A comparison of imaging techniques to measure skin flap thickness in cochlear implant patients to enable pre-operative device selection

Abstract

Objectives

Magnetic resonance imaging (MRI)-compatible cochlear implants have weaker internal magnets than non-MRI-compatible devices. Their suitability for individual patients is limited by skin flap thickness, traditionally measured with a needle in the operating theatre. We aimed to establish the accuracy of imaging modalities to measure skin flap thickness pre-operatively, with the goal of streamlining device selection and simplifying the consent process.

Methods

Skin flap measurements were taken using ultrasound (US), computed tomography (CT) and MRI and compared for agreement with intra-operative needle measurement.

Results

Twenty-seven skin flaps were included. Absolute agreement between needle and imaging methods was low: needle/US: 44.4% (95% confidence interval [CI]: 27.7–62.7), needle/CT: 39.1% (95% CI: 22.2–59.2), needle/MRI: 20.8% (95% CI: 9.2–40.5). However, US and CT showed 95.7% agreement (95% CI: 76.0–99.8) with intraclass correlation of 0.996 (95% CI: 0.991–0.998) and narrow Bland–Altman limits of agreement (−0.37, 0.45 mm). BMI and skin flap thickness showed a significant positive correlation (r_s= 0.664, P = 0.002) but no significant correlation was observed for age (P = 0.659).

Discussion

The high level of agreement between US and CT suggests that there are more accurate measurements of skin flap thickness compared with needle or MRI. Needle measurements are consistently smaller.

Conclusion

The use of CT or US should be considered when making pre-operative device choices.

Keywords:

• Cochlear Implantation
• Skin Flap Thickness
• Imaging
• Radiology
• Patient Choice
• Consent

Acknowledgements

The authors would like to acknowledge Ms. Azita Rajai for her invaluable support with statistical analysis. This work was submitted as Jacob Rees’ MCh thesis and was awarded a Distinction by the University of Edinburgh (2020). This work was presented at the BOARS National Research Conference March 2021 and awarded the Philip Stell Prize for best oral presentation. This research was supported by the NIHR Manchester Biomedical Research Centre.

Disclosure statement

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

Additional information

Notes on contributors

Jacob Rees

Jacob Rees qualified from the University of Manchester in 2016. This work formed the basis of his Masters dissertation for the University of Edinburgh. He was awarded a distinction. Rohma Abrar is an ENT trainee in the North of England. Emma Stapleton is a Consultant Otolaryngologist and Cochlear Implant Surgeon at the Richard Ramsden Center for Auditory Implants, Manchester Royal Infirmary.

Rohma Abrar

Rohma Abrar is an ST1 run-through trainee in ENT, based in Yorkshire and Humber.

Emma Stapleton

Emma Stapleton is a Consultant Otolaryngologist and Cochlear Implant Surgeon at the Manchester Royal Infirmary, and Clinical Lead for the Manchester Cochlear Implant Programme.