Blinded comparison of computed tomography, ultrasound and needle methods to measure skin flap thickness for cochlear implantation

Abstract

Purpose

Patient suitability for cochlear implant (CI) devices compatible with magnetic resonance imaging and CI processor configuration is dependent on their retro-auricular skin flap thickness. This is typically measured intra-operatively using a needle and therefore patients are not guaranteed their implant of choice prior to surgery. We aimed to identify an accurate method to measure skin flap thickness pre-operatively to streamline CI selection and simplify the consent process.

Methods

Blinded prospective skin flap thickness measurements for patients undergoing CI surgery were recorded using pre-operative computed tomography (CT) and ultrasound (US), and intraoperative needle measurement.

Results

Fifty-six adult patients (36 females, 20 males; mean age 59 years) were included. The mean flap thickness was measured highest by CT (6.9 mm, 95% CI 6.5–7.3 mm), followed by US (6.3 mm, 95% CI 5.9–6.7 mm) and lastly needle (5.5 mm, 95% CI 5.1–5.9 mm) (p < 0.0001). A strong positive correlation (p < 0.001) was noted between all three modalities: CT vs needle (r = 0.869), US vs needle (r = 0.865), and CT vs US (r = 0.849).

Conclusion

Accurate, non-invasive measurement of skin flap thickness prior to CI surgery can be achieved using CT or US. We recommend the routine use of US in the outpatient clinic to minimise unnecessary radiation exposure.

Keywords:

• Cochlear implant
• Surgery
• Skin flap thickness
• Ultrasound
• Computed tomography
• Needle

Acknowledgements

This research was supported by the National Institute for Health Research Manchester Biomedical Research Centre. We would like to thank our patients who kindly participated in this study.

Disclaimer statements

Contributors: None.

Funding: This research was supported by Cochlear.

Conflict of interests: No potential conflict of interest was reported by the author(s).

Ethics approval: None.

Additional information

Notes on contributors

Rohma Abrar

Dr. Rohma Abrar is an ENT Specialty Trainee at Doncaster and Bassetlaw Teaching Hospitals NHS Foundation Trust. Miss Emma Stapleton is Consultant Otolaryngologist, Cochlear Implant and Skull Base Surgeon at Manchester University NHS Foundation Trust.