011 | Volume : 17 | Issue : 3 | Page : 123-126

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Anterior Bulging Sigmoid SinusThe sigmoid sinus can protrude into the posterior mastoid.It can be accidentally lacerated during a mastoidectomy .

Temporal bone – Pathology: Eric Beek and Frank PameijerRadiology department of the University Medical Centre of Utrecht, the Netherlands

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High Jugular BulbThe jugular bulb is often asymmetric, with the right jugular bulb usually being larger than the left. If it reaches above the posterior semicircular canal it is called a high jugular bulb.


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Jugular Bulb DiverticulumRarely an out-pouching is seen – this is known as a jugular bulb diverticulum.


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Dehiscent jugular bulbOn the left a dehiscent jugular bulb (blue arrow). This can be dangerous during myringotomy. Note also the bulging sigmoid sinus (yellow arrow).


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Persistent Stapedial Artery

www.neuroangio.org

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Aberrant internal carotid arteryIn patients with an aberrant internal carotid artery the cervical part of the internal carotid artery is absent. It is replaced by the ascending pharyngeal artery which connects with the horizontal part of the internal carotid artery. It courses through the middle ear.


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Aberrant internal carotid arteryOn the left coronal images of the same patient. On the right side the internal carotid artery is separated from the middle ear (blue arrow). On the left side the internal carotid artery courses through the middle ear (red arrow)


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