Adaptive cochleostomy is the concept that a single type of cochleostomy is not ideal in all cases. Rather, the type of cochleostomy used should be selected based on the anatomy of the patient and the physical characteristics of the electrode to be inserted. In short, the cochleostomy should be adapted to the patient’s anatomy and the electrode used. Cochleostomy is used here to mean an enduring opening into the cochlea through which an electrode is inserted.
Advocates of round window membrane (RWM), extended RWM and bony cochleostomy approaches have claimed that their preferred technique is best. Support for each is provided in the literature (1-4) RWM insertion may minimize drill trauma, prevent bone dust and blood from entering the scala and reduce leakage of perilymph; extended RWM cochleostomy may provide a more favorable insertion trajectory when the RWM is angled too inferiorly; and bony cochleostomy allows better electrode alignment with the axis of the scalar lumen, especially important when inserting larger, stiffer or pre-curved electrodes (1). However, the one-size-fits-all arguments do not take into account common variations in patient anatomy and electrode configuration.
We initially presented the concept of Adaptive Cochleostomy at CI2012 in Baltimore (5), proposing that no single method of cochleostomy was ideal in all cases. Shapira et al. (6) had already demonstrated a normal variation in angulation of the RWM of 27 – 65°. RWM insertion in the case of angulation >45° (13% of patients) can result in modiolar trauma, insertion into the vestibule and electrode transposition into S. vestibuli. In such cases, bony cochleostomy is preferred.
Recently Sun and colleagues3 from Hualien and Taichung, Taiwan and Hassepass and colleagues (7) from Freiburg compared hearing preservation following implantation via RWM vs. bony cochleostomies.
Sun et al. prospectively studied 20 recipients of a straight, flexible electrode inserted via RWM cochleostomy with 20 age- and sex-matched controls implanted through bony cochleostomy. There was no difference in low frequency hearing preservation between the two groups.
The Freiburg group used a different straight, flexible electrode and selected the cochleostomy site based on this concept of Adaptive Cochleostomy. In their retrospective study of 41 subjects, there were no substantial differences in insertion depth/angle or low frequency hearing preservation between the two groups.
A previous blog addressed the work of Wanna et al. (4) at Vanderbilt who demonstrated equally good results using an extended RWM approach.
Radiographic prediction of RW niche visibility was studied by Kashio and colleagues (8) at the University of Tokyo using standard HRCT with 1 mm slice thickness. The authors were able to categorize RW niche imaging findings into 1. invisible or nearly invisible; 2. partially visible; and 3. fully visible. It is yet to be seen if RWN visibility is related to RWM angulation.
Thin, straight, flexible electrodes are ideal for RWM insertion but should be considered for extended RWM or bony cochleostomy insertion when angulation of the RWM is greater than 45° (the RWM diameter appears to the surgeon to be less than that of a 1 mm diamond burr held in the same field of view). Thicker, stiffer or pre-curved electrodes may be best inserted by bony cochleostomy to take advantage of coaxial scalar placement.
1. Addams-Williams J, Munaweera L, Coleman B, Shepherd R, Backhouse S. Cochlear implant electrode insertion: in defence of cochleostomy and factors against the round window membrane approach. Cochlear Implants Int. 2011;12 Suppl 2:S36-9.
2. Adunka et al. Cochleostomy Versus Round Window Insertions…. Otology & Neurotology 2014; 35: 613–618
3. Sun CH, Hsu CJ, Chen PR, Wu HP. Residual hearing preservation after cochlear implantation via round window or cochleostomy approach. Laryngoscope 2015; doi: 10.1002/lary.25122. (Epub ahead of print).
4. Wanna GB, Noble JH, Carlson ML, et al. Impact of electrode design and surgical approach on scalar location and cochlear implant outcomes. Laryngoscope 2014. 124: Sup 6; S1-S7.
5. Balkany TJ. Adaptive Cochleostomy. CI2012, Twelfth International Congress on Cochlear Implants and Other Implantable Auditory Technologies. Baltimore, May 2 – 12, 2012.
6. Shapira Y, Eshraghi A, Balkany TJ. The perceived angle of the round window affects electrode insertion trauma in round window insertion – an anatomical study. Acta Oto-Laryngologica 2011;131:284-289.
7. Hassepass F, Aschendorff A, Bulla S, Arndt S, Maier W, Laszig R, Beck R. Otol Neurotol. 2015;36(6):993-1000.
8. Kashio, Akinori; Sakamoto, Takashi; Karino, Shotaro; Kakigi, Akinobu; Iwasaki, Shinichi; Yamasoba, Tatsuya. Predicting Round Window Niche Visibility via the Facial Recess Using High-Resolution Computed Tomography. Otology & Neurotology: 2015 - Volume 36 - Issue 1.