I - COCHLEAR IMPLANT :

A- General Information :

A device enabling the transduction of sound energy into a coded electrical signal transmitted to the spiral ganglia, bypassing pathological cochlear cells. 

It consists of two parts (Figure 1): 

   An external part containing: 

     - A microphone placed behind the ear. 

     - A speech processor: encoding electrical impulses.

  An internal part containing (Figure 2):

  The implant itself, or receiver, surgically placed in the mastoid opposite the coil.

  The electrode bundle is inserted into the cochlea and extending the receiver.

B- Functioning of the cochlear implant :

       The steps involved in the functioning of a cochlear implant:

         B-1 - Sound capture by the microphone of the audio processor. 

         B-2 - Analysis and encoding sounds by the audio processor into specific sequences of electrical impulses. 

         B-3 - Sending and transmitting the electrical impulses to the implant itself. 

         B-4 Transmission of the impulses from the implant to the electrodes in the cochlea. 

         B-5 Relaying the electrical signals to the auditory centers of the brain, which interpret them as sounds.

C- Indications: According to HAS 2012 :

              C-1 For Children:

- In cases of pre-lingual deafness: Implantation should be performed as early as possible. Early implantation yields better and faster results in terms of language comprehension and production compared to late implantation. 

- Beyond the age of 5, in cases of profound or total congenital non-progressive deafness, implantation is only indicated (except in special cases) if the child has developed an inclination for oral communication. 

- If the child has already entered into oral communication, they may benefit from implantation at any age. Young adults with congenital deafness can also be implanted.

              C-2 For Adults:

- There is no upper age limit for cochlear implantation in adults. 

- For elderly patients, the indication is determined after a psychocognitive evaluation. 

- In general, there is no indication for primary implantation in adults with prelingual deafness.

D- Contraindications:

• Pathologies of the external or middle ear: (otitis externa ; seromucous otitis , tympanic perforation .... ) these must be treated before implant placement.
• Cochlear anomalies: total or partial agenesis (Mondini), absence of the Modiulus, ossification of the basal turn of the cochlea (labyrinthitis ossificans).
• Cochlear nerve agenesis.
• Patient with profound prelingual deafness reaching advanced age.

II - CT scan of the petrous bones :

• Essential for all pre-implant assessments
• Technique: Helicoidal acquisition on the petrous bone without injection of iodinated PDC.

A - Elements to Include in the Report:

A-1: Search for Anomalies:

               - External Ear:

                               - Obstruction (e.g., otitis). 

                              - Atresia of the external auditory canal (EAC). 

                - Middle Ear: 

                                 - Aeration of the tympanic cavity. 

                                - Evaluation of the walls of the tympanic cavity (e.g., tegmen tympani, scutum). 

                                - Abnormalities of the ossicular chain (e.g., hypoplasia, erosion, lysis).

               - Inner Ear: 

                               - Search for otospongiotic lesions. 

                               - Cochleovestibular anomalies.

A-2: Eliminate contraindications:

Study of the outer and middle ear: otitis (Figure 3) must be treated before the implant is placed.

Evaluation of the mastoid air cells and the presence of chronic otitis media or cholesteatoma that could complicate surgery.

Study of the cochlea:

• Coiled cochlea (2 and a half turns): Partial or total agenesis, dysplasia, cochleovestibular cavity (Figure 2).
• Visualization of the Modiulus: Absence of the Modiulus is a contraindication.
• Ossification of the basal turn of the cochlea (labyrinthitis ossificans) (Figure 4).

The importance of assessing the integrity of the ossicular chain and any prior surgical alterations (Figure 5).

Cochlear nerve anomalies (Compare with rock MRI data):

• Measurement of the cochlear nerve canal (Figure 6):
• Normal: (1.5-2mm)
• If < 1.5 mm (cochlear nerve hypoplasia or absence)
• Measurement of the width of the CAI:
• Normal: ( > 2.5 mm )
• If<2.5 mm: stenosis of the IAC (doubt about hypoplasia or absence of the cochlear nerve )

A-3 : Planning the therapeutic procedure :

 Dimensions of the cochlea

• Distance A (Figure 8 ) : From the round window to the lateral wall of the cochlea
• Formula according to Jolly:
• Cochlear canal dimensions =3.65A-3.63
• This determines the number and size of electrodes.

Round window (Figure 9):

• Height measurement:
• Normal: (1.5- 2 mm)
• If<1.5 mm: Narrow round window (surgical difficulty before introducing the electrodes)
• The surgeon will choose the ear with the highest window.

III - Standardized report.

• Study of the external, middle, and inner earElimination of contraindications:
• Cochlea: Present / Absent
• Dimensions of the internal auditory canal (IAC) and the cochlear nerve
• Factors compromising the success of implantation:
• Anomalies of the semicircular canals (measurement of the central bony island)
• Dilation of the vestibular aqueduct
• Cochlear ossifications
• Useful elements for the therapeutic procedure:
• Cochlear dimensions (Distance A)
• Height of the round window