The suprameatal approach: an alternative surgical technique for cochlear implantation

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The suprameatal approach: an alternative surgical technique for cochlear implantation

JONA KRONENBERG, LELA MIGIROV, Department of Otolaryngology and Head and Neck Surgery, Sheba Medical Center, Tel Hashomer and Sackler Faculty of Medicine, Tel-Aviv, Israel

ABSTRACT The suprameatal approach (SMA) for cochlear implantation was devel-oped in our department in 1999. This technique is based on retroauricular tympanotomy and does not include mastoidectomy. The SMA eliminates possible injury to the facial nerve and chorda tympani, shortens operative time, enables easier drilling of cochleostomy and better control of the electrode insertion, permits the preservation of residual hearing and improves the aesthetic results. Copyright © 2006 John Wiley & Sons, Ltd.

Keywords: cochlear implant; surgery; technique

The suprameatal approach (SMA) (Kronenberg et al., 2001, 2002, 2004) was developed in our department as an alternative to the classic mastoidectomy- posterior tympanotomy approach (MPTA) (Chouard and MacLeod, 1976). The trigger for the development of this technique was the desire to simplify the surgical procedure and to avoid damage to the facial nerve and chorda tympani. Recently, non-mastoidectomy approaches have been used successfully for cochlear implant (CI) surgery in different centres (Kronenberg et al., 2001, 2002, 2004; Häusler, 2002; Kiratzidis et al., 2002; Arnoldner et al., 2005; Djalilian et al., 2005).

More than 300 patients underwent CI with the SMA in our department between September 1999 and July 2005. The current paper elucidates the SMA and describes the advantages of using this technique in CI surgery.

Surgical technique

The patient is placed in the supine position as for retroauricular tympanotomy. A skin flap is raised following a small inverted J-shaped skin incision. A periosteal flap is elevated using a periosteal elevator with the creation of a posterior pouch, bony well and two to four holes for cochlear implant body fixation. The skin of the posterior wall of the external auditory canal is incised horizontally 5 mm lateral

Cochlear Implants InternationalCochlear Implants Int. 7(3), 142–147, 2006Published online in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/cii.307

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Cochlear Implants Int.7(3),142–147,2006Copyright©2006JohnWiley&Sons,Ltd DOI:10.1002/cii

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The suprameatal approach: an alternative surgical technique for cochlear implantation 143

to the annulus and is retracted anteriorly with a 1/4 inch Penrose drain (Figure 1). A six o’clock vertical incision is made in the meatal skin and a tympano-meatal flap is elevated to expose the middle ear cavity. The chorda tympani is exposed and a 1 mm to 2 mm long groove is then drilled into the outer attic wall postero-superior to the chorda tympani and lateral to the body of the incus. The visualiza-tion of the incus body serves as a target for drilling and prevents injury to the facial nerve, which is located medial to the incus. A cochleostomy is performed in two stages. Initially, drilling is performed in the promontory using a 0.8 mm diamond burr, antero-inferior to the oval window until the membrane of the spiral ligament is exposed but not penetrated. This avoids entry of blood and debris into the cochlea during the subsequent bony work. A tunnel is drilled in the one o’clock position of the suprameatal region, posterosuperior to the external auditory meatus in an oblique line from postero-superior to antero-inferior ending in the groove. In cases when a low-lying dura has been identified on preoperative computed tomography (CT), the middle cranial foss dura is first exposed using a 2 mm cutting burr in order to avoid possible injury by drilling. Once the dura has been visualized, a 1.5 mm cutting burr followed by a 1.5–2 mm diamond burr are used for creation of the tunnel, depending on the distance between the middle fossa dura and the wall of the external auditory canal. Care is taken to maintain a safe distance between the tunnel and the bony external auditory canal wall, which may vary between 3 mm and 7 mm. The tunnel is created inferior to the dura, with a mean length of 12 mm in adults and 7 mm in children and a diameter varying between 2 mm and 2.5 mm. The spiral ligament is incised and the cochleostomy is widened in the direction of the round window in order to ensure entry into the scala tympani. The electrodes are passed through the suprameatal tunnel and groove into the cochleostomy (Figures 2 and 3). Small pieces of connective tissue are used

Figure 1: Anterior displacement of the tympano-meatal flap.


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for meticulous sealing of the cochleostomy and one piece is placed between the chorda and tympanic membrane. The implant is placed into the posterior pouch and the ball electrode is positioned underneath the temporalis muscle. The tym-panomeatal flap is placed back and fixed by small pieces of gel-foam. The subperi-osteal flap is used to cover the electrode.

Figure 2: A schematic drawing of the SMA surgical technique. The electrodes are inserted into the lateral opening of the suprameatal tunnel and through the groove medial to the chorda tympani into the cochleostomy.

