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Present Surgical Approaches for
Cochlear Implantation (A Review)

*K. Assenova , †S. Stoyanov, *T. Karchev

*Medical University Sofia, ENT Department, Bulgaria
†Ministry of Interior – Medical Institute, ENT Department, Sofia, Bulgaria

ABSTRACT

Objective: The aim of this paper is to review presently used surgical approaches for cochlear implantation. The main steps of surgery are presented. The advantages and disadvantages of transmastoid, suprameatal and middle cranial fossa approaches are discussed. Some historical data are also reviewed.
Setting: Medical University Sofia, ENT Department, Ministry of Interior – Medical Institute, ENT Department
Study Design: A case review.
Methods: The transmastoid approach, the suprameatal approach, the middle cranial fossa approach
Keywords: Cochlear implantation, Transmastoid approach, Middle fossa approach, Electrode insertion.
Pro Otology 2-3:96—97, 2004

Introduction

Cochlear implantation is an operation for introduction of electrode into the cochlea for electrical stimulation of auditory nerve. Recently it became a commonly accepted method for rehabilitation of patients with severe sensorineural hearing loss. The aim of this paper is to review presently used surgical approaches for cochlear implantation.

The idea of cochlear implantation is based on the discovery of Wever and Bray in 1936 that conduction of acoustic information from the sensory organ of Corti to the hearing nerve is accompanied by the appearance of bio-electrical potentials - the so called microphone potentials. In 1957 Djourno and Eyres operate the first patient with bilateral cholesteatoma and place the active electrode directly over the auditory nerve. Pioneers in cochlear implantation are W. House and G. Clark. Contemporary multichannel cochlear implants have been widely implicated in surgical practice during the nineties of the past century. The surgical technique for placement of a cochlear implant has continuously developed and improved.

The transmastoid approach

So far, most often is used the transmastoid approach. The main steps, which have not significantly changed since its formulation by W. House in 1961, are: mastoidectomy, posterior tympanotomy, cochleostomy and insertion of the active electrode. The following anatomic landmarks should be visualized: long process of incus, incudostapedial joint, eminentia pyramidalis with stapedial muscle tendon, promontory and round window niche. Cochleostomy is performed anteriorly and superiorly to round window niche by a diamond burr. The diameter of the opening varies from 1.3 to 2 mm. The described technique is difficultly applied in patients with malformations of internal and middle ear or ossification changes in the cochlea, e.g. after meningitis. There is also a significant risk of facial nerve injury.

Modification of O’Donoghue and Nikolopoulos

O’Donoghue and Nikolopoulos propose a modification of the incision in posterior tympanotomy. They use a short oblique straight posauricular incision without shaving the patient’s hair. The bony well of the implant is drilled inside of small subperiosteal pocket. The modification is well accepted by the patients and parents and diminishes the risk of flap complications.

The suprameatal approach

Kronenberg J. (2001) introduces a new approach for cochlear implantation by means of which mastoidectomy is avoided and the duration of the operation is decreased. This is the so-called suprameatal approach. The electrode is introduced into the cochlea through a tunnel drilled in the suprameatal bone region superior to Henle`s spine. The average length of the drilled tunnel in children is 7 mm and in adults - 12 mm. Cochleostomy is performed anteriorly and inferiorly to the oval window. The advantages are: simplified and shorter surgical intervention; broad view on the promontory; significantly lower risk for the facial nerve and chorda tympani; better esthetic results.

Modification of Kiratzidis

Kiratzidis T. (2001) proposes the electrode to be placed in a suprameatal tunnel, which is formed by a specially constructed by the author perforator.

Kiratzidis and Kronenberg use previous tympanotomy for direct anatomical assessment and work in the middle ear. The facial recess is visualized from the ear canal that allows a limited mastoidectomy (extended antrotomy). Such technique is used in Bulgaria by prof. Zenev and prof. Kunev.

Many pathologic conditions like malformations of middle and internal ear, chronic otitis media and radical mastoidectomy are contraindications for the above mentioned approaches for cochlear implantation. There is a risk for infection and meningitis when the introduction of the electrode is performed through potentially contaminated with pathogenic microorganisms areas like the radical cavity and infected middle ear. Other possible complications include liquorrea, seroma, wound infection, edema, and development of secondary cholesteatoma.

The middle cranial fossa approach

For these reasons Colletti V. and al. (1998) propose the placement of cochlear implant to be performed through the middle cranial fossa. The anatomy of petrous bone makes the approach to the cochlea through middle cranial fossa possible. The cochlea is in contact with the anterior petrous wall in its antero-superior region. The basal and middle turns are reachable in the angle between the labyrinthine portion of facial nerve and n. petrosus superficialis major. The surgical technique is as follows: A temporal craniotomy measuring 3 x 3 cm is performed. The lower bony margin should lie maximally close to the floor of middle cranial fossa. The bone flap is removed plastically. The dura is elevated from the middle cranial fossa floor towards foramen spinosum. A. meningea media is visualized. N. petrosus superficialis major is identified and followed to ganglion geniculi. The elevation of dura continues medially till the location of eminentia arcuata. The bone is drilled in a triangular area limited by n. petrosus superficialis major and the projection of the labyrinthine portion of facial nerve. The basal turn of the cochlea is easily identified by its bluish color. A cochleostomy of about 1.5 mm is performed in its highest part. The authors reported better results for speech recognition compared to patients operated by transmastoid approach. The method makes possible the stimulation of middle and apical turn of the cochlea, where the number of functioning ganglion cells is usually greater, compared to the basal turn.

Conclusion

In conclusion, it can be recapitulated that so far most often is used the transmastoid approach. During the last decade appeared many reports for problems, related to this method. The optimal technique for introduction of the electrode into the cochlea continues to be an object of intensive research.

REFERENCES

  1. House W. Cochlear implant. Ann ORL 1976;85(Supll)27:2-6.

  2. Webb RL, Lenhard E, Clark GM, et al. Surgical complications with the cohlear multiple-channel implant: experience at Hanover and Melbourne. Ann ORL 1991;100:131-6.

  3. Colletti V, Fiorino FG, Carner M, Pacini L. Basal turn cochleostomy via the middle fossa route for cochlear implant insertion. Am J Otol 1998;19:778-84.

  4. Kiratzidis T. “Veria operation“:cochlear implantation without a mastoidectomy and a posterior tympanotomy. Adv ORL 2000;57:127-30.

  5. Kronenberg J, Migirov L, Dagan T. Suprameatal approach: new surgical approach for cochlear implantation. J Laryngol Otol.2001;115(4):283-5.

  6. O’Donoghue GM, Nikolopoulos TP. Minimal access surgery for pediatric cochlear implantation. Otol Neurotol. 2002; 23(4):891-4.

  7. Colletti V, Fiorino FG, Saccetto L, Giarbini N, Carner M. Improved auditory performance of cochlear implant patients using the middle fossa approach. Audiology 1999;38(4):225-34.

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