Imaging requirements for cochlear implantation

Imaging Requirements for Cochlear Implantation

Imaging Requirements for Cochlear ImplantationDr. Prahlada N.BMBBS, MS, MBA, MHAENT, HEAD NECK & SKULL BASE SURGERYBasaveshwara Medical College & Hospital Chitradurga

BMCH, Chitradurga

Imaging Requirements for Cochlear Implantation. Dr. Prahlada N.BMBBS, MS, MBA, MHAENT, HEAD - NECK SURGERY & SKULL BASE SURGERYBasaveshwara Medical College & Hospital Chitradurga

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Determine patients with Contraindications for CIDetermine the approachAs a guide during surgeryWhy Imaging?Objectives

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HRCT temporal bone.MRIWhat type of ImagingProtocol


Evaluates the status of Mastoid pneumatisation Thickness of the cortical boneMiddle ear aerationThe round window niche Role of HRCTProtocol


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 HRCTProtocol


CT demonstrates anomalies of the bony labyrinth such as Pagets disease Otosclerosis Postmeningitis stenosis of the round window niche.

Role of HRCTProtocol


HRCT scans are performed on a 64-slice volume scanner in a straight axial plane: kV: 140, mA: 350, matrix: 512 512Slice thickness: 0.625 mm/10.63, 0.531:1Scan field of view (FOV): 32 cm, display FOV: 9.6 cm

HRCTProtocol


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.

HRCTProtocol


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

HRCTProtocol


To identify active fibrosisIdentify cochlear fluid fibrosisTo depict cochlear nerve agenesis and cochlear anomaliesTo detect an occult acoustic nerve tumourTo detect brainstem anomaliesTrauma, Congenital.Role of preoperative MRIProtocol


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 MRIProtocol


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 VIIVIII nerve complexes.

MRIProtocol


MRI Direct Oblique Saggittal View

Cadaver 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 libraryAdvantage : Combination of high signal levels andextremely high spatial resolution.

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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.MRIProtocol


Advantages of MRI over CT:Distinguish between cochlear fibrosis and ossificationDiagnose cochlear nerve agenesis. MRI may depict unsuspected acoustic nerve or central acoustic pathway anomalies including acoustic nerve tumours.HRCT Vs MRIProtocol


Disadvantages of MRIAdditive 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 MRIProtocol


Normal anatomy - hrctImaging requirements for Cochlear Implantation

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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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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

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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

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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

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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 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

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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 IAMKey Points


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

3. Cochlear nerve statusKey Points


Modiolus

Themodiolusis a conical shaped central axis in thecochlea. It consists of spongy bone and the cochlea turns approximately 2.5 times around it.Thespiral ganglionis situated inside it.Basic human anatomy - O'rahilly, Mller, Carpenter & Swenson

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

Christine M. Imaging Findings of Cochlear Nerve Deficiency. AJNR200223:635-643

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Congenital absence of the cochlear nerve with an isolated cochlea. Axial and oblique sagittal T2-weighted fast spin-echo MR images of a 5-year-old girl with profound unilateral hearing loss (patient C8).A, Image of the normal left side shows the normal contours of the cochlea and other labyrinthine structures.B, IAC is of normal size and contains four nerves of comparative size. Cochlear nerve lies anteroinferiorly (arrow).C, Right side shows a deformed contour of the IAC (black arrow). Low-signal-intensity bar separates the fundus of the IAC from the modiolus (white arrow), which was confirmed to be bony at CT. We describe this as an isolated cochlea. Thearrowheadindicates a singular canal containing the nerve of the posterior semicircular canal.D, Oblique sagittal image of the distal IAC shows a solitary nerve within the superior aspect of the small, deformed canal (arrow). The cochlear nerve is absent in this patient with normal facial nerve function.

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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. AJNRMarch 200829:569-573

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

2. Neurovascular AnomalyKey Points


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 AnomalyKey Points


Study:The number of cochlear turns Symmetry of scala chambersStatus of the modiolus Status of the posterior membranous labyrinth. 4. Membranous labyrinth anomalyKey Points


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 anomalyKey Points


Cochlear ossification or fibrosis may:Limit the full insertion of the electrode array or Modify the choice of the cochlear implantModify the way of Electrode insertion.

5. Endo- and perilymphatic fluid StatusKey Points


Stenosis of the round window niche may occur in bone remodelling lesions such as:Pagets diseaseOtosclerosisLobstein disease Post-meningitis labyrinthitis.

6. Status of Bony Labyrinth & Round Window NicheKey Points


Pagets Disease

Axial 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. AJNR201031:211-218

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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 . AJNR200425:1106-1109

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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 childLessons learned. International Journal of Pediatric Otorhinolaryngology Volume 76, Issue 2, February 2012, Pages 300302

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Congenital anomaliesImaging requirements for Cochlear Implantation

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CochlearVestibularSemicircular canal, Internal auditory canal (IAC)Vestibular and Cochlear aqueduct malformations. Types of anomaliesClassificationSennaroglu L, Saatci I. Laryngoscope. 2002;112:223041.


Michel deformityCommon cavity deformityCochlear aplasiaHypoplastic cochleaIncomplete partition typesI (IP-I) and II (IP-II) (Mondini deformity). Cochlear anomaliesClassificationSennaroglu L, Saatci I. Laryngoscope. 2002;112:223041.


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 CochleaClassificationSennaroglu L, Saatci I. Laryngoscope. 2002;112:223041.


Incomplete partition type I or Cystic cochleovestibular malformationAxial 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 - 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. University of Washington Department of Radiology.

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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 CochleaClassification


Michel deformityCochlear aplasiaCommon cavity Cochlear hypoplasiaIP-I (Cystic cochleovestibular malformation), IP-II (Mondini deformity)Clinical ClassificationClassificationSennaroglu L, Saatci I. Laryngoscope. 2002;112:223041.


Absent Cochlear nerveDiameter of IAM (mid-part)

Imaging requirements for cochlear implantation

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