The utilization of round window membrane surface tension in facilitating slim electrodes insertion during cochlear implantation

Prof. Dr. IHAB M. NADA Associate Professor Otorhinolaryngology and Head & Neck surgery Misr University for Science & Technology Consultant Otology Surgeon Authors:

- Ihab Nada Department of Otorhinolaryngology, Faculty of Medicine, Misr University for Science and Technology, 6th of October City, Egypt

- Ahmed Nabil Abdelhamid Department of Otorhinolaryngology, Faculty of Medicine, Ain Shams University, 6th Nile Valley Street, Hadayek Alkoba, Cairo 11331, Egypt

- Ahmed Negm Department of Otorhinolaryngology, Faculty of Medicine, Misr University for Science and Technology, 6th of October City, Egypt Disclosure:

Nothing to be disclosed. • Abu Al Qasim al Zahrawi (Albucasis) was born in madinet al Zahra near Cordoba in Islamic spain on 936 CE and died in 1013 CE. He descended from Ansar tribe of arabia who had settled in spain. • His Book Al-Tasrif was completed about 1000 CE and was the result of almost 50 years of medical practice, His 300 pages book influenced the progress of medicine and surgery in Europe after it was translated into latimn in the late 12th century. Advantages of round window route

• Reduced risk of intra cochlear trauma, as it requires no direct drilling into the cochlea • No bone dust into scala tympani • The array will necessarily be introduced into the scala tympani and utilise the entire basilar turn for electrical stimulation, enabling a more perimodiolar position adjacent to the osseous spiral lamina thus increasing the likelihood of stimulating residual dendrites Surgical procedure • Posterior tympanotomy : round window route was used • Opening of the round window by a fine pick antrosuperiorly near the round window anulus creating a small slit incision about 0.6 mm perserving the integrity of the round window to use its tensile strength as a stent, lever or support to the electrode during insertion • Emphasis on soft cochlear implantation was ensured Tensile strength of the round window

• Watanbe et al., 2016. Studied the rupture criteria of freshly harvested RWMs of guinea pigs in situ using Nano- identification. They concluded that the tensile stress of the RWM is 19.4 megapascal (Mpa) (1Mpa=1,000,000 pascals) Study idea & design

The aim of our study was to compare two operative techniques for slim electrode insertion with their impact on insertion time , ease , insertion trials , kinking and residual hearing .

1) Removing the round window membrane or cruciate incision ( Group B).

2) Slit incision of the round window membrane antero superiorly near the annulus ( Group A ) . with bony overhang (round window niche) removal in both cases ,Patients included were those with with type I and type IIa RWM exposure (according to St. Thomas hospital classification) St thomas classification

• Type I RWM describes the exposure of the RWM such that it is observed in its entirety. • Type II describes partial exposure and is sub-divided into Type IIa and IIb; in Type IIa, more than 50 % but less than 100 % of the RWM is exposed and in Type IIb, the exposure is less than 50 % but more than 0 %. • Type III, the RWM cannot be identified at all even after best surgical effort A prospective study was undertaken on (paediatric) patients undergoing cochlear implantation from september 2014 to September 2016 ( 240 cases ) at a cochlear implant centre in a tertiary referral hospital.

From these cases , 118 cases were included in this study with age: 18 months -5 years

Devices used were :

MEDEL flex 28 ( 82 CASES ) OTICON EVO ( 30 cases ) COCHLEAR FREEDOM ( 6 CASES )

70 cases had slit incision of the round window (Group A) 48 cases had RWM removal or cruciate incision (Group B) • From the study groups 40 patients were selected , 20 from group (A) & 20 from group (B) , whose age is from 3 years & 10 months – 5 years and had residual low frequency hearing evidenced by play audiometry to study the effects of both techniques on hearing preservation . Technique

• Round window membrane incision is made in anterior border, from superior to inferior to avoid penetration of the basilar membrane

• Slit incision of the RWM should be enough to allow some perilymph to go out (gentle perilymph leak is quite safe), to avoid sudden rise of intracochlear pressure during electrode insertion Large RWM opening Small opening in RWM Electrode insertion through small opening in RWM Video : Results • Group (A) :70 cases underwent slit incision (68 cases smooth insertion, 2 cases difficult insertion)

Group (B) : 48 cases RWM removal or cruciate incision (13 cases smooth insertion , 35 cases difficult insertion (kinking, floppiness, increase operative time, multiple insertion trials)

• Residual low frequency hearing preservation was observed in (16) patients from the twenty patients who were selected from group (A) • • Residual hearing preservation was observed in ( 8 ) patients from 20 patients who were selected from group (B) , while 12 have lost the low frequency residual hearing (changing from profound to total hearing loss) . Overall incidence of difficult insertion in the two study groups. Rate of preservation of low-frequency hearing in the two study groups. a Preoperative and b postoperative audiograms showing preserved low frequency hearing after slit incision of RWM during right side cochlear implantation. Red and blue colours are the audiograms of the right and the left sides, respectively a Preoperative and b postoperative audiograms showing total loss of low frequency hearing after cruciate incision of RWM during right side cochlear implantation. Red and blue colours are the audiograms of the right and the left sides, respectively Conclusion

• Tensile strength of the round window membrane after minimal penetration offers support to the slim electrodes during its introduction minimizing kinking and floppiness of the electrode, hence shortening the maneuver time and minimizing the number of trials and facilitating easy smooth electrode introduction so decreasing intra cochlear trauma & leading to more hearing preservation in slim electrodes . THANK YOU