Figure 3: Intraoperative photograph of the electrode insertion. The electrodes are seen exiting the medial end of the suprameatal tunnel, passing through the groove medial to the chorda tympani and into the cochleostomy.


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Discussion

Our cochlear implant programme commenced in 1989. Ten years and 132 cochlear implants later we searched for ways in which the surgical procedure could be sim-plified. The conventional MPTA provides access to the middle ear through the facial recess, which is a space between the chorda tympani and the mastoid vertical segment of the facial nerve. It may occasionally be a narrow ‘keyhole’, especially when the facial nerve is located anteriorly or when the recess is not yet developed, as in young children up to 2 years of age. Working through a narrow ‘keyhole’ may lead to difficulties in identifying the landmarks used for cochleostomy drilling, especially in cases of malformed and ossified cochlea. In the SMA technique, cochleostomy and electrode insertion are performed through the external auditory canal following elevation of a tympanomeatal flap, which provides a wide exposure of the middle ear and promontory.

In the MPTA, the facial nerve and chorda tympani are used as landmarks in demarcating the facial recess as a route of penetration into the middle ear. Proxim-ity of drilling through a narrow recess may lead to injury of the facial nerve or chorda tympani. In cases of a narrow facial recess, sacrifice of the chorda tympani is needed but the significance of this has not yet been elucidated. Damage to the chorda tympani nerve was described in 5.2% to 20% of cases (Hoffman and Cohen, 1995; Johnson et al., 1997; Lenarz et al., 1999; Proops et al., 1999; Bhattia et al., 2004; Green et al., 2004) and the possibility of facial nerve injury, both temporary (0.3% to 3%) and permanent (0.6%), has been reported (Cohen and Hoffman, 1991; Hoffman and Cohen, 1995; Johnson et al., 1997; Balkany et al., 1999; Kempf et al., 1999; Lenarz et al., 1999; Hehar et al., 2002; Fayad et al., 2003; Bhattia et al., 2004; Green et al., 2004).

In the SMA, the facial nerve is not in the path of drilling and the tunnel that is created for electrode insertion is at a safe distance from the course of the facial nerve, both in its tympanic and mastoideal segments. In addition, the facial nerve is well protected by the body of the incus. The chorda tympani nerve is exposed and preserved using the same approach as in stapes surgery and there is no need to sacrifice the nerve. The drilling of the suprameatal tunnel begins with exposure of the middle fossa dura to avoid possible injury. No cases of facial nerve or chorda tympani injury were seen in any of the patients operated with the SMA.

The posterior tympanotomy technique is a familiar approach combining mas-toidectomy and tympanoplasty in cholesteatoma surgery. However, in many insti-tutions this technique has been substituted by canal-wall down procedures and attico-antrotomy. As a result, in these institutions, posterior tympanotomy tech-nique is less widely practised. The suprameatal approach is based on the retro-auricular tympanotomy approach familiar to all otological surgeons.

The exclusion of mastoidectomy in the SMA implies less drill work. Therefore, the duration of surgery is shortened and the aesthetic results are improved with no retroauricular bony defects. Decreased bony drilling may be beneficial for CI under local anaesthesia and intraoperative ability to test hearing.


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In summary, using a non-mastoidectomy approach such as SMA in CI surgery provides a wide exposure of the middle ear with better visualization of the promon-tory and enables easier drilling of the cochleostomy and better control of the insertion of the electrode in cases of malformed and ossified cochlea. Better visibil-ity of the cochleostomy site permits the preservation of residual hearing and ensures insertion of the electrode into the scala tympani. The exclusion of mastoidectomy in the SMA shortens the duration of surgery to about 1 hour, improves the aes-thetic results with no retroauricular bony defects and eliminates possible injury to the facial nerve and chorda tympani. Short operative time and minimal drilling are conditional for implantation under local anesthesia. Damage to chorda tympani had become a very important issue because the number of bilaterally implanted patients has increased.

References

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Kronenberg J, Baumgartner W, Migirov L, Dagan T, Hildesheimer M (2004) The suprameatal approach: an alternative surgical approach to cochlear implantation. Otology and Neurotology 25: 41–45.

Kronenberg J, Migirov L, Baumgartner WD (2002) The suprameatal approach in cochlear implant surgery: our experience with 80 patients. ORL Journal for Oto-Rhino-Laryngology and its Related Specialties 64: 403–405.

Kronenberg J, Migirov L, Dagan T (2001) Suprameatal approach: new surgical approach for cochlear implantation. Journal of Laryngology and Otology 115: 283–285.

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Address correspondence to: Lela Migirov, Department of Otolaryngology and Head and Neck Surgery, Sheba Medical Center, Tel Hashomer, 5262l Israel. Tel.: (+972) 3-5302242. Fax: (972) 35305387. Email: [email protected]

The suprameatal approach: an alternative surgical technique for cochlear implantation

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